Single-ion-conducting block copolymers are of considerable interest as electrolytes for battery systems, as they eliminate overpotentials due to concentration gradients. In this study, we characterize a library of poly(ethylene oxide) (PEO)-based diblock copolymers where the second block is poly(styrene-4-sulfonyltrifluoromethylsulfonyl)imide with either cation: univalent lithium or divalent magnesium counterions (PEO–PSLiTFSI or PEO–P[(STFSI)2Mg]). The PEO chain length is held fixed in this study. Polymers were synthesized in matched pairs that were identical in all aspects except for the identity of the counterion. Using rheology, SAXS, DSC, and AC impedance spectroscopy, we show that the dependence of morphology, modulus, and conductivity on composition in these charged copolymer systems is fundamentally different from uncharged block copolymers. At a given frequency and temperature, the shear moduli of the magnesiated copolymer systems were approximately 3–4 orders of magnitude higher than those of the matched lithiated pair. The shear moduli of all of the lithiated copolymers showed liquid-like rheological features while the magnesiated copolymers did not. All of the lithiated copolymers were completely disordered (homogeneous), consistent with the observed rheological properties. As expected, the moduli of the lithiated copolymers increased with increasing volume fraction of the ion-containing block (ϕPSTFSI), and the conductivity decreased with ϕPSTFSI. However, the magnesiated copolymers followed a distinct trend. We show that this was due to the presence of microphase separation in the regime 0.21 ≤ ϕPSTFSI ≤ 0.36, and the tendency for microphase separation became weaker with increasing ϕPSTFSI. The magnesiated copolymer with ϕPSTFSI = 0.38 was homogeneous. The morphological, rheological, and conductivity properties of these systems are governed by the affinity of the cations for PEO chains; homogeneous systems are obtained when the cations migrate from the ion-containing block to PEO.

The development of solid polymer electrolytes for lithium battery applications is a challenge of profound technological significance. We have established a collaboration with the aim of understanding and designing improved polymer electrolytes that combines theoretical modeling, polymer synthesis, and experimental characterization. By studying diverse polymer chemistries, we have discovered that ion-solvation-site connectivity is an important feature of polymer electrolytes that is necessary for high lithium-ion conductance. We are employing this insight into search for improved polymer electrolytes, with promising early-stage results.

We report on the synthesis and characterization of a series of microphase-separated, single-ion-conducting block copolymer electrolytes. Salty nanoparticles comprising silsesquioxane cores with covalently bound polystyrenesulfonyllithium (trifluoromethylsulfonyl)imide (PSLiTFSI) chains were synthesized by nitroxide-mediated polymerization. Hybrid electrolytes were obtained by mixing the salty nanoparticles into a microphase-separated polystyrene-b-poly(ethylene oxide) (SEO) block copolymer. Miscibility of PSLiTFSI and poly(ethylene oxide) (PEO) results in localization of the nanoparticles in the PEO-rich microphase. The morphology of hybrid electrolytes was determined by scanning transmission electron microscopy. We explore the relationship between the morphology and ionic conductivity of the hybrid. The transference number of the electrolyte with the highest ionic conductivity was measured by dc polarization to confirm the single-ion-conducting character of the electrolyte. Discharge curves obtained from lithium metal–hybrid electrolyte–FePO4 batteries are compared to the data obtained from the batteries with a conventional block copolymer electrolyte.

Crystallization within block copolymers is a subject of considerable interest; however, little is understood about how the presence of an ion-containing block, such as poly[(styrene-4-sulfonyltrifluoromethylsulfonyl)imide (P[(STFSI)]), influences the crystallization behavior of single-ion conducting block copolymers derived from poly(ethylene oxide)-b-poly[(styrene-4-sulfonyltrifluoromethylsulfonyl)imide (PEO–P[(STFSI)]). In this study, we report on the crystallization behavior of PEO in a matched-set library of lithiated (PEO–P[(STFSI)Li]) and magnesiated (PEO–P[(STFSI)2Mg]) single-ion conducting block copolymers that are disordered in the melt. Structural and thermal analysis of semicrystalline samples prepared by quenching amorphous melts reveals that total PEO crystallinity is independent of cation identity. Furthermore, crystallization induces the formation of lamellar nanostructures regardless of the counterion present. However, the quality of the PEO crystallites and concomitant nanostructures appears to be strongly influenced by counterion identity; magnesiated samples demonstrate more disorder at both the crystalline and nanostructural level. By monitoring PEO crystallization with in situ small and wide-angle X-ray scattering, we show that PEO crystallizes from a homogeneous melt within PEO–P[(STFSI)Li] but is hindered by the presence of disordered concentration fluctuations within the magnesiated samples. Thus, counterion identity influences PEO crystallization by controlling the miscibility of the polymer blocks within the crystallizing melt.

Motivated by the need for developing membranes for biofuel purification, we made pervaporation membranes by casting a polystyrene-b-polydimethylsiloxane-b-polystyrene (SDS) triblock copolymer using toluene, cyclohexane, and hexane as casting solvents. The three solvents have different affinities for each of the blocks of the SDS, which enables the creation of membranes with different nano-morphologies using the same block copolymer. These membranes were used in pervaporation experiments with butanol/water mixtures as the feed solution. We quantify the effect of morphology on butanol and water permeabilities. Poorly-ordered granular morphology, obtained from hexane-cast membranes, is optimal for selective butanol transport. Butanol permeability was a more sensitive function of morphology than water permeability. Butanol uptake measurements showed that morphology had negligible effects on solubility. Therefore, we attribute the dependence of permeability on morphology to differences in diffusivities.

•We synthesized solid fluorinated electrolytes using PFPE with methacrylate groups.•Crosslinking was done using thermally and UV activated curing reactions.•POSS nanoparticles were used for the thermally crosslinked electrolytes.•LiTFSI solubility limit in solids is higher than that of liquid electrolytes.•VTF framework is used to quantify the factors affecting the ionic conductivity.Perfluoropolyethers (PFPE) are commercially available non-flammable short chain polymeric liquids. End-functionalized PFPE chains solvate lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt and these mixtures can be used as electrolytes for lithium (Li) batteries. Here we synthesize and characterize a new class of solid PFPE electrolytes. The electrolytes are made by either thermal or UV crosslinking PFPE chains with urethane methacrylate end-groups. For the synthesis of thermally crosslinked electrolytes, polyhedral oligomeric silsesquioxane (POSS) with organic acrylopropyl groups was used as crosslinker agent, while for UV cured electrolytes a photoinitiatior was used. We present thermal, morphological, and electrical data of the solid electrolytes. We compare these properties with those of the two parent liquids (PFPE with urethane methacrylate end-groups and POSS with acrylopropyl groups) mixed with LiTFSI. The solubility limit of LiTFSI in the PFPE-based solids is higher than that in the liquids. The conductivity data are analyzed using the Vogel–Tamman–Fulcher equation. The concentration of effective charge carriers is a strong function of the nature of the solvent (solid versus liquid) whereas the activation energy is neither a strong function of the nature of the solvent nor salt concentration.

Incipient microphase separation is observed by wide angle X-ray scattering (WAXS) in short chain multiblock copolymers consisting of perfluoropolyether (PFPE) and poly(ethylene oxide) (PEO) segments. Two PFPE–PEO block copolymers were studied; one with dihydroxyl end groups and one with dimethyl carbonate end groups. Despite having a low degree of polymerization (N ∼ 10), these materials exhibited significant scattering intensity, due to disordered concentration fluctuations between their PFPE-rich and PEO-rich domains. The disordered scattering intensity was fit to a model based on a multicomponent random phase approximation to determine the value of the interaction parameter, χ, and the radius of gyration, Rg. Over the temperature range 30–90 °C, the values of χ were determined to be very large (∼2–2.5), indicating a high degree of immiscibility between the PFPE and PEO blocks. In PFPE–PEO, due to the large electron density contrast between the fluorinated and non-fluorinated block and the high value of χ, disordered scattering was detected at intermediate scattering angles, (q ∼ 2 nm−1) for relatively small polymer chains. Our ability to detect concentration fluctuations was enabled by both a relatively large value of χ and significant scattering contrast.

Perfluoropolyethers (PFPEs) are polymer electrolytes with fluorinated carbon backbones that have high flash points and have been shown to exhibit moderate conductivities and high cation transference numbers when mixed with lithium salts. Ion transport in four PFPE electrolytes with different endgroups was characterized by differential scanning calorimetry (DSC), ac impedance, and pulsed-field gradient NMR (PFG-NMR) as a function of salt concentration and temperature. In spite of the chemical similarity of the electrolytes, salt diffusion coefficients measured by PFG-NMR and the glass transition temperature measured by DSC appear to be uncorrelated to ionic conductivity measured by ac impedance. We calculate a non-dimensional parameter, β, that depends on the salt diffusion coefficients and ionic conductivity. We also use the Vogel–Tammann–Fulcher relationship to fit the temperature dependence of conductivity. We present a linear relationship between the prefactor in the VTF fit and β; both parameters vary by four orders of magnitude in our experimental window. Our analysis suggests that transport in electrolytes with low dielectric constants (low β) is dictated by ion hopping between clusters.

