Co-reporter:Siyao He, Yuqiang Qian, Kunwei Liu, Christopher W. Macosko, and Andreas Stein
Industrial & Engineering Chemistry Research October 11, 2017 Volume 56(Issue 40) pp:11443-11443
Publication Date(Web):September 14, 2017
DOI:10.1021/acs.iecr.7b02583
Incorporating graphene-based nanomaterials into thermosetting resins is challenging at an industrial-scale. To address this issue, we prepared a styrene masterbatch containing chemically modified graphene oxide (mGO) and added it to unsaturated polyester and vinyl ester resins via simple mechanical mixing to generate homogeneous mGO/resin dispersions. For comparison, oven-dried or freeze-dried mGO was also blended into resin using the same mechanical mixing conditions. At low mGO loading levels of 0.02–0.08 wt %, composites made with oven-dried or freeze-dried mGO show the highest increase in fracture toughness but also the most severe decrease in flexural strength, whereas composites prepared from the mGO masterbatch show the best dispersion homogeneity and better retention of flexural strength while exhibiting only slightly less increase in toughness. The masterbatch process offers an economical way of producing high-quality mGO/resin dispersions.
Co-reporter:Siyao He, Nicholas D. Petkovich, Kunwei Liu, Yuqiang Qian, Christopher W. Macosko, Andreas Stein
Polymer 2017 Volume 110(Volume 110) pp:
Publication Date(Web):10 February 2017
DOI:10.1016/j.polymer.2016.12.057
•Graphene oxide (GO) was modified with alkyl and reactive vinyl functional groups.•Functionalized GO is easily dispersible in unsaturated polyester resin (UPR).•Fracture toughness is significantly improved at very low loading of modified GO.•Modulus of UPR composite with modified GO remains nearly unchanged.•Modified GO toughens the UPR resin by crack pinning and particle-matrix bonding.Graphene oxide (GO) and its derivatives with vinyl and alkyl functional groups (mGO) were synthesized and dispersed into unsaturated polyester resin (UPR) to prepare nanocomposites. Successful chemical modification of the GO sheets was confirmed by infrared spectroscopy, thermogravimetric analysis, and X-ray diffraction. In contrast to unmodified GO, mGO was easily dispersed in UPR, even without sonication, making the process scalable. The few-micrometer GO sheets and aggregates in the resin composite were characterized by transmission electron microscopy and visible light microscopy. Compact tension testing of the resin composites with mGO showed that, with a remarkably low loading of only 0.04 wt% mGO, a 55% improvement in fracture energy (GIC) was obtained with little change in flexural strength or modulus. This high effectiveness renders mGO economically viable. Analysis of fracture surfaces by scanning electron microscopy suggests that mGO particles interact with the propagating crack, the main toughening effect being crack pinning.Download high-res image (172KB)Download full-size image
Co-reporter:Yuewen Xu, Paula Delgado, Alexander D. Todd, Jesse Loi, Stacey A. Saba, Ryan J. McEneany, Ted Tower, Vasily Topolkaraev, Christopher W. Macosko, Marc A. Hillmyer
Polymer 2016 Volume 102() pp:73-83
Publication Date(Web):12 October 2016
DOI:10.1016/j.polymer.2016.08.102
•Lightweight PLA/polyolefin blends are produced.•Micro-cellular structures are formed during cold-drawn of polymers.•The blend material consists of majority of bio-degradable polylactide.Semi-crystalline polylactide (PLA)/polyolefin multi-component blends were used as precursors for the generation of a new class of micro-cellular polymers. Either a polypropylene-based elastomer (PBE) or polypropylene (PP) homopolymer were utilized as dispersed phases at the 10 wt% level. An epoxy-functionalized terpolymer (PEGMMA) was introduced (1 wt%) as a reactive compatibilizer to reduce the dispersed phase droplet size and provide sufficient adhesion between the matrix and dispersed phase. In addition, a polyalkylene glycol liquid (PAG) was added to the blend (4 wt%) to serve as a PLA plasticizer and interfacial modifier. The multicomponent blends exhibited significant increases in strain at break as compared to neat PLA and were subjected to a range of uniaxial strains (10–90%) at room temperature. These cold drawn materials exhibited nearly constant cross-sectional area and fine micro-cellular structures, as revealed by scanning electron microscopy. Distinct different voiding mechanisms observed for the PBE- and PP-containing blends were ascribed to the differences in the dispersed phase elastic moduli and deformability. The material density of cold drawn blends was reduced by up to 34% when compared to the precursor blends without a noticeable change in cross-sectional area. The novel low-density microcellular PLA blends demonstrated outstanding mechanical properties such as high strength, high modulus, substantial ductility, and a 14-fold increase in impact resistance as compared to PLA homopolymer.
Co-reporter:Saibom Park, Siyao He, Jianeng Wang, Andreas Stein, Christopher W. Macosko
Polymer 2016 Volume 104() pp:1-9
Publication Date(Web):8 November 2016
DOI:10.1016/j.polymer.2016.09.058
•We covalently attach alkyl chains and benzyl moieties to graphene oxide.•This FGO was solvent blended into three types of polyethylene: high density, linear low density, and oxidized PE matrices.•Simple thermal reduction of the FGO sheets dispersed in PE at 210 °C achieved a 106-fold reduction in electrical resistance, much greater than that of other unmodified graphene composites.•Moreover the tensile modulus of the low density PE was improved 12-fold and that of the high density PE 3-fold with 5% FGO.The properties of polymer nanocomposites depend strongly on how well nanoparticles are dispersed. However, the hydrophobic nature and low polarity of PE have made effective dispersion of nano-filler difficult without compatibilization. We have found improved dispersion of chemically functionalized graphene oxide (FGO) in PE. The hydroxyl and epoxide groups on graphene oxide (GO) are sites for grafting on functional groups like alkanes. We covalently attach alkyl chains and benzyl moieties to GO. This FGO was solvent blended into three types of polyethylene: high density, linear low density, and oxidized PE matrices. Visual observation of cast films and optical micrographs revealed that FGO was more homogeneously dispersed than unmodified GO. Simple thermal reduction of the FGO sheets dispersed in PE at 210 °C achieved a 106-fold reduction in electrical resistance, much greater than that of other unmodified graphene composites. Moreover the tensile modulus of the low density PE was improved 12-fold and that of the high density PE 3-fold with 5% FGO.
Co-reporter:Alexander M. Mannion, Frank S. Bates, and Christopher W. Macosko
Macromolecules 2016 Volume 49(Issue 12) pp:4587-4598
Publication Date(Web):June 16, 2016
DOI:10.1021/acs.macromol.6b00792
To improve the toughness and processability of poly(lactic acid) (PLA), a branched multiblock polymer was prepared from d,l-lactide and ε-decalactone. A hydroxy telechelic four-arm star poly(ε-decalactone)–poly(d,l-lactide) diblock was synthesized using sequential ring-opening transesterfication polymerization (ROTEP) and coupled using a substoichiometric amount of sebacoyl chloride to obtain a segmented multiblock with a comb-like architecture. Small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM) revealed that this branched multiblock was microphase separated but lacked long-range order. Unlike a linear multiblock of similar mass, the branched material demonstrated significant extensional hardening in the disordered state, suggesting much improved processability in polymer processing methods that require fast elongational flows. Additionally, the branched multiblock material exhibited remarkable tensile toughness. This simple synthetic approach allows for simultaneous control of mechanical and rheological properties using a single macromolecular architecture to address key practical issues with PLA.
Co-reporter:Sijia Huang, Lian Bai, Milana Trifkovic, Xiang Cheng, and Christopher W. Macosko
Macromolecules 2016 Volume 49(Issue 10) pp:3911-3918
Publication Date(Web):May 5, 2016
DOI:10.1021/acs.macromol.6b00212
Cocontinuous polymer blends have wide applications. They can form conductive plastics with improved mechanical properties. When one phase is extracted, they yield porous polymer sheets, which can be used as filters or membrane supports. However, the cocontinuous morphology is intrinsically unstable due to coarsening during static annealing. In this study, silica nanoparticles, ∼100 nm diameter, with different wetting properties were melt compounded in polyethylene/poly(ethylene oxide) blends. Calculated wetting coefficients of these particles match well with their phase contact angles and their locations in the blends. We demonstrated that a monolayer of particles jamming at interfaces can effectively suppress coarsening and stabilize the cocontinuous morphology. We also correlated the wettability of individual particles at interface to their coarsening suppression ability and found that the most hydrophobic silica nanoparticle is the most effective to arrest coarsening. Moreover, during annealing, we used the rheological dynamic time sweep, a facial but sensitive method, to relate the morphology change with particle dispersion on the interface. We further corroborated these measurements by scanning electron microscopy and confocal microscopy imaging.