•We studied the effect of pore penetration in supported membranes.•Nanophase-separated block copolymer was chosen as the selective layer.•We measured butanol and water permeabilities of the membranes.•Pore penetration thickness was estimated from the permeability data.•Pore penetration was directly imaged via HAADF-STEM.It has long been recognized that the performance of supported membranes comprising a thin, selective layer and a microporous support layer, is affected by penetration of the selective layer into the porous support. We have attempted to shed light on this phenomenon using a combination of pervaporation experiments and hard angle dark-field scanning transmission electron microscopy (HAADF-STEM). We use a nanophase-separated polystyrene-b-polydimethylsiloxane-b-polystyrene (SDS) as the selective layer and microporous polytetrafluoroethylene (PTFE) as the support layer. Effective permeabilities of butanol and water were measured as a function of selective layer thickness using a dilute butanol/water mixture as the feed in pervaporation. We were able to estimate the pore penetration layer thickness by comparing experiments with model calculations. We were also able to directly observe the pore penetration by HAADF-STEM. The choice in using a nanophase-separated block copolymer as the selective layer enabled identification of the regions of pore penetration. The pore penetration layer thickness obtained from the HAADF-STEM micrographs corresponded well with estimates based on pervaporation.

Furfural produced from the biomass-derived xylose may serve as a platform molecule for sustainable fuel production. The Brønsted acid-catalyzed dehydration of xylose to furfural is plagued by side reactions that form a set of soluble and insoluble degradation products, collectively known as humins, which reduce the yield of furfural. The formation of humins can be minimized by removal of furfural, either by steam stripping or by liquid–liquid extraction (LLE). However, both these techniques are very costly. The goal of this study was to demonstrate the feasibility of using pervaporation, a membrane process, to remove furfural as it is produced. A laboratory-scale reactor/membrane system was designed, built, and tested for this purpose and its performance for furfural production was compared with that achieved by carrying out the reaction with and without furfural extraction by LLE. Furfural production assisted by pervaporation (with a commercially available membrane or a triblock copolymer membrane) or LLE produced comparable amounts of furfural, and more than could be achieved by reaction without extraction. A model of the reaction kinetics and the rate of furfural extraction was fit to the pervaporation- and LLE-assisted furfural production data and was used to predict the performances of these processes at near-complete xylose conversion. Pervaporation is shown to have two advantages over LLE: pervaporation extracts a greater fraction of the furfural produced and the furfural concentration in the permeate phase is significantly higher than that present in the extractant phase obtained by LLE. It is noted that further improvement in the separation of furfural from the aqueous phase where it is produced can be achieved by using a more-permeable, thinner pervaporation membrane of larger area, and by operating the membrane at the reaction temperature.

•We report on the morphology and thermal properties of porous separators.•Polyolefins and polytetrafluoroethylene separators were characterized.•Carbonate- and perfluoropolyether-based electrolytes were investigated.•Conductivity of electrolyte-separators composite is reported.•Conductivity follows a master equation that depends on the electrolyte uptake only.In lithium batteries, a porous separator filled with an electrolyte is placed in between the electrodes. Properties of the separator such as porosity and wettability strongly influence the conductivity of the electrolyte-separator composite. This study focuses on three commercial separators: a single layer polypropylene (Celgard 2500), a trilayer polypropylene-polyethylene-polypropylene (PP-PE-PP), and a porous polytetrafluoroethylene (PTFE). Electron microscopy was used to characterize the pore structure, and these experiments reveal large differences in pore morphology. The separators were soaked in both carbonate- and perfluoropolyether-based electrolytes. The conductivity of the neat electrolytes (σ0) varied from 6.46 × 10−6 to 1.76 × 10−2 S cm−1. The porosity and wettability of the separator affect the electrolyte uptake that in turn affect the conductivity of electrolyte-separator composites. The conductivity of the electrolyte-separator composites (σ) was found to follow a master equation, σ = 0.51·σ0·ϕc3.2±0.2, where ϕc is the volume fraction of the electrolyte in each separator.

We introduce the use of block copolymer membranes for an emerging application, “drug capture”. The polymer is incorporated in a new class of biomedical devices, referred to as ChemoFilter, which is an image-guided temporarily deployable endovascular device designed to increase the efficacy of chemotherapy-based cancer treatment. We show that block copolymer membranes consisting of functional sulfonated polystyrene end blocks and a structural polyethylene middle block (S-SES) are capable of capturing doxorubicin, a chemotherapy drug. We focus on the relationship between morphology of the membrane in the ChemoFilter device and efficacy of doxorubicin capture measured in vitro. Using small-angle X-ray scattering and cryogenic scanning transmission electron microscopy, we discovered that rapid doxorubicin capture is associated with the presence of water-rich channels in the lamellar-forming S-SES membranes in aqueous environment.

We explore the relationship between the morphology and ionic conductivity of block copolymer electrolytes over a wide range of salt concentrations for the system polystyrene-block-poly(ethylene oxide) (PS-b-PEO, SEO) mixed with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI). Two SEO polymers were studied, SEO(16–16) and SEO(4.9–5.5), over the salt concentration range r = 0.03–0.55. The numbers x and y in SEO(x–y) are the molecular weights of the blocks in kg mol–1, and the r value is the molar ratio of salt to ethylene oxide moieties. Small-angle X-ray scattering was used to characterize morphology and grain size at 120 °C, differential scanning calorimetry was used to study the crystallinity and the glass transition temperature of the PEO-rich microphase, and ac impedance spectroscopy was used to measure ionic conductivity as a function of temperature. The most surprising observation of our study is that ionic conductivity in the concentration regime 0.11 ≤ r ≤ 0.21 increases in SEO electrolytes but decreases in PEO electrolytes. The maximum in ionic conductivity with salt concentration occurs at about twice the salt concentration in SEO (r = 0.21) as in PEO (r = 0.11). We propose that these observations are due to the effect of salt concentration on the grain structure in SEO electrolytes.

Single-ion conducting block copolymers, such as poly(ethylene oxide)-b-poly[(styrene-4-sulfonyltrifluoromethylsulfonyl)imide lithium] (PEO–P[(STFSI)Li]), represent an exciting new class of materials capable of improving the performance of solid-state batteries with metal anodes. In this work, we report on the synthesis and characterization of a matched set of lithiated (PEO–P[(STFSI)Li]) and magnesiated (PEO–P[(STFSI)2Mg]) single-ion conducting diblock copolymers. We measure the temperature dependence of ionic conductivity, and through analysis using the Vogel–Tamman–Fulcher (VTF) relation, demonstrate that ion dissociation is significantly lower for all PEO–P[(STFSI)2Mg] samples when compared to their PEO–P[(STFSI)Li] counterparts. The VTF parameter characterizing the activation barrier to ion hopping was similar for both cations, but the VTF prefactor that reflects effective charge carrier concentration was higher in the lithiated samples by an order of magnitude. We study the melt morphology of the single-ion conducting block copolymers using temperature-dependent X-ray scattering and use the mean-field theory of Leibler to extract the effective Flory–Huggins interaction parameter (χ) for PEO/P[(STFSI)Li] and PEO/P[(STFSI)2Mg] from the X-ray scattering data. We demonstrate a linear relationship between the charge-concentration-related VTF parameter and the parameter quantifying the enthalpic contribution to χ. It is evident that ion dissociation and block copolymer thermodynamics are intimately coupled; ion dissociation in these systems suppresses microphase separation.

•Electrolytes prepared using a systematic set of aliphatic polyesters and PEO/LiTFSI•Conductivity and glass transition are reported at varying salt concentration.•A new measure of salt concentration provides insight on polymer-salt interactions.•VTF fits are used to factor out the effect of segmental motion on conductivity.•Reduced conductivity elucidates the effect of changing monomer structure.Polymer electrolytes may enable the next generation of lithium ion batteries with improved energy density and safety. Predicting the performance of new ion-conducting polymers is difficult because ion transport depends on a variety of interconnected factors which are affected by monomer structure: interactions between the polymer chains and the salt, extent of dissociation of the salt, and dynamics in the vicinity of ions. In an attempt to unravel these factors, we have conducted a systematic study of the dependence of monomer structure on ionic conductivity, σ, and glass transition temperature, Tg, using electrolytes composed of aliphatic polyesters and lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt. The properties of these electrolytes were compared to those of poly(ethylene oxide) (PEO), a standard polymer electrolyte for lithium batteries. We define a new measure of salt concentration, ρ, the number of lithium ions per unit length of the monomer backbone. This measure enables collapse of the dependence of both the σ and Tg on salt concentration for all polymers (polyesters and PEO). Analysis based on the Vogel–Tammann–Fulcher (VTF) equation reveals the effect of different oxygen atoms on ion transport. The VTF fits were used to factor out the effect of segmental motion in order to clarify the relationship between molecular structure and ionic conductivity. While the conductivity of the newly-developed polyesters was lower than that of PEO, our study provides new insight into the relationship between ion transport and monomer structure in polymer electrolytes.