Co-reporter:Zaifei Wang, Xiaotun Liu, Christopher W. Macosko, Frank S. Bates
Polymer 2016 Volume 101() pp:269-273
Publication Date(Web):28 September 2016
DOI:10.1016/j.polymer.2016.08.058
•A commercial water-extractable sulfopolyester (SP) was applied to melt blowing.•Nanofibers were fabricated from melt-blown immiscible polymer blends containing SP.•Water-extraction provides a green approach to producing melt-blown nanofibers.•A new route to prepare multilayer melt-blown nano-/micro-fiber composites.Nanofibers were prepared from water-extractable melt-blown immiscible polymer blends containing a commercial sulfopolyester (SP) as the sacrificial phase. Application of the water-dispersible SP eliminates issues associated with organic solvents, providing a facile, economic, and environment-friendly approach to high throughput fabrication of melt-blown nanofibers with an average diameter as small as 66 nm. Moreover, this approach offers a new route to prepare multilayer melt-blown nano-/micro-fiber composites. We demonstrate the fabrication of porous double-layer melt-blown PBT nano-/micro-fiber composites by tuning the collection time of the melt-blown SP/PBT blend fibers. Such materials are potentially useful for filtration media.
Co-reporter:Yong Tae Park;Yuqiang Qian;Clement Chan;Taewon Suh;Mehrdad Ghasemi Nejhad;Andreas Stein
Advanced Functional Materials 2015 Volume 25( Issue 4) pp:575-585
Publication Date(Web):
DOI:10.1002/adfm.201402553
The toughening effects of graphene and graphene-derived materials on thermosetting epoxies are investigated. Graphene materials with various structures and surface functional groups are incorporated into an epoxy resin by in situ polymerization. Graphene oxide (GO) and GO modified with amine-terminated poly(butadiene-acrylonitrile) (ATBN) are chosen to improve the dispersion of graphene nanosheets in epoxy and increase their interfacial adhesion. An impressive toughening effect is observed with less than 0.1 wt% graphene. A maximum in toughness at loadings as small as 0.02 wt% or 0.04 wt% is observed for all four types of graphene studied. An epoxy nanocomposite with ATBN-modified GO shows a 1.5-fold improvement in fracture toughness and a corresponding 2.4-fold improvement in fracture energy at 0.04 wt% of graphene loading. At such low loadings, these graphene-type materials become economically feasible components of nanocomposites. A microcrack mechanism is proposed based on microscopy of the fracture surfaces. Due to the stress concentration by graphene nanosheets, microcracks may be formed to absorb the fracture energy. However, above a certain graphene concentration, the coalescence of microcracks appears to facilitate crack propagation, lowering the fracture toughness. Crack deflection and pinning likely contribute to the slow increase in fracture toughness at higher loadings.
Co-reporter:Christopher M. Thurber, Yuewen Xu, Jason C. Myers, Timothy P. Lodge, and Christopher W. Macosko
ACS Macro Letters 2015 Volume 4(Issue 1) pp:30
Publication Date(Web):December 12, 2014
DOI:10.1021/mz500770y
We show catalyst localized at the interface can compatibilize polyethylene (PE) and polylactide (PLA) blends. Telechelic hydroxyl functional PE was synthesized by ring opening metathesis polymerization, which reacted with PLA in melt mixing (shown by adhesion and droplet size reduction). Lewis acid tin catalysts were examined as interfacial reaction promoters, with the goal of interfacial localization. Stannous octoate was shown to localize at the interface by transmission electron microscopy with energy dispersive X-ray spectroscopy and improved dispersion of PLA in PE as compared to uncatalyzed materials and a nonlocalized tin chloride dihydrate.
Co-reporter:Jing Han; Andrew R. Michel; Han Seung Lee; Stephen Kalscheuer; Adam Wohl; Thomas R. Hoye; Alon V. McCormick; Jayanth Panyam
Molecular Pharmaceutics 2015 Volume 12(Issue 12) pp:4329-4335
Publication Date(Web):October 27, 2015
DOI:10.1021/acs.molpharmaceut.5b00530
We have investigated particle size, interior structure, drug release kinetics, and anticancer efficacy of PEG-b-PLGA-based nanoparticles loaded with a series of paclitaxel (PTX)-silicate prodrugs [PTX-Si(OR)3]. Silicate derivatization enabled us to adjust the hydrophobicity and hydrolytic lability of the prodrugs by the choice of the alkyl group (R) in the silicate derivatives. The greater hydrophobicity of these prodrugs allows for the preparation of nanoparticles that are stable in aqueous dispersion even when loaded with up to ca. 75 wt % of the prodrug. The hydrolytic lability of silicates allows for facile conversion of prodrugs back to the parent drug, PTX. A suite of eight PTX-silicate prodrugs was investigated; nanoparticles were made by flash nanoprecipitation (FNP) using a confined impingement jet mixer with a dilution step (CIJ-D). The resulting nanoparticles were 80–150 nm in size with a loading level of 47–74 wt % (wt %) of a PTX-silicate, which corresponds to 36–59 effective wt % of free PTX. Cryogenic transmission electron microscopy images show that particles are typically spherical with a core–shell structure. Prodrug/drug release profiles were measured. Release tended to be slower for prodrugs having greater hydrophobicity and slower hydrolysis rate. Nanoparticles loaded with PTX-silicate prodrugs that hydrolyze most rapidly showed in vitro cytotoxicity similar to that of the parent PTX. Nanoparticles loaded with more labile silicates also tended to show greater in vivo efficacy.
Co-reporter:Lian Bai, John W. Fruehwirth, Xiang Cheng and Christopher W. Macosko
Soft Matter 2015 vol. 11(Issue 26) pp:5282-5293
Publication Date(Web):08 Jun 2015
DOI:10.1039/C5SM00994D
Bicontinuous, interfacially jammed, emulsion gels (bijels) are a novel class of materials composed of two immiscible phases with interpenetrating domains that are stabilized by a monolayer of colloidal particles at the interface. However, existing bijel systems so far all consist of at least one polar fluid, which is believed to be essential to induce electrostatic repulsion for stabilizing interfacial particles. It is not known whether two nonpolar fluids can form a bijel. Here, we experimentally achieve a bijel using styrene trimer and low molecular weight polybutene—two nonpolar fluids that are similar to polymer blends, which are important in technical applications. By combining laser scanning confocal microscopy, cryo-SEM and rheology measurement, we systematically investigate the dynamics and rheology of this nonpolar bijel. In contrast to previous studies on polar bijels, we observe the formation of localized regions of high particle concentration or “particle patches” on the interface which assemble during coarsening. We also provide the first quantitative relation between the morphology of a bijel, the interfacial particle coverage and the shear modulus during bijel coarsening. Moreover, we reveal a previously unnoticed increase in the elastic modulus of bijels that can be attributed to the rearrangement of interfacial particles at long time scales. In addition, we also found a hydrophobic particle framework that survives after the direct remixing of the nonpolar bijel. Our study provides important insights into the formation of bijels and is the first step to explore the missing link between polar bijels and particle-stabilized bicontinuous polymer blends.
Co-reporter:Yuewen Xu, Jesse Loi, Paula Delgado, Vasily Topolkaraev, Ryan J. McEneany, Christopher W. Macosko, and Marc A. Hillmyer
Industrial & Engineering Chemistry Research 2015 Volume 54(Issue 23) pp:6108-6114
Publication Date(Web):June 3, 2015
DOI:10.1021/acs.iecr.5b00882
Polylactide (PLA) was melt blended with either polypropylene (PP) or a polypropylene based elastomer (PBE, Vistamaxx) in an effort to improve its mechanical properties. An ethylene–glycidyl methacrylate–methyl acrylate terpolymer (PEGMMA, Lotader) was utilized as compatibilizer through coupling to the end groups of PLA. Graft copolymers formed enhanced the adhesion between PLA and polyolefin phases and lowered the interfacial tension. The morphological, mechanical, and rheological properties of the PLA/polyolefin compatibilized blends were investigated, and the blends exhibited substantial improvement in elongation at break and tensile toughness as compared to the corresponding binary blends. The remarkable efficacy of PEGMMA as a reactive compatibilizing agent allows the bridging of two immiscible but important classes of thermoplastics, polylactide and polypropylene, and the production of ductile PLA/PP blend materials.
Co-reporter:Milana Trifkovic, Aaron T. Hedegaard, Mehdi Sheikhzadeh, Sijia Huang, and Christopher W. Macosko
Macromolecules 2015 Volume 48(Issue 13) pp:4631-4644
Publication Date(Web):June 19, 2015
DOI:10.1021/acs.macromol.5b00354
Organomodified clays are known to be effective in polymer blend compatibilization if located preferentially at the domain interfaces, but little is known regarding the origin of their localization. In this study, we investigate the effect of organomodifier, clay loading, and shear environment on the compatibilization extent in nonreactive polyethylene (LDPE)/poly(ethylene oxide) (PEO) and reactive maleic anhydride functional polyethylene (PE-g-MA)/PEO polymer blends. We pose important questions: If clay is to compatibilize blends by interfacial localization, how does organomodifier affect its localization? How does an increase in clay loading affect the shape and elasticity of the interface? What is the shear intensity needed to overcome the equilibrium distribution of clays and delaminate it from the interface? We utilize laser scanning confocal microscopy and 3D image analysis to calculate characteristic phase size and gain unique insights into the connection between the clay loading and the interfacial curvature. Our experiments demonstrate that 1 wt % of interfacially localized clay is sufficient to suppress coarsening and greatly reduce phase domains. However, further increase of clay loading only saw a marginal reduction in phase size compared to 1 wt % clay loading. The interfacial curvature calculations showed that with increase in clay loadings beyond 1 wt % the shape of the interface does not change significantly; however, slight broadening of curvature distribution and increasing asymmetry are observed from 3D images. This can be attributed to the multiple layers of clay jammed at the interface at higher clay loadings. When reactive PE-g-MA was substituted for LDPE, graft copolymers were generated via in situ coupling at the interface. These copolymers combined with clay resulted in the smallest phase domains. In addition, we show that clay dispersion and localization were largely independent of shear intensity, which suggests that clay does not delaminate from the interface even in high shear environments.