Polymers that conduct protons in the hydrated state are of crucial importance in a wide variety of clean energy applications such as hydrogen fuel cells and artificial photosynthesis. Phosphonated and sulfonated polymers are known to conduct protons at low water content. In this paper, we report on the synthesis phosphonated peptoid diblock copolymers, poly-N-(2-ethyl)hexylglycine-block-poly-N-phosphonomethylglycine (pNeh-b-pNpm), with volume fractions of pNpm (ϕNpm) values ranging from 0.13 to 0.44 and dispersity (Đ) ≤ 1.0003. The morphologies of the dry block copolypeptoids were determined by transmission electron microscopy and in both the dry and hydrated states by synchrotron small-angle X-ray scattering. Dry samples with ϕNpm > 0.13 exhibited a lamellar morphology. Upon hydration, the lowest molecular weight sample transitioned to a hexagonally packed cylinder morphology, while the others maintained their dry morphologies. Water uptake of all of the ordered samples was 8.1 ± 1.1 water molecules per phosphonate group. In spite of this, the proton conductivity of the ordered pNeh-b-pNpm copolymers ranged from 0.002 to 0.008 S/cm. We demonstrate that proton conductivity is maximized in high molecular weight, symmetric pNeh-b-pNpm copolymers.

We perform a joint experimental and computational study of ion transport properties in a systematic set of linear polyethers synthesized via acyclic diene metathesis (ADMET) polymerization. We measure ionic conductivity, σ, and glass transition temperature, Tg, in mixtures of polymer and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. While Tg is known to be an important factor in the ionic conductivity of polymer electrolytes, recent work indicates that the number and proximity of lithium ion solvation sites in the polymer also play an important role, but this effect has yet to be systematically investigated. Here, adding aliphatic linkers to a poly(ethylene oxide) (PEO) backbone lowers Tg and dilutes the polar groups; both factors influence ionic conductivity. To isolate these effects, we introduce a two-step normalization scheme. In the first step, Vogel–Tammann–Fulcher (VTF) fits are used to calculate a temperature-dependent reduced conductivity, σr(T), which is defined as the conductivity of the electrolyte at a fixed value of T – Tg. In the second step, we compute a nondimensional parameter fexp, defined as the ratio of the reduced molar conductivity of the electrolyte of interest to that of a reference polymer (PEO) at a fixed salt concentration. We find that fexp depends only on oxygen mole fraction, x0, and is to a good approximation independent of temperature and salt concentration. Molecular dynamics simulations are performed on neat polymers to quantify the occurrences of motifs that are similar to those obtained in the vicinity of isolated lithium ions. We show that fexp is a linear function of the simulation-derived metric of connectivity between solvation sites. From the relationship between σr and fexp we derive a universal equation that can be used to predict the conductivity of ether-based polymer electrolytes at any salt concentration and temperature.

Lithium sulfur batteries have a theoretical specific energy 5 times greater than current lithium ion battery standards, but suffer from the issue of lithium polysulfide dissolution. The reaction mechanisms that underlie the formation of lithium polysulfide reaction intermediates have been studied for over four decades, yet still elude researchers. Polysulfide radical anions formed during the redox processes have become a focal point of fundamental Li–S battery research. The formation of radical species has even been shown to be advantageous to the electrochemical pathways. However, whether polysulfide radical anions can form and be stabilized in common Li–S battery electrolytes that are ether-based is a point of contention in Li–S battery research. The goal of this work was to examine the presence of radical polysulfide species in ether-based solvents. Lithium polysulfide solutions in tetraethylene glycol dimethyl ether and poly(ethylene oxide) are probed using a combination of ultraviolet–visible (UV–vis) and electron paramagnetic resonance (EPR) spectroscopy. EPR results confirm the presence of radical species in ether-based electrolytes. Comparison of the UV–vis spectra to EPR spectra establishes that the UV–vis absorbance signature for radical species in ether-based solvents occurs at a wavelength of 617 nm, which is consistent with what is observed for high electron pair donor solvents such as dimethylformamide and dimethyl sulfoxide.

Despite high ionic conductivities, current inorganic solid electrolytes cannot be used in lithium batteries because of a lack of compliance and adhesion to active particles in battery electrodes as they are discharged and charged. We have successfully developed a compliant, nonflammable, hybrid single ion-conducting electrolyte comprising inorganic sulfide glass particles covalently bonded to a perfluoropolyether polymer. The hybrid with 23 wt% perfluoropolyether exhibits low shear modulus relative to neat glass electrolytes, ionic conductivity of 10−4 S/cm at room temperature, a cation transference number close to unity, and an electrochemical stability window up to 5 V relative to Li+/Li. X-ray absorption spectroscopy indicates that the hybrid electrolyte limits lithium polysulfide dissolution and is, thus, ideally suited for Li-S cells. Our work opens a previously unidentified route for developing compliant solid electrolytes that will address the challenges of lithium batteries.

Electrolytes consisting of low molecular weight perfluoropolyether (PFPE), poly(ethylene glycol) (PEG), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) blends were prepared and systematically studied for salt concentration and stoichiometry effects on the materials’ thermal and electrochemical properties. Herein we report that the tunable ratios of PFPE and PEG allow for precise control of crystalline melting and glass transition temperature properties. These blended liquid polymer electrolytes are inherently nonflammable and remain stable in the amorphous phase from approximately 150 °C down to −85 °C. The ionic conductivity of the electrolytes are on the order of 10–4 S/cm at 30 °C, which makes them suitable for rechargeable lithium batteries.

This is a study of the effect of copolymer composition on the electronic conductivity of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-b-PEO) block copolymers. A wide variety of P3HT-b-PEO block copolymers with P3HT volume fraction ranging from 0.28 to 0.86 were synthesized. Lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt was added to the P3HT-b-PEO copolymers to enable electrochemical oxidation. Three terminal electrochemical cells were used to oxidize the P3HT microphase; the two outer electrodes were used to oxidize P3HT, while a nickel mesh located within the P3HT-b-PEO enabled measurement of electronic conductivity by ac impedance. Symmetric block copolymers with P3HT volume fractions in the vicinity of 0.5 exhibited the highest electronic conductivity in the oxidized state. The symmetric copolymers also exhibited the highest crystallinity. The intrinsic conductivity of oxidized P3HT microphases increases exponentially with increasing crystallinity.

•We study block copolymer membranes for organic-water separation by pervaporation.•We compare permeabilities of different membranes.•Block copolymer membranes exhibit higher permeabilities than crosslinked membranes.•In situ product removal by pervaporation enables continuous fermentation.We address two major challenges facing commercialization of acetone–butanol–ethanol (ABE) fermentation: product inhibition and low productivity. We studied a polystyrene-b-polydimethylsiloxane-b-polystyrene (SDS) triblock copolymer membrane for selective removal of butanol from aqueous solutions by pervaporation. The SDS membrane exhibited higher permeabilities than a commercially available cross-linked polydimethylsiloxane (PDMS) membrane. Both types of pervaporation membrane were also used for in situ product removal of ABE biofuels in Clostridium acetobutylicum fermentations operated in a semi-continuous mode. Membrane performance and its effect on the fermentation process were assessed by measuring flux, OD600 and concentrations of different components in the fermenter as a function of time. Volumetric ABE productivity increased from 0.45 g/(L h) in simple batch fermentation to 0.66 g/(L h) in the case of pervaporative-fermentation with the PDMS membrane. A further increase in productivity to 0.94 g/(L h) was obtained in the case of pervaporative-fermentation with the SDS membrane. Overall, total ABE production improved by a factor of three, viable fermentation time increased by a factor of two, and cell density increased by a factor of 2.5 upon applying SDS membrane pervaporation, relative to the batch process.

Single-ion-conducting polymers are ideal electrolytes for rechargeable lithium batteries as they eliminate salt concentration gradients and concomitant concentration overpotentials during battery cycling. Here we study the ionic conductivity and morphology of poly(ethylene oxide)-b-poly(styrenesulfonyllithium(trifluoromethylsulfonyl)imide) (PEO-b-PSLiTFSI) block copolymers with no added salt using ac impedance spectroscopy and small-angle X-ray scattering. The PEO molecular weight was held fixed at 5.0 kg mol–1, and that of PSLiTFSI was varied from 2.0 to 7.5 kg mol–1. The lithium ion concentration and block copolymer composition are intimately coupled in this system. At low temperatures, copolymers with PSLiTFSI block molecular weights ≤4.0 kg mol–1 exhibited microphase separation with crystalline PEO-rich microphases and lithium ions trapped in the form of ionic clusters in the glassy PSLiTFSI-rich microphases. At temperatures above the melting temperature of the PEO microphase, the lithium ions were released from the clusters, and a homogeneous disordered morphology was obtained. The ionic conductivity increased abruptly by several orders of magnitude at this transition. Block copolymers with PSLiTFSI block molecular weights ≥5.4 kg mol–1 were disordered at all temperatures, and the ionic conductivity was a smooth function of temperature. The transference numbers of these copolymers varied from 0.87 to 0.99. The relationship between ion transport and molecular structure in single-ion-conducting block copolymer electrolytes is qualitatively different from the well-studied case of block copolymers with added salt.