Co-reporter:Katherine Margulis, Shlomo Magdassi, Han Seung Lee, Christopher W. Macosko
Journal of Colloid and Interface Science 2014 Volume 434() pp:65-70
Publication Date(Web):15 November 2014
DOI:10.1016/j.jcis.2014.07.040
•A new method for production of organic nanoparticles is demonstrated for curcumin.•The method is based on flash nanoprecipitation from partially water-soluble emulsions.•A simple hand-operated mixer is employed for flash nanoprecipitation process.•Dry nanometric powders obtained by spray drying are easily dispersible in water.•The resultant particles are 40 nm in diameter and contain above 20 wt% active substance.Nanometric particles of a model hydrophobic substance curcumin were prepared by a novel method, namely, flash nanoprecipitation from a coarse oil-in-water emulsion. The method employs turbulent co-mixing of water with curcumin-loaded emulsion using manually-operated confined impingement jets mixer. A clear and stable dispersion of nanoparticles was formed in this process, and could be converted to dry, easily water-dispersible powder by spray drying. The mean size of the particles was about 40 nm by DLS, confirmed by Cryo-TEM. The obtained particles contained 20.4 wt% curcumin, X-ray analysis showed it was amorphous. The significant advantages of the studied process are its feasibility, speed and low cost. It does not require any special high-energy input equipment to reduce the droplet size of the initial emulsion as required by the vast majority of other methods, and relies on rapid turbulent mixing and on flow-induced shear stress formed in the simple, manually-operated mixer. Control experiments clearly indicate that employing emulsion, instead of a plain solution and flash nanoprecipitation instead of a simple antisolvent precipitation are advantageous in terms of particle size and stability.Figure optionsDownload full-size imageDownload high-quality image (187 K)Download as PowerPoint slide
Co-reporter:Shigeru Aoyama, Yong Tae Park, Toshiaki Ougizawa, Christopher W. Macosko
Polymer 2014 Volume 55(Issue 8) pp:2077-2085
Publication Date(Web):10 April 2014
DOI:10.1016/j.polymer.2014.02.055
Poly(ethylene terephthalate) (PET)-based nanocomposites with graphene or multi-wall carbon nanotubes (MWCNT) were prepared by melt mixing. Aspect ratio, Af, and interparticle distance, λ, of graphene in the nanocomposites were obtained from melt rheology and transmission electron microscopy respectively. λ of PET/graphene nanocomposites was much smaller than λ in PET/MWCNT. For PET/graphene with highest Af, λ became <1 μm at more than 0.5 wt% graphene. Non-isothermal crystallization behavior from the melt was investigated by differential scanning calorimetry. The crystallization temperatures suggest that the nucleation effect of graphene was stronger than that of MWCNT. The half crystallization time of PET/graphene became longer than PET/MWCNT with increasing graphene loading, suggesting that confinement by graphene suppressed the crystal growth rate. XRD analysis indicated that smaller crystals formed in PET/graphene than in PET/MWCNT. From Raman spectroscopy, the π–π interaction between PET and graphene was stronger than that between PET and MWCNT. This stronger interaction in PET/graphene appears to result in formation of crystals with higher perfection.
Co-reporter:Ken-Hsuan Liao, Shingo Kobayashi, Hyunwoo Kim, Ahmed A. Abdala, and Christopher W. Macosko
Macromolecules 2014 Volume 47(Issue 21) pp:7674-7676
Publication Date(Web):October 28, 2014
DOI:10.1021/ma501709g
Co-reporter:Ken-Hsuan Liao, Shigeru Aoyama, Ahmed A. Abdala, and Christopher Macosko
Macromolecules 2014 Volume 47(Issue 23) pp:8311-8319
Publication Date(Web):November 24, 2014
DOI:10.1021/ma501799z
The effect of the addition of graphene on the glass transition temperature (Tg) of polymers was investigated, first with poly(methyl methacrylate) and then with an extensive literature review. Isotactic (i-PMMA) and atactic PMMA (a-PMMA) were blended with pristine graphene (PG) and thermally reduced graphene (TRG). A Tg increase was found for a-PMMA nanocomposites made via in situ polymerization with TRG but not when a-PMMA was solvent blended with TRG. However, a Tg increase was found for TRG solvent blended into i-PMMA and a smaller increase for PG with i-PMMA. Nearly all the increase occurred at the lowest loading, 0.25 wt %, with little change at increased graphene concentration. Tg increases due to interfacial interactions between matrix polymers and fillers. Physical blending such as solvent processes cannot provide enough interaction at the interfaces, whereas chemical blending processes such as in situ polymerization can yield strong covalent bonds. However, i-PMMA molecules can align on graphene sheets at the interface, creating more interaction between i-PMMA and graphene than a-PMMA. Also, the Tg of i-PMMA is 60 °C lower than a-PMMA, meaning that hydrogen bonds are stronger at the lower temperature. The Tg increase of TRG/i-PMMA is higher than that of PG/i-PMMA due to more oxygen functionalities on TRG than on PG to act as interfacial interaction sites. A broad literature survey agrees with our PMMA results. We found no changes in Tg for graphene/polymer nanocomposites synthesized via physical blending processes such as solvent or melt blending, except for blending with strongly polar polymers. In contrast, chemical blending processes such as in situ polymerization or chemically modified fillers yielded significant Tg increases in graphene/polymer nanocomposites.
Co-reporter:Yong Tae Park, Yuqiang Qian, Chris I. Lindsay, Conny Nijs, Rafael E. Camargo, Andreas Stein, and Christopher W. Macosko
ACS Applied Materials & Interfaces 2013 Volume 5(Issue 8) pp:3054
Publication Date(Web):March 18, 2013
DOI:10.1021/am303244j
The largest use of polyurethane (PU) is as closed cell rigid foams for thermal insulation. One problem is loss of blowing gases, which leads to slow increase in thermal conductivity. PU composites with plate-like nanofillers create a diffusion barrier, reducing gas transport and slowing insulation aging. In this research, a new in situ intercalative polymerization is described to disperse vermiculite (VMT) in PU. When VMT was modified by cation exchange with long-chain quaternary ammonium, the dispersion in methylene diphenyl diisocyanate (MDI) was significantly improved. Dispersion of clay in MDI was further improved by combining high intensity dispersive mixing with a polyol-clay preblend (master-batch). The VMT dispersibility was characterized using rheology, microscopy, and X-ray scattering/diffraction. With the method of polyol-assisted VMT dispersion, electron microscopy revealed extensive intercalation and exfoliation of clay particles. In contrast, simple mixing of organoclay in MDI resulted in macroscopic localization and poor distribution of clay particles in PU. The final nanocomposites prepared by the master-batch method showed enhancement of mechanical properties (85% increase in elastic modulus) and reduction in permeability to CO2, as much as 40%, at a low clay concentration of 3.3 wt %.Keywords: gas barrier; organoclay; polymer−clay nanocomposite; polyurethane; vermiculite;
Co-reporter:Feng Zuo, Dawud H. Tan, Zaifei Wang, Soondeuk Jeung, Christopher W. Macosko, and Frank S. Bates
ACS Macro Letters 2013 Volume 2(Issue 4) pp:301
Publication Date(Web):March 26, 2013
DOI:10.1021/mz400053n
Nanofibers were generated by melt blowing three sets of polymer blends, each comprised of pairs of immiscible components. Blends containing minority phases (25% by volume) of poly(ethylene-co-chlorotrifluoroethylene) (PECTFE) in poly(butylene terephthalate) (PBT), PECTFE in poly(styrene) (PS), and PBT in PS were dispersed as droplets in a continuous majority phase and melt blown into long (>100 μm) fibers with average diameters of several micrometers. Electron microscopy experiments revealed that melt blowing transformed the initial spherical dispersions into a nanofiber-in-fiber morphology. Macroscopic mats of nonwoven PBT and PECTFE nanofibers, with average diameters as small as 70 nm, were isolated by selectively removing the majority phase with a solvent. This method provides a potentially inexpensive, high throughput, one-step route to scalable quantities of polymeric nanofibers.
Co-reporter:Kevin M. Pustulka, Adam R. Wohl, Han Seung Lee, Andrew R. Michel, Jing Han, Thomas R. Hoye, Alon V. McCormick, Jayanth Panyam, and Christopher W. Macosko
Molecular Pharmaceutics 2013 Volume 10(Issue 11) pp:4367-4377
Publication Date(Web):September 20, 2013
DOI:10.1021/mp400337f
Flash nanoprecipitation (FNP) is a process that, through rapid mixing, stabilizes an insoluble low molecular weight compound in a nanosized, polymer-stabilized delivery vehicle. The polymeric components are typically amphiphilic diblock copolymers (BCPs). In order to fully exploit the potential of FNP, factors affecting particle structure, size, and stability must be understood. Here we show that polymer type, hydrophobicity and crystallinity of the small molecule, and small molecule loading levels all affect particle size and stability. Of the four block copolymers (BCP) that we have studied here, poly(ethylene glycol)-b-poly(lactic-co-glycolic acid) (PEG-b-PLGA) was most suitable for potential drug delivery applications due to its ability to give rise to stable nanoparticles, its biocompatibility, and its degradability. We found little difference in particle size when using PLGA block sizes over the range of 5 to 15 kDa. The choice of hydrophobic small molecule was important, as molecules with a calculated water–octanol partition coefficient (clogP) below 6 gave rise to particles that were unstable and underwent rapid Ostwald ripening. Studies probing the internal structure of nanoparticles were also performed. Analysis of differential scanning calorimetry (DSC), cryogenic transmission electron microscopy (cryo-TEM), and 1H NMR experiments support a three-layer core–shell–corona nanoparticle structure.Keywords: core−shell particles; drug delivery; flash nanoprecipitation; insoluble drugs; paclitaxel;
Co-reporter:Ken-Hsuan Liao, Yong Tae Park, Ahmed Abdala, Christopher Macosko
Polymer 2013 Volume 54(Issue 17) pp:4555-4559
Publication Date(Web):2 August 2013
DOI:10.1016/j.polymer.2013.06.032
Aqueous reduction of graphene oxide is a low energy and hazardous-chemical free method to produce graphene. In this article, we report the first polymer nanocomposites with aqueous reduced graphene (ARG). Dispersion of ARG in polymer can be challenging because of the aggregation and stacking of single sheets during the removal of water. A novel co-solvent process to blend ARG into thermoplastic polyurethane (TPU) avoids drying ARG by adding an organic solvent before water is completely removed from the aqueous reduction mixture. The dispersion of ARG in TPU was significantly improved using the co-solvent process compared to conventional solvent blending as demonstrated by the mechanical and electrical properties of ARG/TPU composites. Moreover, properties of the co-solvent blended ARG composite are similar to those of the composites of thermally reduced graphene (TRG), which are the best reported to date. We believe that using solvent exchange to avoid aggregation during drying is a general strategy applicable to other nanocomposite preparations.
Co-reporter:Jing Han;Zhengxi Zhu;Haitao Qian;Adam R. Wohl;Charles J. Beaman;Thomas R. Hoye
Journal of Pharmaceutical Sciences 2012 Volume 101( Issue 10) pp:4018-4023
Publication Date(Web):
DOI:10.1002/jps.23259
Abstract
Johnson and Prud′homme (2003. AICHE J 49:2264–2282) introduced the confined impingement jets (CIJ) mixer to prepare nanoparticles loaded with hydrophobic compounds (e.g., drugs, inks, fragrances, or pheromones) via flash nanoprecipitation (FNP). We have modified the original CIJ design to allow hand operation, eliminating the need for a syringe pump, and we added a second antisolvent dilution stage. Impingement mixing requires equal flow momentum from two opposing jets, one containing the drug in organic solvent and the other containing an antisolvent, typically water. The subsequent dilution step in the new design allows rapid quenching with high antisolvent concentration that enhances nanoparticle stability. This new CIJ with dilution (CIJ-D) mixer is a simple, cheap, and efficient device to produce nanoparticles. We have made 55 nm diameter β-carotene nanoparticles using the CIJ-D mixer. They are stable and reproducible in terms of particle size and distribution. We have also compared the performance of our CIJ-D mixer with the vortex mixer, which can operate at unequal flow rates (Liu et al., 2008. Chem Eng Sci 63:2829–2842), to make β-carotene-containing particles over a series of turbulent conditions. On the basis of dynamic light scattering measurements, the new CIJ-D mixer produces stable particles of a size similar to the vortex mixer. Our CIJ-D design requires less volume and provides an easily operated and inexpensive tool to produce nanoparticles via FNP and to evaluate new nanoparticle formulation. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:4018–4023, 2012
Co-reporter:Jie Song;Anne Bringuier;Shingo Kobayashi;Adam M Baker;Christopher W Macosko
Polymer Journal 2012 44(9) pp:939-945
Publication Date(Web):2012-03-28
DOI:10.1038/pj.2012.25
To understand the effect of processing and co-monomer content on interfacial adhesion, we quantified adhesion levels of bilayers of a polyethylene (PE) with various polypropylenes (PPs) prepared using bilayer co-extrusion and lamination processes. We tested adhesion between a medium-density PE (MDPE) with different types of PPs, including impact-modified PP (with various amount of ethylene), isotactic PP and ethylene–propylene random copolymers. Increasing the concentration of ethylene or ethylene–propylene rubber gave rise to increased adhesion. The impact-modified PP with 20 wt% ethylene content exhibited adhesion with MDPE almost two orders of magnitude higher compared with other PPs. Although lamination and co-extrusion processes showed good agreement in these trends with ethylene content, the operation parameters are critical for adhesion control. For lamination, ice-water cooling generated a stronger adhesion than that with air cooling. Faster cooling rates in co-extrusion also gave rise to stronger adhesion. Increasing draw down ratio and varying flow rate to put the interface near the wall resulted in stronger adhesion. Fast quenching rate and increased crystallinity induced by drawing down are believed to be the causes. Both atomic force microscopy and transmission electron microscopic images exhibited roughened interfaces for samples with strong adhesion.
Co-reporter:Ken-Hsuan Liao, Yuqiang Qian, Christopher W. Macosko
Polymer 2012 Volume 53(Issue 17) pp:3756-3761
Publication Date(Web):2 August 2012
DOI:10.1016/j.polymer.2012.06.020
Polyurethane acrylate (PUA) are widely used as coating for automobile industry. Making these coatings electrically conductive would open up new applications. Using thermally reduced graphene (TRG) and in-situ polymerization we have created PUA nanocomposites with an ultralow percolation concentration of 0.15 wt% (0.07 vol%) graphene. Urethane-acrylate oligomer (UAO) was synthesized and diluted by tripropyleneglycol diacrylate (TPGDA) to form flowable UAO/TPGDA mixture (UA). TRG was solvent-blended in UA to form uncured TRG/UA liquids and were polymerized by free radical polymerization with azobisisobutyronitrile (AIBN) initiator. Percolation concentrations of polymerized TRG/PUA nanocomposites occurred at 0.15 wt% (0.07 vol%), as determined by surface resistance measurements, bulk electrical conductivity, and modulus. TEM images revealed a homogeneous dispersion of TRG in PUA. Differential scanning calorimetry (DSC) was used to monitor the polymerization of TRG/UA uncured liquids and thermal properties of polymerized TRG/PUA nanocomposites. Polymerization heat, glass transition temperature, and polymerization temperature are independent of TRG loading, though polymerization temperature is ∼10 °C lower in the absence of TRG.Graphical abstract
Co-reporter:Jie Song, Christopher M. Thurber, Shingo Kobayashi, Adam M. Baker, Christopher W. Macosko, H. Craig Silvis
Polymer 2012 Volume 53(Issue 16) pp:3636-3641
Publication Date(Web):19 July 2012
DOI:10.1016/j.polymer.2012.05.057
Functionalized poly(propylene-co-ethylene) (PPE) made via reactive extrusion dramatically improved the performance of their blends with poly(methyl methacrylate) (PMMA). Adhesion, compatibility, modulus, hardness and scratch resistance were all increased for blends with functional PPEs compared to non-modified PPE, greatly expanding the applications of polyolefins. Three types of functional PPEs including maleic anhydride grafted PPE (PPE-MA), hydroxyl group grafted PPE (PPE-OH) and secondary amine group grafted PPE (PPE-NHR) were melt blended with PMMA at different compositions and with PMMA of different molecular weights. Compatibility of each functional PPE with PMMA was compared by investigating the binary blends using mechanical (nano-indentation, nano-scratch and tensile tests), morphological (scanning electron microscopy with image analysis, particle size analysis) and adhesion tests. Compatibility of functional PPEs with PMMA is confirmed consistently from various tests and ranked in a decreasing order as follows: PPE-NHR > PPE-OH > PPE-MA > PPE. We also drastically improved the compatibility and adhesion between PPE and PMMA by blending a small amount of PMMA grafted PPE copolymer.