We demonstrate that the water uptake and conductivity of proton-conducting block copolymer electrolyte membranes can be controlled systematically by the introduction of pores in the conducting domains. We start with a membrane comprising a mixture of homopolymer polystyrene (hPS) and a polystyrene-b-polyethylene-b-polystyrene (SES) copolymer. Rinsing the membranes in tetrahydrofuran and methanol results in the dissolution of hPS, leaving behind a porous membrane. The polystyrene domains in the porous SES membranes are then sulfonated to give a porous membrane with hydrophilic and hydrophobic domains. The porosity is controlled by controlling ϕv, the volume fraction of hPS in the blended membrane. The morphology of the membranes before and after sulfonation was studied by scanning transmission electron microscopy (STEM), electron tomography, and resonance soft X-ray scattering (RSoXS). The porous structures before and after sulfonation are qualitatively different. Water uptake of the sulfonated membranes increased with increasing ϕv. Proton conductivity is a nonmonotonic function of ϕv with a maximum at ϕv = 0.1. The introduction of microscopic pores in the conducting domain provides an additional handle for tuning water uptake and ion transport in proton-conducting membranes.

Transport of ions in polymer electrolytes is of significant practical interest, however, differences in the transport of anions and cations have not been comprehensively addressed. We present measurements of the electrochemical transport properties of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in poly(ethylene oxide) (PEO) over a wide range of PEO molecular weights and salt concentrations. Individual self-diffusion coefficients of the Li+ and TFSI– ions, D+ and D–, were measured using pulsed-field gradient nuclear magnetic resonance both in the dilute limit and at high salt concentrations. Conductivities calculated from the measured D+ and D– values based on the Nernst–Einstein equation were in agreement with experimental measurements reported in the literature, indicating that the salt is fully dissociated in these PEO/LiTFSI mixtures. This enables determination of the molecular weight dependence of the cation transference number in both dilute and concentrated solutions. We introduce a new parameter, s, the number of lithium ions per polymer chain, that allows us to account for both the effect of salt concentration and molecular weight on cation and anion diffusion. Expressing cation and anion diffusion coefficients as functions of s results in a collapse of D+ and D– onto a single master curve.

Hybrid nanostructured materials comprising block copolymers, nanoparticles, and lithium salts have the potential to serve as electrolytes in non-flammable rechargeable lithium batteries. Here we show that the addition of functionalized nanoparticles, at an optimized concentration, into lamellar block copolymer electrolytes, results in an increase in ionic conductivity. This is due to the occurrence of a lamellar-to-bicontinuous phase transition, driven by the addition of nanoparticles. The magnitude of the increase in conductivity is consistent with a simple model that accounts for the morphology of the conducting channels. The conductivity of the optimized hybrid electrolyte is only 6% lower than that of an idealized nanostructured electrolyte with perfectly connected conducting pathways and no dead ends.

Lithium–sulfur batteries are attractive due to their high theoretical specific energy, but the dissolution of lithium polysulfide intermediate species formed during discharge results in capacity fade and limited cycle life. In this study we present the first measurements of ionic conductivity of the polysulfides in a nanostructured block copolymer. The morphology, thermal properties, and the conductivities of polystyrene-b-poly(ethylene oxide) (SEO) containing lithium polysulfides, Li2Sx (x = 4, 8), were studied using small-angle X-ray scattering (SAXS), differential scanning calorimetry (DSC), and ac impedance spectroscopy. We also measured conductivities of mixtures of poly(ethylene oxide) (PEO) and Li2Sx. X-ray absorption spectroscopy was used to confirm the nature of dissolved polysulfides. SAXS measurements on SEO/Li2Sx mixtures indicated that all samples had a lamellar morphology. DSC measurements indicated that SEO/Li2S8 interactions were more favorable than SEO/Li2S4 interactions. The effect of nanostructure on transport of Li2Sx was quantified by calculating a normalized conductivity, which is proportional to the ratio of the conductivity of SEO/Li2Sx to that of the PEO/Li2Sx. The normalized conductivities of both polysulfides peaked at intermediate concentrations. The efficacy of block copolymer electrolytes in Li–S batteries was evaluated by comparing ionic conductivities of polymer electrolytes containing Li2Sx with those containing lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), a common salt used in PEO-based battery electrolytes. The transport of Li2Sx species in SEO is suppressed by factors ranging from 0.4 to 0.04 relative to LiTFSI, depending on x and salt concentration. To our knowledge, this study represents the first systematic investigation of the effect of molecular structure of polymer electrolytes on polysulfide migration.

Atomic level synthetic control over a polymer’s chemical structure can reveal new insights into the crystallization kinetics of block copolymers. Here, we explore the impact of side chain structure on crystallization behavior, by designing a series of sequence-defined, highly monodisperse peptoid diblock copolymers poly-N-decylglycine-block-poly-N-2-(2-(2-methoxyethoxy)ethoxy)ethylglycine (pNdc-b-pNte) with volume fraction of pNte (ϕNte) values ranging from 0.29 to 0.71 and polydispersity indices ≤1.00017. Both monomers have nearly identical molecular volumes, but the pNte block is amorphous while the pNdc block is crystalline. We demonstrate by X-ray scattering and calorimetry that all the block copolypeptoids self-assemble into lamellar microphases and that the self-assembly is driven by crystallization of the pNdc block. Interestingly, the microphase separated pNdc-b-pNte diblock copolymers form two distinct crystalline phases. Crystallization of the normally amorphous pNte chains is induced by the preorganization of the crystalline pNdc chains. We hypothesize that this is due to the similarity of chemical structure of the monomers (both monomers have linear side chains of similar lengths emanating from a polyglycine backbone). The pNte block remains amorphous when the pNdc block is replaced by another crystalline block, poly-N-isoamylglycine, suggesting that a close matching of the lattice spacings is required for induced crystallization. To our knowledge, there are no previous reports of crystallization of a polymer chain induced by microphase separation. These investigations show that polypeptoids provide a unique platform for examining the effect of intertwined roles of side chain organization on the thermodynamic properties of diblock copolymers.

Polymers that dissolve and conduct lithium ions are of great interest in the application of rechargeable lithium batteries. It is generally believed that the transport of ions in these systems is facilitated by rapid segmental motion typically found in rubbery, amorphous polymers. In this paper, we demonstrate that chemically identical ethyleneoxy-containing domains of a block copolymer exhibit comparable conductivities when in an amorphous or a crystalline state. An important feature of this study is the use of sequence-defined block copolypeptoids synthesized by submonomer solid-phase synthesis. Two structurally analogous ethyleneoxy-containing diblock copolypeptoids poly-N-(2-ethyl)hexylglycine-block-poly-N-2-(2-(2-methoxyethoxy)ethoxy)ethylglycine (pNeh-b-pNte) and poly-N-decylglycine-block-poly-N-2-(2-(2-methoxyethoxy)ethoxy)ethylglycine (pNdc-b-pNte) with 18 monomer units per block were synthesized. Both diblock copolypeptoids have the same conducting block, pNte, but different nonconducting blocks: pNeh, which is amorphous, and pNdc, which is crystalline. Both diblock copolypeptoids self-assemble into a lamellar morphology; however, pNte chains are amorphous in pNeh-b-pNte and crystalline in pNdc-b-pNte. This provides the platform for comparing lithium ion transport in amorphous and crystalline polymer domains that are otherwise similar.

The large-scale use of lignocellulosic hydrolysate as a fermentation broth has been impeded due to its high concentration of organic inhibitors to fermentation. In this study, pervaporation with polystyrene-block-polydimethylsiloxane-block-polystyrene (SDS) block copolymer membranes was shown to be an effective method for separating volatile inhibitors from dilute acid pretreated hydrolysate, thus detoxifying hydrolysate for subsequent fermentation. We report the separation of inhibitors from hydrolysate thermodynamically and quantitatively by detailing their concentrations in the hydrolysate before and after detoxification by pervaporation. Specifically, we report >99% removal of furfural and 27% removal of acetic acid with this method. Additionally, we quantitatively report that the membrane is selective for organic inhibitor compounds over water, despite water's smaller molecular size. Because its inhibitors were removed but its sugars left intact, pervaporation-detoxified hydrolysate was suitable for fermentation. In our fermentation experiments, Saccharomyces cerevisiae strain SA-1 consumed the glucose in pervaporation-detoxified hydrolysate, producing ethanol. In contrast, under the same conditions, a control hydrolysate was unsuitable for fermentation; no ethanol was produced and no glucose was consumed. This work demonstrates progress toward economical lignocellulosic hydrolysate fermentation.