Co-reporter:Yuqiang Qian, Wenhao Liu, Yong Tae Park, Chris I. Lindsay, Rafael Camargo, Christopher W. Macosko, Andreas Stein
Polymer 2012 Volume 53(Issue 22) pp:5060-5068
Publication Date(Web):12 October 2012
DOI:10.1016/j.polymer.2012.09.008
In situ intercalative polymerization is an environmentally-friendly process to produce polymer-clay nanocomposites with good clay dispersion. In this work, quaternary ammonium salts with tertiary amine groups were synthesized to modify clay as catalytically active modifiers for polyurethanes. Polyol dispersions with the catalyst-modified vermiculites were prepared by ultrasonication and examined by X-ray scattering and rheology. In the polyurethane elastomers synthesized from the above dispersions in a solvent-free process, X-ray scattering showed that the clay was highly intercalated/exfoliated without noticeable peaks for d < 9 nm, and TEM images revealed that the local dispersion of clay sheets was affected by the structure of the modifier. Addition of the modified clay to the polyurethane elastomers had only a small effect on the phase separation between hard and soft segments as deduced from DSC, FT-IR and DMA results. Thermo-mechanical and barrier properties of the composites were evaluated, and with one modifier, the nanocomposites showed a 390% increase in tensile modulus at 25 °C and a 40% reduction in CO2 permeability at a loading of 5.3 wt% of catalyst-modified clay.Graphical abstract
Co-reporter:Ken-Hsuan Liao, Yu-Shen Lin, Christopher W. Macosko, and Christy L. Haynes
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 7) pp:2607
Publication Date(Web):June 8, 2011
DOI:10.1021/am200428v
Two-dimensional carbon-based nanomaterials, including graphene oxide and graphene, are potential candidates for biomedical applications such as sensors, cell labeling, bacterial inhibition, and drug delivery. Herein, we explore the biocompatibility of graphene-related materials with controlled physical and chemical properties. The size and extent of exfoliation of graphene oxide sheets was varied by sonication intensity and time. Graphene sheets were obtained from graphene oxide by a simple (hydrazine-free) hydrothermal route. The particle size, morphology, exfoliation extent, oxygen content, and surface charge of graphene oxide and graphene were characterized by wide-angle powder X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, dynamic light scattering, and zeta-potential. One method of toxicity assessment was based on measurement of the efflux of hemoglobin from suspended red blood cells. At the smallest size, graphene oxide showed the greatest hemolytic activity, whereas aggregated graphene sheets exhibited the lowest hemolytic activity. Coating graphene oxide with chitosan nearly eliminated hemolytic activity. Together, these results demonstrate that particle size, particulate state, and oxygen content/surface charge of graphene have a strong impact on biological/toxicological responses to red blood cells. In addition, the cytotoxicity of graphene oxide and graphene sheets was investigated by measuring mitochondrial activity in adherent human skin fibroblasts using two assays. The methylthiazolyldiphenyl-tetrazolium bromide (MTT) assay, a typical nanotoxicity assay, fails to predict the toxicity of graphene oxide and graphene toxicity because of the spontaneous reduction of MTT by graphene and graphene oxide, resulting in a false positive signal. However, appropriate alternate assessments, using the water-soluble tetrazolium salt (WST-8), trypan blue exclusion, and reactive oxygen species assay reveal that the compacted graphene sheets are more damaging to mammalian fibroblasts than the less densely packed graphene oxide. Clearly, the toxicity of graphene and graphene oxide depends on the exposure environment (i.e., whether or not aggregation occurs) and mode of interaction with cells (i.e., suspension versus adherent cell types).Keywords: aggregation; cytotoxicity; graphene; hemolysis; viability assay;
Co-reporter:Yuqiang Qian, Chris I. Lindsay, Chris Macosko, and Andreas Stein
ACS Applied Materials & Interfaces 2011 Volume 3(Issue 9) pp:3709
Publication Date(Web):August 19, 2011
DOI:10.1021/am2008954
Natural vermiculite was modified by cation exchange with long-chain quaternary alkylammonium salts and then dispersed in polyether-based polyols with different structures and ethylene oxide/propylene oxide ratios. The dispersions were evaluated by X-ray scattering and rheology. In all polyol dispersions tested, polyols were intercalated into the vermiculite interlayers. Also, significant shear thinning behavior was observed. A large interlayer spacing of ∼90 Å was achieved in one polyol suitable for polyurethane elastomer synthesis. In polyurethane made with this polyol, clay platelets were extensively intercalated or exfoliated. The composites showed a >270% increase in tensile modulus, >60% increase in tensile strength, and a 30% reduction in N2 permeability with a loading of 5.3 wt % clay in polyurethane. Differential scanning calorimetry and dynamic mechanical analysis revealed that the nanoclay interacts with the polyurethane hard segments.Keywords: barrier properties; elastomer; organoclay; polymer−clay nanocomposites; polyurethane; vermiculite;
Co-reporter:Shingo Kobayashi, Jie Song, H. Craig Silvis, Christopher W. Macosko, and Marc A. Hillmyer
Industrial & Engineering Chemistry Research 2011 Volume 50(Issue 6) pp:3274-3279
Publication Date(Web):February 21, 2011
DOI:10.1021/ie102005q
Primary and secondary amino-functionalized polyethylenes were synthesized from commercially available maleic anhydride-modified polyethylene by reaction with mono-tert-butoxycarbonyl-protected diamines, N-(tert-butoxycarbonyl)-1,6-diaminohexane (tBocHMDA), and N-(tert-butoxycarbonyl)-N-ethyl-1,6-diaminohexane (tBocEtHMDA) followed by deprotection with trifluoroacetic acid. The structures of amino-functionalized polyethylenes were characterized by NMR and IR spectroscopies, and the data compared favorably to that of the corresponding model compounds. The amino-functionalized polymers showed significantly improved adhesive strength toward thermoplastic polyurethanes as compared to the parent maleic anhydride-modified polyethylene.
Co-reporter:Jie Song, Ashish Batra, Jose M. Rego, Christopher W. Macosko
Progress in Organic Coatings 2011 Volume 72(Issue 3) pp:492-497
Publication Date(Web):November 2011
DOI:10.1016/j.porgcoat.2011.06.008
Polyolefins have low free surface energy that prevents good wettability of adhesives or paint emulsions to their surface. This work shows that adhesion of olefin block copolymers (OBC) to a polyurethane-based paint can be significantly improved by blending thermoplastic polyurethane (TPU) into OBC. Furthermore, blend morphologies near the paint/polymer interface, and surface compositions of injection molded plaques, were characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared spectroscopy with attenuated total reflectance (FTIR-ATR) in order to explore the underlying mechanism of paint adhesion to TPU/OBC blends. It was found that for 35 wt% and 25 wt% TPU loading, the top paint layer is well-attached at the interface, whereas for 15 wt% loading, there was incomplete wetting of the paint, and a gap between the polymer substrate and paint was apparent. XPS and SEM gave consistent results demonstrating that outermost surface composition of TPU in these blends is slightly higher than in the bulk. It is speculated here that, during painting and the subsequent drying step, polyurethane chains from the paint diffuse into the blend substrate and entangle with TPU in the blend. The entanglement between paint and substrate generates a physical link that provides adhesion.Highlights• Adhesion of polyolefin to paint is significantly improved by blending polyurethane. • Outermost surface of injection molded blends is determined to have more TPU. • Composition of blends at 5 μm below surface is determined to be the same as bulk. • SEM and AFM gave evidence on inter-diffusion between paint and substrate. • Polymer inter-diffusion is proposed as paint adhesion mechanism.
Co-reporter:Hyunwoo Kim, Shingo Kobayashi, Mohd A. AbdurRahim, Minglun J. Zhang, Albina Khusainova, Marc A. Hillmyer, Ahmed A. Abdala, Christopher W. Macosko
Polymer 2011 Volume 52(Issue 8) pp:1837-1846
Publication Date(Web):5 April 2011
DOI:10.1016/j.polymer.2011.02.017
Since its recent successful isolation, graphene has attracted an enormous amount of scientific interest due to its exceptional physical properties. Graphene incorporation can improve electrical and mechanical properties of polymers including polyethylene (PE). However, the hydrophobic nature and low polarity of PE have made effective dispersion of nano-fillers difficult without compatibilization. Graphene was derived from graphite oxide (GO) via rapid thermal exfoliation and reduction. This thermally reduced graphene oxide (TRG) was blended via melt and solvent blending with linear low density PE (LLDPE) and its functionalized analogs (amine, nitrile and isocyanate) produced using a ring-opening metathesis polymerization (ROMP) strategy. TRG was well exfoliated in functionalized LLDPE while phase separated morphology was observed in the un-modified LLDPE. Transmission electron micrographs showed that solvent based blending more effectively dispersed these exfoliated carbon sheets than did melt compounding. Tensile modulus was higher for composites with functionalized polyethylenes when solvent blending was used. However, at less than 3 wt.% of TRG, electrical conductivity of the un-modified LLDPE was higher than that of the functionalized ones. This may be due to phase segregation between graphene and PE, and electrical percolation within the continuous filler-rich phase.