A significant limitation of rechargeable lithium-ion batteries arises because most of the ionic current is carried by the anion, the ion that does not participate in energy-producing reactions. Single-ion-conducting block copolymer electrolytes, wherein all of the current is carried by the lithium cations, have the potential to dramatically improve battery performance. The relationship between ionic conductivity and morphology of single-ion-conducting poly(ethylene oxide)-b-polystyrenesulfonyllithium(trifluoromethylsulfonyl)imide (PEO–PSLiTFSI) diblock copolymers was studied by small-angle X-ray scattering and ac impedance spectroscopy. At low temperatures, an ordered lamellar phase is obtained, and the “mobile” lithium ions are trapped in the form of ionic clusters in the glassy polystyrene-rich microphase. An increase in temperature results in a thermodynamic transition to a disordered phase. Above this transition temperature, the lithium ions are released from the clusters, and ionic conductivity increases by several orders of magnitude. This morphology–conductivity relationship is very different from all previously published data on published electrolytes. The ability to design electrolytes wherein most of the current is carried by the lithium ions, to sequester them in nonconducting domains and release them when necessary, has the potential to enable new strategies for controlling the charge–discharge characteristics of rechargeable lithium batteries.

A systematic study of the dependence of ionic conductivity on the grain size of a lamellar block copolymer electrolyte was performed. A freeze-dried mixture of poly(styrene)-block-poly(ethylene oxide) and lithium bis(trifluoromethylsulfonyl)imide salt was heated in steps from 29 to 116 °C and then cooled back to 29 °C with an annealing time ranging from 30 to 60 min at each temperature. Grain structure and ionic conductivity during these steps were quantified by in situ small-angle X-ray scattering and ac impedance spectroscopy, respectively. Conductivity depends both on grain structure and temperature. A normalization scheme to decouple the dependence of conductivity on temperature and grain structure is described. Ionic conductivity at a given temperature was found to decrease by a factor of 5.2 ± 0.9 as the SAXS measure of grain size increased from 13 to 88 nm. The fact that in the system studied, large, well-formed lamellar grains are less conducting than poorly defined, small grains suggests a new approach for optimizing the transport properties of block copolymer electrolytes. Further work is necessary to confirm the generality of this finding.

Polyethylene, PE, is a crystalline solid with a relatively high melting temperature, and it exhibits excellent solvent resistance at room temperature. In contrast, polydimethylsiloxane, PDMS, is a rubbery polymer with an ultralow glass transition temperature and poor solvent resistance. PE–PDMS block copolymers have the potential to synergistically combine these disparate properties. In spite of this potential, synthesis of PE–PDMS block copolymers has not been widely explored. We report a facile route for the synthesis of well-defined polyethylene-b-polydimethylsiloxane-b-polyethylene (EDE) triblock copolymers. Poly(1,4-butadiene)-b-polydimethylsiloxane-b-poly(1,4-butadiene) (BDB) copolymer precursors were synthesized by anionic polymerization, followed by diimide-based hydrogenation. Under the standard hydrogenation conditions established by the work of Hahn, the siloxane bond undergoes scission resulting into significant degradation of the PDMS block. Our main accomplishment is the discovery of reaction conditions that avoid PDMS degradation. We used mechanistic insight into arrive at the optimal hydrogenation conditions, and we established the efficacy of our approach by successfully synthesizing a wide variety of block copolymers with total molecular weights ranging from 124 to 340 kg/mol and PDMS volume fractions ranging from 0.22 to 0.77.

Polymer electrolyte membranes with bicontinuous microphases comprising soft hydrated domains and mechanically robust hydrophobic domains are used in a wide range of electrochemical devices including fuel cells and electrolyzers. The self-assembly, water uptake, and proton conductivity of model block copolymer electrolytes with semicrystalline hydrophobic blocks were investigated. A series of sulfonated polystyrene-block-polyethylene (PSS–PE) copolymers were synthesized to probe the interplay between crystallization, morphology, hydration, and proton transport. In block copolymer systems with amorphous hydrophobic blocks, it has been shown that higher water update and proton conductivity are obtained in low molecular weight systems. However, crystallization is known to disrupt the self-assembly of low molecular weight block copolymers. We found that this disruption results in lower water uptake and proton conductivity. Increasing molecular weight results in less morphological disruption and improvement in performance.

Mixtures of block copolymers and lithium salts are promising candidates for lithium battery electrolytes. Structural changes that occur during the order-to-disorder transition (ODT) in a diblock copolymer/salt mixture were characterized by small-angle X-ray scattering (SAXS). In salt-free block copolymers, the ODT is sharp, and the domain size of the ordered phase decreases with increasing temperature. In contrast, the ODT of the diblock copolymer/salt mixture examined here occurs gradually over an 11 °C temperature window, and the domain size of the ordered phase is a nonmonotonic function of temperature. We present an approach to estimate the fraction of the ordered phase in the 11 °C window where ordered and disordered phases coexist. The domain spacing of the ordered phase increases with increasing temperature in the coexistence window. Both findings are consistent with the selective partitioning of salt into the ordered domains, as predicted by Nakamura et al. ( ACS Macro Lett. 2013, 2, 478−481).

Poly[(styrene)-block-((2-acryloxy)ethyltributylphosphonium bromide)] diblock copolymers (STBP) were synthesized in two steps. First, reversible addition–fragmentation chain transfer polymerization was used to synthesize the diblock copolymer precursors poly[(styrene)-block-(bromoethyl acrylate)] (SBEA), followed by functionalization with tributylphosphine. Copolymers with overall molecular weights ranging from 31 to 87 kg/mol were synthesized. The volume fraction of the ion-containing monomers in the copolymers was fixed at about 0.57. Self-assembly of these copolymers into ordered morphologies with tunable domain sizes was demonstrated by small-angle X-ray scattering. The effect of morphology on water uptake and bromide ion conductivity was explored in samples equilibrated in liquid water. The use of the pendant tributylphosphonium cations, which have some hydrophobic character, results in low water uptake and high anionic conductivity. The conductivity increases with increasing domain size while water uptake is unaffected by domain size.

Small-angle neutron scattering (SANS) was used to probe the phase behavior of multicomponent mixtures of supercritical carbon dioxide (scCO2), styrene–acrylonitrile random copolymer, and deuterated poly(methyl methacrylate). Ternary mixtures were homogeneous at low carbon dioxide pressures (PCO2) but phase separated as PCO2 was increased at constant temperature (T). Phase separation pressure was found to be a nonmonotonic function of T with a minimum at T = 60 °C. An expression based on the multicomponent random phase approximation was used to determine the interaction parameters between polymer and scCO2 from a combination of SANS experiments on homogeneous ternary mixtures and measurements of scCO2 uptake by the neat polymers. Interaction parameters that underlie the nonmonotonic phase behavior described above collapse onto a straight line when plotted as a function of scCO2 density.

The flammability of conventional alkyl carbonate electrolytes hinders the integration of large-scale lithium-ion batteries in transportation and grid storage applications. In this study, we have prepared a unique nonflammable electrolyte composed of low molecular weight perfluoropolyethers and bis(trifluoromethane)sulfonimide lithium salt. These electrolytes exhibit thermal stability beyond 200 °C and a remarkably high transference number of at least 0.91 (more than double that of conventional electrolytes). Li/LiNi1/3Co1/3Mn1/3O2 cells made with this electrolyte show good performance in galvanostatic cycling, confirming their potential as rechargeable lithium batteries with enhanced safety and longevity.

This is a study of morphology, water uptake, and proton conductivity of a sulfonated polystyrene-block-polyethylene (PSS-PE) copolymer equilibrated in humid air with controlled relative humidity (RH), and in liquid water. Extrapolation of the domain size, water uptake, and conductivity obtained in humid air to RH = 100% allowed for an accurate comparison between the properties of PSS-PE hydrated in saturated vapor and in liquid water. We demonstrate that extrapolations of domain size and water uptake on samples equilibrated in humid air are consistent with measurements on samples equilibrated in liquid water. Small (5%) differences in proton conductivity were found in samples equilibrated in humid air and liquid water. We argue that differences in transport coefficients in disordered heterogeneous systems, particularly small differences, present no paradox whatsoever. Schroeder’s Paradox, wherein properties of polymers measured in saturated water vapor are different from those obtained in liquid water, is thus not observed in the PSS-PE sample.

Ion-containing block copolymers are of interest for applications such as electrolytes in rechargeable lithium batteries. The addition of salt to these materials is necessary to make them conductive; however, even small amounts of salt can have significant effects on the phase behavior of these materials and consequently on their ion-transport and mechanical properties. As a result, the effect of salt addition on block copolymer thermodynamics has been the subject of significant interest over the past decade. This feature article describes a comprehensive study of the thermodynamics of block copolymer/salt mixtures over a wide range of molecular weights, compositions, salt concentrations, and temperatures. The Flory–Huggins interaction parameter was determined by fitting small-angle X-ray scattering data of disordered systems to predictions based on the random phase approximation. Experiments on neat block copolymers revealed that the Flory–Huggins parameter is a strong function of chain length. Experiments on block copolymer/salt mixtures revealed a highly nonlinear dependence of the Flory–Huggins parameter on salt concentration. These findings are a significant departure from previous results and indicate the need for improved theories for describing thermodynamic interactions in neat and salt-containing block copolymers.