Co-reporter:Ken-Hsuan Liao, Anudha Mittal, Shameek Bose, Christopher Leighton, K. Andre Mkhoyan, and Christopher W. Macosko
ACS Nano 2011 Volume 5(Issue 2) pp:1253
Publication Date(Web):January 27, 2011
DOI:10.1021/nn1028967
We report a new, simple, hydrazine-free, high-yield method for producing single-layer graphene sheets. Graphene sheets were formed from graphite oxide by reduction with simple deionized water at 95 °C under atmospheric pressure. Over 65% of the sheets are single graphene layers; the average sheet diameter is 300 nm. We speculate that dehydration of graphene oxide is the main mechanism for oxygen reduction and transformation of C−C bonds from sp3 to sp2. The reduction appears to occur in large uniform interconnected oxygen-free patches so that despite the presence of residual oxygen the sp2 carbon bonds formed on the sheets are sufficient to provide electronic properties comparable to reduced graphene sheets obtained using other methods.Keywords: aqueous route; dehydration; graphene; graphene oxide; oxygen reduction
Co-reporter:Suqin Tan, Tim Abraham, Don Ference, Christopher W. Macosko
Polymer 2011 Volume 52(Issue 13) pp:2840-2846
Publication Date(Web):8 June 2011
DOI:10.1016/j.polymer.2011.04.040
Polyurethane (PU) rigid foams were synthesized by substituting a polypropylene-based polyol with soybean oil-based polyol (SBOP). All the soy-based foams maintained a regular cell structure and had even smaller average cell size than the control foams. The density of soy-based foams was within 5% of the controls, except that the density of foams from 100% SBOP was 17% higher. Soy-based foams also had comparable initial thermal conductivity (k value) and closed cell content, higher Tg and compressive strength. However, while foams from 50% SBOP showed similar increase in k value to the 0% SBOP foams, under accelerated aging conditions, the 100% SBOP foams aged faster. Gas permeation tests performed on PU thin films showed higher N2 permeation for PU thin films made from SBOP which is believed to be the cause of accelerated thermal aging.
Co-reporter:Hyunwoo Kim, Yutaka Miura and Christopher W. Macosko
Chemistry of Materials 2010 Volume 22(Issue 11) pp:3441
Publication Date(Web):May 17, 2010
DOI:10.1021/cm100477v
Recently developed strategies for isolating single-layer carbon sheets from graphite have enabled production of electrically conductive, mechanically robust polymer nanocomposites with enhanced gas barrier performance at extremely low loading. In this article, we present processing, morphology, and properties of thermoplastic polyurethane (TPU) reinforced with exfoliated graphite. For the first time, we compare carbon sheets exfoliated from graphite oxide (GO) via two different processes: chemical modification (isocyanate treated GO, iGO) and thermal exfoliation (thermally reduced GO, TRG), and three different methods of dispersion: solvent blending, in situ polymerization, and melt compounding. Incorporation of as low as 0.5 wt % of TRG produced electrically conductive TPU. Up to a 10-fold increase in tensile stiffness and 90% decrease in nitrogen permeation of TPU were observed with only 3 wt % iGO, implying a high aspect ratio of exfoliated platelets. Real- and reciprocal-space morphological characterization indicated that solvent-based blending techniques more effectively distribute thin exfoliated sheets in the polymer matrix than melt processing. This observation is in good qualitative agreement with the dispersion level inferred from solid property enhancements. Although also processed in solvents, property increase via in situ polymerization was not as pronounced because of reduced hydrogen bonding in the TPU produced.
Co-reporter:Carlos R. López-Barrón and Christopher W. Macosko
Soft Matter 2010 vol. 6(Issue 12) pp:2637-2647
Publication Date(Web):22 Apr 2010
DOI:10.1039/B926191E
The coarsening of fluorescently labeled polystyrene/ styrene-ran-acrylonitrile copolymer symmetric blends with cocontinuous morphologies was studied with 3D imaging. Blends with three different interfacial tensions were analyzed. Two regimes of coarsening were observed: a linear growth of the characteristic size followed by a gradual decrease of the rate of coarsening. Only the linear regime was explained by the classical analysis of phase separating systems by Siggia (Phys. Rev. A, 1979, 20, 595). Here, we propose a new model which considers both the characteristic size and the interfacial curvature. This model is a generalization of Siggia's analysis, after including the contribution of the local curvature on the capillary pressure within the interconnected domains. Our capability to compute curvature data from 3D images of the blend microstructure allowed us to test our model. Additionally, a general expression for the coarsening rate proposed by Scholten et al. (E. Scholten, L. M. C. Sagis and E. van der Linden, Macromolecules, 2005, 38, 3515) was, for the first time, assessed here. Both early and late stages of coarsening were predicted with the new model, while Scholten et al. and Siggia's expressions are able to adequately describe only one stage. A crossover between the two regimes of coarsening took place at a single value of capillary number (Ca ∼ 0.003) for all three blends, as predicted by our new expression.
Co-reporter:Zhengxi Zhu;Katrin Margulis-Goshen;Shlomo Magdassi;Yeshayahu Talmon
Journal of Pharmaceutical Sciences 2010 Volume 99( Issue 10) pp:4295-4306
Publication Date(Web):
DOI:10.1002/jps.22090
Abstract
Polyelectrolyte protected β-carotene nanoparticles (nanosuspensions) with average diameter of <100 nm were achieved by turbulent mixing and flash nanoprecipitation (FNP). Three types of multi-amine functional polyelectrolytes, ε-polylysine (ε-PL), poly(ethylene imine) (PEI), and chitosan, were investigated to electrosterically protect the nanoparticles. Particle size and distribution were measured by dynamic light scattering (DLS); particles were imaged via scanning electron microscopy (SEM) and cryogenic transmission electron microscopy (cryo-TEM). Low pH and high polyelectrolyte molecular weight gave the smallest and most stable particles. High drug loading capacity, >80 wt%, was achieved by using either PEI or chitosan. X-ray diffraction (XRD) patterns showed that β-carotene nanoparticles were amorphous. These findings open the way for utilization of FNP for preparation of nanoparticles with enhanced bioavailability for highly water insoluble drugs. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:4295–4306, 2010
Co-reporter:Hyunwoo Kim, Ahmed A. Abdala and Christopher W. Macosko
Macromolecules 2010 Volume 43(Issue 16) pp:6515-6530
Publication Date(Web):July 23, 2010
DOI:10.1021/ma100572e
Graphene has emerged as a subject of enormous scientific interest due to its exceptional electron transport, mechanical properties, and high surface area. When incorporated appropriately, these atomically thin carbon sheets can significantly improve physical properties of host polymers at extremely small loading. We first review production routes to exfoliated graphite with an emphasis on top-down strategies starting from graphite oxide, including advantages and disadvantages of each method. Then solvent- and melt-based strategies to disperse chemically or thermally reduced graphene oxide in polymers are discussed. Analytical techniques for characterizing particle dimensions, surface characteristics, and dispersion in matrix polymers are also introduced. We summarize electrical, thermal, mechanical, and gas barrier properties of the graphene/polymer nanocomposites. We conclude this review listing current challenges associated with processing and scalability of graphene composites and future perspectives for this new class of nanocomposites.
Co-reporter:Jianbin Zhang, Shengxiang Ji, Jie Song, Timothy P. Lodge, and Christopher W. Macosko
Macromolecules 2010 Volume 43(Issue 18) pp:7617-7624
Publication Date(Web):September 1, 2010
DOI:10.1021/ma100889p
Reactive coupling of functional polymer chains has been reported to be 3 orders of magnitude slower at static interfaces than under mixing conditions, and the reaction rates under mixing are close to the rates measured in homogeneous melts [Jeon et al. Prog. Polym. Sci. 2005, 30, 939]. However, due to the complexity of interfacial area generation during mixing, it was difficult to isolate the effects of flow on reaction kinetics. In this paper, a reactive multilayer system was created to explore this issue. A 640-layer polystyrene (PS)/poly(methyl methacrylate) (PMMA) sample was fabricated with a multilayer coextruder. Each component contained 10 wt % functional polymer, an amine-terminal PS (PS-NH2), and an anthracence-labeled anhydride-terminal PMMA (PMMA-anh-anth), respectively. Coupling reactions between PS-NH2/PMMA-anh-anth occurred during extrusion. The reaction conversion was measured with size exclusion chromatography, and interfacial morphology was monitored with both scanning and transmission electron microscopy. It was found that a significant amount of PS-b-PMMA copolymer formed during coextrusion, such that the interfaces of the extrudate were almost completely saturated with the block copolymers formed in situ. The coupling reaction of PS-NH2/PMMA-anh-anth under coextrusion was as rapid as that under mixing and was up to 1000 times faster than that under quiescent annealing. Subsequent steady shear of the multilayer samples further increased the reaction conversion significantly but destroyed the layer structure. Micelles and swollen micelles were formed under shear. Dynamic shear did not promote any further reaction due to the already high interfacial coverage for the extrudate. In contrast, for a simple laminated bilayer sample with nearly zero interfacial coverage, reactive coupling was promoted significantly by dynamic shear as evidenced by interfacial roughening. We speculate that the high surface energy of the functional chain ends causes them to be depleted near the interface, leading to very slow coupling under quiescent conditions. Moreover, the diffusion of polymer chains very close to the surface has been reported to be much slower than in bulk. Under coextrusion or mixing, external flow increased the functional group concentration in the interfaces, restoring reaction rates to the level expected under homogeneous conditions. The uniformity of block copolymer formation across the coextruded sample argues that extensional deformation is more important than shear in accelerating coupling.
Co-reporter:Joel R. Bell, Kwanho Chang, Carlos R. López-Barrón, Christopher W. Macosko and David C. Morse
Macromolecules 2010 Volume 43(Issue 11) pp:5024-5032
Publication Date(Web):May 5, 2010
DOI:10.1021/ma902805x
Cocontinuous morphologies of polymer blends are thermodynamically unstable: they will coarsen when held above their glass or melting transition temperature. We have found that properly chosen diblock copolymers (bcp) can arrest coarsening during quiescent annealing. The effects of bcp on the cocontinuous morphologies of polystyrene (PS)/polyethylene (PE), PS/poly(methyl methacrylate) (PMMA) and PS/styrene-ran-acrylonitrile copolymer (SAN) blends were studied using scanning electron microscopy (SEM) and laser scanning confocal microscopy (LSCM) with image analysis. Bcp effectiveness was dependent on copolymer molecular weight, concentration, and asymmetry. Our interpretation emphasizes the role of bcp micelle creation and destruction as potential bottlenecks in the kinetics of interfacial adsorption of copolymer during mixing and of interfacial desorption during coarsening. In cases where adsorption and desorption appear to be facile, our results for the rate of coarsening are consistent with equilibrium predictions from self-consistent field theory for the dependence of interfacial tension upon copolymer asymmetry. We show that the coarsening of cocontinuous blends can provide a method to quantify the reduction in interfacial tension due to block copolymer addition, which is difficult to measure by conventional methods.
Co-reporter:Shengxiang Ji;Zhengxi Zhu;Thomas R. Hoye
Macromolecular Chemistry and Physics 2009 Volume 210( Issue 10) pp:823-831
Publication Date(Web):
DOI:10.1002/macp.200900025
Co-reporter:Carlos R. Lopez-Barron
Macromolecular Symposia 2009 Volume 283–284( Issue 1) pp:348-353
Publication Date(Web):
DOI:10.1002/masy.200950941
Abstract
Geometrical parameters of the interface in fluorescently labeled polystyrene (FLPS)/styrene-ran-acrylonitrile compolymer (SAN) blends with cocontinuous morphology were obtained on the basis of differential geometry of 3D images. Images were analyzed for time evolution of interfacial area, average mean and Gaussian curvatures, curvature distributions and topology. Annealing of a symmetric (50/50 FLPS/SAN w/w) and a non symmetric (35/65) blend was monitored. For the symmetric blend a linear time evolution of the characteristic length along with a self similar growth of the microstructure, evidenced by the dynamic scaling of the curvature probability densities, were observed. For the non symmetric blend, the more elongated domains of the minor phase, namely FLPS, broke up producing zones with droplet-matrix structures coexisting with cocontinuous domains. Due to this morphological transition, dynamic scaling failed for the non symmetric blends. The number of holes on the interface, described by the genus, in a fixed sample volume decreases with time due to the growth of the microstructures and the formation of droplets.
Co-reporter:Hyunwoo Kim, Christopher W. Macosko
Polymer 2009 50(15) pp: 3797-3809
Publication Date(Web):
DOI:10.1016/j.polymer.2009.05.038
Co-reporter:Carlos R. Lopez-Barron and Christopher W. Macosko
Langmuir 2009 Volume 25(Issue 16) pp:9392-9404
Publication Date(Web):February 5, 2009
DOI:10.1021/la803450y
The coordinate transformation (CT) method was applied to measure the local curvature of the interface of an immiscible polymer blend made of fluorescently labeled polystyrene (FLPS) and styrene-ran-acrylonitrile copolymer (SAN). The CT method involves the local parametrization of the interface by a quadratic polynomial to compute the local values of the mean (H) and the Gaussian (K) curvatures. Distributions of the curvatures at different annealing times were obtained by measuring H and K at many (typically 107) points on the interface. Coarsening of a symmetric (50/50 w/w FLPS/SAN) and a nonsymmetric (35/65 w/w) blend was monitored. For the symmetric blend, two regimes of surface evolution were identified: in the early stage, the probability densities of the curvatures at various times were successfully scaled by a time-dependent characteristic length, i.e., interface area per unit volume (Q). This behavior has been previously observed in blends with morphologies created by a different mechanism, namely spinodal decomposition. In the late stage, the dynamic scaling failed and the time evolution of the interface slowed down. For the nonsymmetric blend, the domains of the minor phase (FLPS) were more elongated and they eventually broke up producing a composite microstructure with islands of drops within cocontinuous domains. We defined a “scaled” genus (G) to quantify the topology evolution of the blends during coarsening. Loss of connectivity was evidenced by a decrease of G with time for the nonsymmetric blend, while a constant value of this parameter indicated no change in topology during coarsening for the symmetric blend.
Co-reporter:Hyunwoo Kim and Christopher W. Macosko
Macromolecules 2008 Volume 41(Issue 9) pp:3317-3327
Publication Date(Web):April 10, 2008
DOI:10.1021/ma702385h
Nanocomposites reinforced with graphite platelets were compared to those with functionalized graphite sheets (FGS) prepared by partial pyrolysis of graphite oxide. Melt dispersion in poly(ethylene-2,6-naphthalate) (PEN) was quantified using a range of characterization techniques: electron microscopy, X-ray scattering, melt rheology, electrical conductivity, gas barrier, and mechanical properties. Conductivity percolation was obtained with as little as 0.3 vol % FGS, whereas 3 vol % was required for graphite. The threshold concentrations of FGS and graphite for rigidity percolation determined with melt rheology were in good agreement with conductivity percolation. Hydrogen permeability of PEN with 4 wt % FGS was decreased by 60% while the same amount of graphite reduced permeability only 25%. Structural differences between graphite and FGS were characterized with atomic force microscopy (AFM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The highly exfoliated morphology of FGS was maintained in the composites as revealed by electron microscopy and X-ray scattering while graphite layers remained stacked together even after melt processing. Even though the tensile stiffness and dimensional stability of PEN were improved, the extent of reinforcement with FGS for these two properties was not as significant. This was attributed to the wrinkled structure of FGS and atomistic defects.
Co-reporter:Thuy T. Chastek;Emily L. Que;Phil Jarzombeck;Andreas Stein
Journal of Applied Polymer Science 2007 Volume 105(Issue 3) pp:1456-1465
Publication Date(Web):23 APR 2007
DOI:10.1002/app.26315
A new synthetic clay, iC4-LMS, which is a lamellar mesostructured silicate with isobutyl groups covalently attached to silicate sheets, was synthesized with the goal to increase the compatibility of the inorganic sheets with polypropylene (PP) in a melt-blending process. The lamellar morphology of iC4-LMS was confirmed using X-ray diffraction and transmission electron microscopy. Based on 29Si and 13C{1H} CP-MAS NMR spectra, isobutyl functional groups were attached to at least 10 mol % of silicate tetrahedral sites in the inorganic layers. These surface groups mimic the subunits in the PP chains. Samples of iC4-LMS were mixed with several organic solvents and sonicated. The solvent most like PP, tetramethylpentadecane, had the highest viscosity, forming a gel which indicates very good dispersion of the clay. However, when iC4-LMS was melt-blended with PP, it did not show significant increase in rheology. This modest effect on rheology may arise from fracture of iC4-LMS layers as a result of the shear stresses during melt blending produced by the viscous PP. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007
Co-reporter:Christopher W. Macosko, Hyun K. Jeon, Thomas R. Hoye
Progress in Polymer Science 2005 Volume 30(8–9) pp:939-947
Publication Date(Web):August–September 2005
DOI:10.1016/j.progpolymsci.2005.06.003
Coupling functionalized polymers at the interface between them is a major route to compatibilize immiscible polymer blends. The reactively formed block or graft copolymers both stabilize morphology and enhance adhesion. Reactive coupling can also be used to increase the adhesion between coextruded films and for solvent-free synthesis of block copolymers, producing new nanostructured materials, not possible by normal synthetic routes. To produce materials with desirable final properties, it is important to predict how much copolymer will be formed under the processing conditions. This demands characterizing and understanding the interfacial reaction under processing conditions. This review focuses on our research that has investigated the major factors influencing the interfacial reaction such as the inherent reactivity of functional polymers, thermodynamic interaction between polymers, functional group location along a chain, and the effect of processing flows.