Microphase-separated block copolymer materials have a wide array of potential applications ranging from nanoscale lithography to energy storage. Our understanding of the factors that govern the morphology of these systems is based on comparisons between theory and experiment. The theories generally assume that the chains are perfectly monodisperse; however, typical experimental copolymer preparations have polydispersity indices (PDIs) ranging from 1.01 to 1.10. In contrast, we present a systematic study of the relationship between chemical structure and morphology in the solid state using peptoid diblock copolymers with PDIs of ≤1.00013. A series of comb-like peptoid block copolymers, poly(N-2-(2-(2-methoxyethoxy)ethoxy)ethylglycine)-block-poly(N-(2-ethylhexyl)glycine) (pNte-b-pNeh), were obtained by solid-phase synthesis. The number of monomers per chain was held fixed at 36, while the volume fraction of the Nte block (ϕNte) was varied from 0.11 to 0.65. The experimentally determined order–disorder transition temperature exhibited a maximum at ϕNte = 0.24, not ϕNte = 0.5 as expected from theory. All of the ordered phases had a lamellar morphology, even in the case of ϕNte = 0.11. Our results are in qualitative disagreement with all known theories of microphase separation in block copolymers. This raises new questions about the intertwined roles of monomer architecture and polydispersity in the phase behavior of diblock copolymers.

Quantitative analysis of small angle neutron scattering (SANS) data from homogeneous multicomponent mixtures of supercritical carbon dioxide (scCO2) and two polymers is presented for the first time. The two polymers used in this study were styrene-acrylonitrile copolymer (SAN) and deuterated poly(methyl methacrylate) (dPMMA). Model polymers were used to facilitate comparisons between theory and experiment. The random phase approximation (RPA) was used to derive a simple expression to describe SANS profiles. The scCO2-free binary blend was studied to determine the temperature dependence of the polymer–polymer interaction parameter. scCO2-polymer solubility data was used to relate polymer–solvent interaction parameters. Comparisons between SANS profiles from multicomponent mixtures and the RPA expression provided an estimate of the interaction parameter between scCO2 and PMMA, χ13. The addition of scCO2 at a modest pressure results in a decrease of phase separation temperature Ts by 127 K. The analysis indicates that the change in Ts is caused by an increase in χ13 with increasing scCO2 pressure.

A series of poly(styrene-b-dimethylsiloxane-b-styrene) (SDS) triblock copolymers with molecular weights ranging from 55 to 150 kg/mol and polydimethylsiloxane (PDMS) volume fractions ranging from 0.59 to 0.83 were used to fabricate membranes for ethanol/water separation by pervaporation. The rigid polystyrene (PS) microphase provides the membrane with structural integrity, while the rubbery PDMS microphase provides nanoscale channels for ethanol transport. We use a simple model to study the effect of morphology and PDMS volume fraction on permeabilitites of ethanol and water through the block copolymer membranes. We defined normalized permeabilities of ethanol and water to account for differences in morphology and PDMS volume fraction. We found that the normalized ethanol permeability in SDS copolymers was independent of the total polymer molecular weight. This is qualitatively different from what was previously reported for poly(styrene-b-butadiene-b-styrene) (SBS) membranes, where the normalized ethanol permeability was found to be a sensitive function of total molecular weight [J. Membr. Sci. 2011, 373, 112]. We demonstrate that this is due to differences in the Flory–Huggins interaction parameter (χ) for the two systems. When χN is less than 100 (N is the number of segments per chain), the two microphases are weakly segregated, and the presence of glassy PS segments in the transporting microphase impedes ethanol transport. When χN exceeds 100, the two microphases are strongly segregated and the glassy PS segments do not mix with the transporting phase. We compare these results with normalized ionic conductivity data previously reported for mixtures of a lithium salt and polystyrene-b-poly(ethylene oxide) (SEO). Evidence suggests that the product χN governs the transport of widely different species such as ethanol and lithium salts through block copolymer membranes. Surprisingly, the normalized permeability of water is independent of total molecular weight for both SDS and SBS block copolymers.

Polystyrene-block-polyethylene-block-polystyrene (SES) copolymers were blended with homopolymer polystyrene (PS), and films of the blend were solvent cast using a doctor blade. The nonporous SES and PS films were exposed to both tetrahydrofuran (THF) and methanol (MeOH) in an alternating fashion for 1 min intervals three times, without letting the films dry between solvent immersions. At this point, either the films were removed from MeOH and dried or the films were immersed in THF and then dried. THF is a nonsolvent for crystalline polyethylene (PE) but a good solvent for both amorphous PE and PS. Methanol is a nonsolvent for semicrystalline PE, amorphous PE, and PS. Films that were dried with MeOH as the final nonsolvent were highly porous and exhibited high conductivity when swollen in a liquid electrolyte. In contrast, films that were dried with THF as the final nonsolvent were nonporous and exhibited poor conductivity when swollen in a liquid electrolyte. We study the fundamental effect of nonsolvent exposure on film properties using electron microscopy, nitrogen physisorption, and X-ray scattering techniques.

Anion-conducting membranes are important for several applications including fuel cells and artificial photosynthesis. In this study such membranes were made by quaternizing polystyrene-block-polychloromethylstyrene (PS-b-PCMS) copolymers. PS-b-PCMS copolymers with molecular weights ranging from 4 to 60 kg/mol were synthesized by nitroxide-mediated controlled radical polymerization. Separate aliquots of the PS-b-PCMS samples were quaternized to transform the PCMS block. This resulted in block copolymers with ionizable blocks containing either trimethylammonium chloride or n-butylimidazolium chloride. We refer to ion-containing block copolymers synthesized from the same precursor as matched pairs: SAM (containing trimethylammonium chloride) and SIM (containing n-butylimidazolium chloride). The volume fraction of the ion-containing block, ϕ, ranges from 0.26 to 0.50 for the case of SAM and from 0.35 to 0.60 for the case of SIM. Self-assembly in these copolymers resulted in the formation of lamellar phases regardless of ϕ, chemical formula of the bound ion, and chain length. Chloride ion conductivity and water uptake measurements on one of the matched pairs led to similar results. Preliminary experiments wherein the chloride ions in this matched pair were replaced by hydroxide ions were performed, and the changes in conductivity due to this are reported.

Block copolymers that can simultaneously conduct electronic and ionic charges on the nanometer length scale can serve as innovative conductive binder material for solid-state battery electrodes. The purpose of this work is to study the electronic charge transport of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT-PEO) copolymers electrochemically oxidized with lithium bis(trifluoromethanesulfonyl) imide (LiTFSI) salt in the context of a lithium battery charge/discharge cycle. We use a solid-state three-terminal electrochemical cell that enables simultaneous conductivity measurements and control over electrochemical doping of P3HT. At low oxidation levels (ratio of moles of electrons removed to moles of 3-hexylthiophene moieties in the electrode), the electronic conductivity (σe,ox) increases from 10–7 S/cm to 10–4 S/cm. At high oxidation levels, σe,ox approaches 10–2 S/cm. When P3HT-PEO is used as a conductive binder in a positive electrode with LiFePO4 active material, P3HT is electrochemically active within the voltage window of a charge/discharge cycle. The electronic conductivity of the P3HT-PEO binder is in the 10–4 to 10–2 S/cm range over most of the potential window of the charge/discharge cycle. This allows for efficient electronic conduction, and observed charge/discharge capacities approach the theoretical limit of LiFePO4. However, at the end of the discharge cycle, the electronic conductivity decreases sharply to 10–7 S/cm, which means the “conductive” binder is now electronically insulating. The ability of our conductive binder to switch between electronically conducting and insulating states in the positive electrode provides an unprecedented route for automatic overdischarge protection in rechargeable batteries.Keywords: conducting polymers; electrochemical oxidation; electronic conductivity; ionic conductivity; lithium battery; mixed conductor; overdischarge protection

We report on the synthesis and morphology of a block copolymer, poly(3-(2′-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO), that conducts both electrons and ions. We show that in the melt state the P3EHT-b-PEO chains self-assemble to produce traditional nanoscale morphologies such as lamellae and gyroid. This is in contrast to a majority of previous studies on copolymers with electronically conducting blocks wherein a nanofibrillar morphology is obtained. Our approach enables estimation of the Flory–Huggins interaction parameter, χ. The segregation strength between the two blocks is controlled through the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). For the salt-free sample, the gyroid morphology, obtained in the melt state, is transformed into lamellae below the melting temperature of the P3EHT block. This is due to the “breaking out” of the crystalline phase. For the salt-containing sample, P3EHT-b-PEO has a lamellar morphology in both melt and crystalline states (confined crystallization).