Co-reporter:Q.-W. Lu;C. W. Macosko;J. Horrion
Journal of Polymer Science Part A: Polymer Chemistry 2005 Volume 43(Issue 18) pp:4217-4232
Publication Date(Web):3 AUG 2005
DOI:10.1002/pola.20899
Amine (primary and secondary) functional polypropylenes were prepared by the melt blending of maleated polypropylenes with small diamines, including hexamethylenediamine (primary–primary diamine), p-xylylenediamine (primary–primary diamine), and N-hexylethylenediamine (primary–secondary diamine), at various diamine/anhydride molar ratios in a batch mixer and a twin-screw extruder. The experimental conversion data by Fourier transform infrared nearly agreed with the assumption of a complete reaction between the primary amine and anhydride. Chain extensions of the maleated polypropylenes by the diamines were monitored by the torques during mixing and further evaluated by rheological (dynamic shear rheometry) and mechanical measurements. We show that these amino polypropylenes are very effective adhesion promoters and compatibilizers of thermoplastic polyurethanes with polypropylene. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4217–4232, 2005
Co-reporter:Christopher W. Macosko;Thomas R. Hoye;Qi-Wei Lu
Journal of Polymer Science Part A: Polymer Chemistry 2002 Volume 40(Issue 14) pp:2310-2328
Publication Date(Web):22 MAY 2002
DOI:10.1002/pola.10310
Two model urethane compounds, dibutyl 4,4′-methylenebis(phenyl carbamate) (BMB) and dioctyl 4,4′-methylenebis(phenyl carbamate) (OMO) were prepared by capping 4,4′-methylenebis(phenyl isocyanate) with n-butanol and n-octanol, respectively. The reactions of the two model urethane compounds with several small monofunctional compounds as well as two model poly(ethylene glycols) were carried out with neat mixtures at elevated temperatures. The ranking of reactivity of the functional groups with the urethanes was determined as follows—primary amine > secondary amine ≫ hydroxyl ∼ acid ∼ anhydride ≫ epoxide. Nuclear magnetic resonance spectroscopy (NMR) was used for the quantitative analysis. Fourier transform infrared spectroscopy was used to complement the NMR analysis. Conversions of carbamate in each reaction were monitored over time at constant temperature (200 °C). The reactions between OMO and primary amine were conducted at 170, 180, 190, and 200 °C and best described with a second-order bimolecular reaction model. The rate constant was estimated to be 1.8 × 10−3 L · mol−1 · s−1 and activation energy 115 kJ · mol−1. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 2310–2328, 2002
Co-reporter:Jing Han, Zhengxi Zhu, Haitao Qian, Adam R. Wohl, ... Christopher W. Macosko
Journal of Pharmaceutical Sciences (October 2012) Volume 101(Issue 10) pp:4018-4023
Publication Date(Web):1 October 2012
DOI:10.1002/jps.23259
Johnson and Prud′homme (2003. AICHE J 49:2264–2282) introduced the confined impingement jets (CIJ) mixer to prepare nanoparticles loaded with hydrophobic compounds (e.g., drugs, inks, fragrances, or pheromones) via flash nanoprecipitation (FNP). We have modified the original CIJ design to allow hand operation, eliminating the need for a syringe pump, and we added a second antisolvent dilution stage. Impingement mixing requires equal flow momentum from two opposing jets, one containing the drug in organic solvent and the other containing an antisolvent, typically water. The subsequent dilution step in the new design allows rapid quenching with high antisolvent concentration that enhances nanoparticle stability. This new CIJ with dilution (CIJ‐D) mixer is a simple, cheap, and efficient device to produce nanoparticles. We have made 55 nm diameter β‐carotene nanoparticles using the CIJ‐D mixer. They are stable and reproducible in terms of particle size and distribution. We have also compared the performance of our CIJ‐D mixer with the vortex mixer, which can operate at unequal flow rates (Liu et al., 2008. Chem Eng Sci 63:2829–2842), to make β‐carotene‐containing particles over a series of turbulent conditions. On the basis of dynamic light scattering measurements, the new CIJ‐D mixer produces stable particles of a size similar to the vortex mixer. Our CIJ‐D design requires less volume and provides an easily operated and inexpensive tool to produce nanoparticles via FNP and to evaluate new nanoparticle formulation. © 2012 Wiley Periodicals, Inc. and the American Pharmacists Association J Pharm Sci 101:4018–4023, 2012
Co-reporter:Michael S. Owens, Madhu Vinjamur, L.E. Scriven, C.W. Macosko
Journal of Non-Newtonian Fluid Mechanics (October 2011) Volume 166(Issues 19–20) pp:1123-1128
Publication Date(Web):1 October 2011
DOI:10.1016/j.jnnfm.2011.06.008
Misting of liquids in forward roll coating is a problem under certain conditions. The relaxation time is known to influence misting but the fundamental mechanisms are not clear. A new mechanism for misting of dilute non-Newtonian liquids was proposed based on visualizations with a high-speed camera. With these liquids, filaments were created which sometimes transformed into beads-on-string structures and the beads were ejected as mist droplets when the structures broke. Misting was quantified by measuring sizes of the generated droplets, their count and mass concentration. The measurements were related to elasticity of the solutions through their relaxation times. Small levels of elasticity reduce the amount of misting, but higher levels lead to an increase.Highlights► A mechanism for misting with dilute polymer solutions in forward roll coating is visualized with a high-speed camera. ► Misting has been related to elasticity of the solutions through their relaxation times. ► Misting was quantified by measuring drop size, count and mass concentration. ► As relaxation times rise: larger and fewer drops are produced; mass concentration of mist falls to a minimum and then rises. ► Slight elasticity suppresses misting whereas more of it aggravates.
Co-reporter:Dawud H. Tan, Chunfeng Zhou, Christopher J. Ellison, Satish Kumar, Christopher W. Macosko, Frank S. Bates
Journal of Non-Newtonian Fluid Mechanics (August 2010) Volume 165(Issues 15–16) pp:892-900
Publication Date(Web):1 August 2010
DOI:10.1016/j.jnnfm.2010.04.012
Both melt viscosity (ηo) and elasticity (correlated here with the longest melt relaxation time λ1) were found to control the diameter distribution of meltblown fibers. Fibers were formed by melt blowing binary polystyrene (PS) blends containing widely differing component molecular weights using a custom-built laboratory apparatus. Varying the concentration and molecular weight of a high molecular weight PS provided independent control over ηo and λ1. These rheological parameters influence the average diameter (dav) and the distribution of diameters (coefficient of variation, CV) of meltblown fibers in different ways. Increasing ηo leads to an increase in dav but has little impact on CV. On the other hand, increasing λ1 beyond a threshold value reduces CV while simultaneously increasing dav. A one-dimensional slender-jet theoretical model with both upper convected Maxwell and Phan–Thien and Tanner constitutive equations was developed to investigate the influence of viscoelasticity and processing parameters on the properties of meltblown fibers. This model predicts a strong dependence of fiber diameter on the air shear stress and variations in fiber diameter with viscoelasticity that are in qualitative agreement with the experimental results. We believe these results suggest that carefully controlling the viscoelastic profile of polymers used in melt blowing is a viable approach for producing nanofibers with narrow fiber diameter distributions using current commercial equipment.
Co-reporter:Milana Trifkovic ; Aaron Hedegaard ; Kyle Huston ; Mehdi Sheikhzadeh
Macromolecules () pp:
Publication Date(Web):July 19, 2012
DOI:10.1021/ma300293v
The design of a porous membrane support layer derived from cocontinuous polymer blends is presented. We investigate the effect of blend composition, shear rate, residence time, and annealing time on the cocontinuous morphology of polyethylene (PE)/poly(ethylene oxide) (PEO) blends. Porous PE sheets were generated by water extraction of PEO and used as a support layer for gas separation membranes. The PE/PEO blends using nonfunctional and maleic anhydride functional PE (PE-g-MA) were mixed in a batch microcompounder and in a pilot plant scale corotating twin-screw extruder. Using PE-g-MA resulted in pore size reduction from 10 to 2 μm and suppression of coarsening of the morphology during further annealing of the blends due to formation of PE–PEO graft copolymers. Equilibrium interfacial tension, estimated by fitting the rheology of droplet blends to the Palierne viscoelastic droplet model, was 3 and 0.4 mN/m for PE/PEO and PE-g-MA/PEO systems, respectively. The specific interfacial area and phase size distribution were calculated from 3D images acquired by laser scanning electron microscopy (LSCM). We prepared gas separation membranes by solvent casting an acetone solution of ionic gel into porous PE sheets and discussed the effect of type of processing, average pore size, pore size distribution, and pore wall functionality on their performance.
.jpg)
![Silane, chlorotris[[(1R,2S,5R)-5-methyl-2-(1-methylethyl)cyclohexyl]oxy]-](http://img.cochemist.com/ccimg/191300/191216-17-8.png)
![Silane, chlorotris[[(1R,2S,5R)-5-methyl-2-(1-methylethyl)cyclohexyl]oxy]-](http://img.cochemist.com/ccimg/191300/191216-17-8_b.png)
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/26200/26161-42-2.png)
![Poly[oxy[(1S)-1-methyl-2-oxo-1,2-ethanediyl]]](http://img.cochemist.com/ccimg/26200/26161-42-2_b.png)