Nanoporous battery separators were made by blending a polystyrene-block-polyethylene-block-polystyrene copolymer (SES) and polystyrene (PS) homopolymers, casting films of the blend, and selectively dissolving the homopolymer. The efficacy of the separators thus obtained was determined by measurement of the ionic conductivity of separators soaked in 1 M lithium hexafluorophosphate in ethylene carbonate/diethyl carbonate (1:1, v/v, Novolyte Technologies, Inc.), a standard lithium battery electrolyte. We focus on the effect of chain length of the sacrificial homopolymer on separator morphology and ion transport. In highly porous separators with a nominal pore volume fraction of 0.43, conductivity peaked at α = 0.22, where values as high as 0.39 mS cm−1 were achieved (α is the molecular weight of the PS homopolymer normalized by that of the PS block in the SES copolymer). Nitrogen adsorption experiments and scanning electron microscopy were used to determine the underpinnings of this observation. At α = 0.12, extremely small pores with low surface area are formed. Increasing α to 0.22 results in a film with well-connected nanoscale pores. A further increase in α to 2.02 results in films with micron-sized pores that are not effective for ion transport.Highlights► Battery separators were made by block copolymer/homopolymer blends. ► Pores were made by selective removal of homopolymer. ► Morphology and conductivity were found to depend on homopolymer molecular weight. ► Conductivities obtained were comparable to commercial Celgard® 2400 membranes.

We report on the effect of changing nanoscale morphology on pervaporation of ethanol/water mixtures through block copolymer membranes. Experiments were conducted using polystyrene-b-polybutadiene-b-polystyrene (SBS) copolymers with polybutadiene (PB) as the ethanol transporting block, using an 8 wt% ethanol/water mixture as the feed. The volume fraction of the transporting PB microphase, ϕPB, was varied from 0.63 to 0.93, and the overall molecular weight of the copolymer, Mn, was varied from 34 to 207 kg mol−1. The normalized ethanol permeability through the membrane, PE/ϕPB, and the ethanol selectivity, αEW, increase with increasing Mn. In the case of ϕPB = 0.73 and 0.80 systems (cylindrical morphologies), PE/ϕPB and αEW appear to reach a plateau in the high Mn limit. Master curves are obtained when all of the permeation data are plotted in the PE/ϕPB and PW/ϕPB versus αEW format. The performance of the SBS membrane with Mn = 207 kg mol−1 and ϕPB = 0.80 is tested using a fermentation broth mixture.Graphical abstractHighlights► Selective ethanol transport through nanostructured block-copolymer membranes. ► Transport and structural components decoupled. ► Permeability and selectivity improve with increasing molecular weight for all morphologies. ► Normalized permeability versus selectivity generates master plots.

The ionic conductivity of a block copolymer electrolyte was measured in an in situ small-angle X-ray scattering experiment as it transitioned from an ordered lamellar structure to a disordered phase. The ionic conductivity increases discontinuously as the electrolyte transitions from order to disorder. A simple framework for quantifying the magnitude of the discontinuity is presented. This study lays the groundwork for understanding the effect of more complex phase transitions such as order–order transitions on ion transport.

Nanoscale ionic aggregates are ubiquitous in copolymers containing charged and uncharged monomers. In most cases, these clusters persist when these polymers are hydrated and ion-conducting channels percolate through the sample. We argue that these clusters impede ion motion due to (1) the requirement that ions must hop across ion-free regions in the channels as they are transported from one cluster to the next, and (2) increased counterion condensation due to proximity of fixed acid groups in the clusters. Block copolymers wherein the size of the ion-containing microphase is 6 nm or less provides one approach for eliminating the clusters.

We demonstrate the use of contrast-matched resonant soft X-ray scattering (RSoXS) for studying the morphology of mesoporous polystyrene-block-polyethylene-block-polystyrene (SES) copolymer membranes. The mesoporous membranes were obtained by blending the SES copolymer and polystyrene (PS) homopolymer to obtain a nonporous membrane, followed by selective dissolution of the PS. If the PS homopolymer chains are initially located within the PS microphase of the SES copolymer, then one obtains a porous film wherein the pores are lined with PS. We refer to this as the templated morphology. The membranes are thus composed of three phases: voids, PS, and PE. Conventional techniques such as small-angle X-ray scattering (SAXS) and scanning electron microscopy (SEM) only distinguish between the polymer and the voids. The main advance in this paper is to show that microphase separation between PS and PE can be studied by contrast-matched RSoXS in spite of the presence of voids. Under certain circumstances, we obtain mesoporous membranes that are not templated by the SES copolymer. We show that RSoXS can be used to distinguish between templated and nontemplated, mesoporous films.

We present a procedure for creating samples that can be repeatedly cycled between weakly aligned and strongly aligned states. Poly(styrene-b-isoprene) block copolymer samples were first shear-aligned and then cross-linked using a high energy electron beam. Samples with more than 1.0 cross-links per chain on average showed almost complete recovery of their initial alignment state even after 20 cycles of heating above the order–disorder transition temperature of the un-cross-linked block copolymer. Samples with 1.1 cross-links per chain, which showed over 90% loss of alignment on heating and almost 100% recovery of alignment on cooling, provided the best example of a reversible aligned-to-unaligned transition. Samples with lower cross-linking densities exhibited irreversible loss of alignment upon heating, while those with higher cross-linking densities exhibited less than 90% loss of alignment upon heating. Alignment was quantified by a technique that we call two color depolarized light scattering (TCDLS), an extension of the traditional depolarized light scattering experiment used to determine the state of order in block copolymers. Qualitative confirmation of our interpretation of TCDLS data was obtained by small-angle X-ray scattering and transmission electron microscopy.

The main objective of this work is to study charge transport in mixtures of poly(3-hexylthiophene)-b-poly(ethylene oxide) (P3HT–PEO) block copolymers and lithium bis(trifluoromethanesulfonyl) imide salt (LiTFSI). The P3HT-rich microphase conducts electronic charge, while the PEO-rich microphase conducts ionic charge. The nearly symmetric P3HT–PEO copolymer used in this study self-assembles into a lamellar phase. In contrast, the morphologies of asymmetric copolymers with P3HT as the major component are dominated by nanofibrils. A combination of ac and dc impedance measurements was used to determine the electronic and ionic conductivities of our samples. The ionic conductivities of P3HT–PEO/LiTFSI mixtures are lower than those of mixtures of PEO homopolymer and LiTFSI, in agreement with published data obtained from other block copolymer/salt mixtures. In contrast, the electronic conductivities of the asymmetric P3HT–PEO copolymers are significantly higher than those of the P3HT homopolymer. This is unexpected because of the presence of the nonelectronically conducting PEO microphase. This implies that the intrinsic electronic conductivity of the P3HT microphase in P3HT–PEO copolymers is significantly higher than that of P3HT homopolymers.Keywords: ac impedance; block copolymers; conducting polymers; electronic conductivity; ionic conductivity; mixed conductors

There is considerable interest in the properties of polymer electrolyte membranes due to their presence in fuel cells. In this paper, we report on the ionic conductivity and degree of hydration, λ, of model membranes composed of polystyrene sulfonate-b-polymethylbutylene (PSS–PMB) copolymers and their imidazolium salts (PSI–PMB). The membranes were in intimate contact with humid air, and their properties were studied as a function of temperature and relative humidity of the air (RH = 50 and 98%). All of the samples have a lamellar structure in the dry state, and λ = 14 ± 2 for PSS–PMB and PSI–PMB at RH = 98%. However, the conductivity behaviors of PSS–PMB and PSI–PMB are very different. The normalized conductivity, σn (the normalization accounts for small differences in the ion concentrations in the different samples), of PSS–PMB is highly history-dependent and equilibrated behavior is only seen when the samples are annealed at high temperature (80 °C) for long times (about 24 h). In contrast, the equilibrated behavior is obtained rapidly in PSI–PMB samples over the entire temperature window (25–90 °C). At RH = 98%, the equilibrated conductivities of the PSI–PMB samples at RH = 98% were independent of sample molecular weight and within the experimental error of that obtained from the high molecular weight PSS–PMB sample. The low molecular weight PSS–PMB sample exhibited higher conductivity than the three samples described above. At RH = 50% both PSS–PMB and PSI–PMB samples were relatively dry with λ < 5 over the accessible temperature window. In the dry state (1) PSS–PMB samples exhibited slow kinetics while PSI–PMB samples equilibrated rapidly, (2) molecular weight had no effect on conductivity in both PSS–PMB and PSI–PMB samples, and (3) the conductivities of PSI–PMB were significantly lower than those of PSS–PMB.

We review the literature on proton conductivity and water uptake of composite polymer electrolyte membranes comprising bicontinuous hydrophilic and hydrophobic domains with well-controlled geometries. Both quantities appear to be enhanced when the width of the hydrophilic channels is smaller than 6 nm.Figure optionsDownload full-size imageDownload as PowerPoint slide

Phase diagrams of four binary blends of polyisobutylene (component 1) and deuterated polybutadiene (component 2) were determined using small-angle neutron scattering (SANS). Our study covers N1/N2 values ranging from 0.23 to 0.92 and Ni ranging from about 800 to 3600 (Ni is the number of monomers per chain of component i based on a reference volume = 0.1 nm3). The experimentally determined binodal curves were in good agreement with the predictions based on the Flory−Huggins theory using a previously determined composition- and chain-length-dependent Flory−Huggins interaction parameter presented in Nedomaet al. Macromolecules 2008, 41, 5773−5779. The experimentally determined spinodal curves, which were surprisingly close to the experimental binodal curves, deviated significantly from predictions, an observation for which we offer no quantitative explanation.

Nafion(117) membranes in contact with acidic solutions were characterized by small-angle X-ray scattering and by acid solution uptake measurements. The principle of Donnan equilibrium was used to obtain independent estimates of the extent of counterion condensation in the membranes from the three experiments. The surprising conclusion of our study is that a large fraction of the protons in Nafion are in the condensed form when the membrane is immersed in pure water. Estimates of the fraction of condensed protons range from 72 to 98%.

Lithium polysulfides (Li2Sx, 1 ≤ x ≤ 8) are produced during the discharge of lithium–sulfur batteries. Lithium–sulfur batteries are of interest due to their high energy density. The morphology of mixtures of polystyrene-b-poly(ethylene oxide) (SEO) copolymers and lithium polysulfides were studied using a combination of X-ray diffraction, small-angle X-ray scattering, differential scanning calorimetry, and ultraviolet–visible spectroscopy. This study is motivated by the possibility of using block copolymers as electrolytes in lithium–sulfur cells. The phase behavior of SEO/Li2Sx mixtures were found to differ fundamentally from mixtures of SEO and other lithium salts. The morphology of certain SEO/Li2Sx mixtures obtained below the melting temperature of the poly(ethylene oxide) block has not been previously observed in block copolymer/salt mixtures.

The ionic conductivity, σ, of mixtures of poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfone)imide (LiTFSI) was measured as a function of molecular weight of the PEO chains, M, over the range 0.2–5000 kg/mol. Our data are consistent with an expression σ = σ0 + K/M proposed by Shi and Vincent [Solid State Ionics 60 (1993)] where σ0 and K are exponential and linear functions of inverse temperature respectively. Explicit expressions for σ0 and K are provided.Highlights► PEO/LiTFSI electrolyte conductivity measured over wide molecular weight range ► Conductivity contributions arise from both segmental motion and chain diffusion. ► Explicit expressions provided for molecular weight dependence of conductivity

Proton conductivity (σ) and degree of hydration (λ) of poly(styrenesulfonate−methylbutylene) (PSS−PMB) block copolymers in contact with humid air were studied as a function of temperature under high-humidity conditions (relative humidity between 90 and 98%). The volume fraction of the hydrophilic PSS block in the dry state was 0.27 ± 0.01 in all of the samples, and the size of the hydrophilic channels was varied by varying the overall molecular weight of the samples. All of the samples have a lamellar structure in the dry state. The water uptake data were unremarkable, and a degree of hydration of 14 ± 2 H2O molecules per sulfonic acid group was obtained, regardless of temperature, thermal history, and hydrophilic channel size. In contrast, measured values of σ were highly dependent on thermal history and sample molecular weight. Equilibrated values of σ, obtained only after heating the samples to 90 °C for 48 h, were significantly lower than those obtained after initially hydrating the polymer films during the heating runs. In addition, the low molecular weight samples were more sensitive to thermal history than the high molecular weight samples. Small-angle neutron scattering and transmission electron microscopy studies on the humidified samples revealed that the low molecular weight samples undergo a transition to hexagonally perforated lamellae upon hydration while the highest molecular weight sample did not. We speculate that the slow changes in σ are due to the formation of less connected ion transporting channels or ionic clusters that impede ion motion. Equilibrated ionic conductivities increase as the hydrophilic channel size decreases.

Small-angle neutron scattering (SANS) was used to study the phase behavior of A/B/A−C blends wherein A and B were immiscible homopolymers and A−C was an amphiphilic diblock copolymer. A series of blends were prepared with a fixed diblock copolymer volume fraction of 0.40, and the volume fraction of A homopolymer was varied from 0.1 to 0.5. All blends exhibited the same quantitative phase behavior despite differences in blend composition: lamellae below 115 °C and macrophase separation above 122 °C. Least-squares fits of the SANS data below 115 °C were used to extract information about the A-rich and B-rich lamellae using a model for randomly oriented lamellae developed by Hosemann and Bagchi. Our approach explicitly accounts for the concentration fluctuations within the lamellae using the random phase approximation. The results of the analysis were found to agree with predictions calculated using self-consistent-field theory (SCFT) with no adjustable parameters. The experimentally determined transitions from lamellae to macrophase separation were also in good agreement with SCFT. Calculations based on multicomponent RPA predicted a small homogeneous window that was not experimentally observed in any of the blends studied.

Small angle neutron scattering is used to study the phase behavior of mixtures of two immiscible homopolymers (A and B) and a diblock copolymer (A−C) wherein B and C chains exhibit attractive interactions (negative Flory−Huggins interaction parameter) and the other pairs of chains exhibit repulsive interactions. This study explores the effect of homopolymer molecular weight asymmetry (NA/NB ≠ 1, where NI is the number of monomer units per chain in homopolymer I) at fixed segregation strength of the homopolymers. The temperature windows over which lamellae, microemulsions, macrophase separation, and homogeneous phases are found are affected qualitatively by NA/NB. In particular, a homogeneous window that was not present in symmetric A/B/A−C blends is seen when NA/NB exceeds a critical value.

The distribution of an ionic liquid within microphase-separated domains of a block copolymer in mixtures of the two components is studied using contrast-matched small-angle neutron scattering (SANS) and differential scanning calorimetry (DSC). In concentrated mixtures of a poly(styrene-block-2-vinyl pyridine) (S2VP) copolymer in an imidazolium bis(trifluoromethane)sulfonimide ([Im][TFSI]) ionic liquid (block copolymer volume fraction ranging from 0.51 to 0.86), the ionic liquid preferentially pervades the poly(2-vinyl pyridine) (P2VP) blocks. Unexpected differences in the degree of partitioning into P2VP-rich and polystyrene-rich (PS) microphases are observed in mixtures with hydrogenated versus deuterated [Im][TFSI]. In the case of mixtures with hydrogenated [Im][TFSI], the microphase partition coefficient, defined as the ratio of the ionic liquid volume fraction in the PS-rich microphase relative to that in the P2VP-rich microphase, ranges from 0.0 to 0.1. In contrast, the microphase partition coefficient in mixtures with deuterated [Im][TFSI] range from 0.0 to 0.7.

The effect of alignment of proton-conducting domains in hydrated poly(styrenesulfonate-b-methylbutylene) copolymer films on conductivity was studied by impedance spectroscopy. Pressing isotropic samples obtained by casting results in lamellae aligned in the plane of the film. Application of electric fields and flow fields on the isotropic samples results in lamellae aligned perpendicular to the plane of the film. The alignment of lamellae, quantified by a combination of two dimensional small angle X-ray scattering (SAXS), birefringence, and transmission electron microscopy (TEM), was much better in the pressed samples than in the field-aligned samples. Conductivity was measured in the plane of the film (σ∥) and normal to the plane of the film (σ⊥). Only the pressed sample showed highly anisotropic proton conduction with σ∥/σ⊥ = 75. In this case, the value of σ∥ increased by 30% after alignment, relative to that obtained from the as-cast samples. The values of σ∥/σ⊥ obtained after electric field and shear field alignment were 1.2 and 1.4, respectively, in spite of partial alignment of the domains, and the increase in σ⊥ after alignment was less than 20%.

The phase behavior of poly(styrene-block-2-vinylpyridine) copolymer solutions in an imidazolium bis(trifluoromethane)sulfonamide ([Im][TFSI]) ionic liquid has been studied using small-angle X-ray scattering (SAXS) and optical transmission characterization. Through scaling analysis of SAXS data, we demonstrate that the [Im][TFSI] ionic liquid behaves as a selective solvent toward one of the blocks. We observe lyotropic and thermotropic phase transitions that correspond qualitatively to the phase behavior observed in block copolymer melts and block copolymer solutions in molecular solvents. In addition, we have studied the thermal properties of block copolymer solutions in the ionic liquid using differential scanning calorimetry and wide-angle X-ray scattering. We observe distinct composition regimes corresponding to the change in the block copolymer’s glass transition temperature, Tg, with respect to the concentration of polymer in ionic liquid. At high block copolymer concentrations, a “salt-like” regime corresponding to an increase in the block copolymer Tg is observed, while at intermediate block copolymer concentrations, a “solvent-like” regime corresponding to a decrease in the block copolymer Tg is observed. An unusual thermal transition consisting of crystallization and subsequent melting of the ionic liquid is observed at the lowest block copolymer concentration characterized.

The phase behavior of binary blends of polyolefins is studied using small-angle neutron scattering. Component 1 is polyisobutylene (PIB), and component 2 is deuterated polybutadiene (dPB). Blends of these polymers are known to exhibit lower critical solution temperatures. The scattering intensity profiles from homogeneous PIB/dPB blends are fit to the random phase approximation to determine χ, the Flory−Huggins interaction parameter. We demonstrate that χ depends on temperature, blend composition, and component molecular weights.