Polymer nanocomposites (PNCs) are important materials that are widely used in many current technologies and potentially have broader applications in the future due to their excellent property tunability, light weight, and low cost. However, expanding the limits in property enhancement remains a fundamental scientific challenge. Here, we demonstrate that well-dispersed, small (diameter ∼1.8 nm) nanoparticles with attractive interactions lead to unexpectedly large and qualitatively different changes in PNC structural dynamics in comparison to conventional nanocomposites based on particles of diameters ∼10–50 nm. At the same time, the zero-shear viscosity at high temperatures remains comparable to that of the neat polymer, thereby retaining good processability and resolving a major challenge in PNC applications. Our results suggest that the nanoparticle mobility and relatively short lifetimes of nanoparticle-polymer associations open qualitatively different horizons in the tunability of macroscopic properties in nanocomposites with a high potential for the development of advanced functional materials.Keywords: apparent disentanglement; fragility; glass transition; polymer nanocomposites; small nanoparticles;

•Novel solid polymer electrolyte candidates have been synthesized using ROMP.•The polymers demonstrate high lithium salt solubility without crystallization.•Ionic conductivity has been separated from segmental dynamics by 6–7 orders.•The results suggest the necessity to both lower Tg and improve decoupling.In order to design more effective solid polymer electrolytes, it is important to decouple ion conductivity from polymer segmental motion. To that end, novel polymers based on oxanorbornene dicarboximide monomers with varying lengths of oligomeric ethylene oxide side chains have been synthesized using ring opening metathesis polymerization. These unique polymers have a fairly rigid and bulky backbone and were used to investigate the decoupling of ion motion from polymer segmental dynamics. Ion conductivity was measured using broadband dielectric spectroscopy for varying levels of added lithium salt. The conductivity data demonstrate six to seven orders of separation in timescale of ion conductivity from polymer segmental motion for polymers with shorter ethylene oxide side chains. However, commensurate changes in the glass transition temperatures Tg reduce the effect of decoupling in ion conductivity and lead to lower conductivity at ambient conditions. These results suggest that both an increase in decoupling and a reduction in Tg might be required to develop solid polymer electrolytes with high ion conductivity at room temperature.Download high-res image (123KB)Download full-size image

We demonstrate the unprecedented chemical imaging of individual constituents in a four-component sample made of several carbon allotropes: single-wall carbon nanotubes, graphene oxide, C60 fullerene, and an organic residue. This represents a significant advance with respect to previous works that were mainly limited to systems with one or two components having very different chemical composition. Despite the spectral and spatial overlap from different components, plasmon-based nanospectroscopy allows the discrimination of all individual carbon nanomaterials here investigated. Among other physical insights such as doping observed in carbon nanotubes, the detailed chemical imaging of graphene oxide reveals higher defect concentration at the flake edges similarly to the case of graphene. We found that the organic residue has either low adsorption or lack of resonant enhancement on GO, in contrast to graphene, suggesting a decreased van der Waals interaction. This report paves the way for routine nanoscale analysis of complex carbon systems with spatial resolution of 15 nm and below.

Combining broadband impedance spectroscopy, differential scanning calorimetry, and nuclear magnetic resonance we analyzed charge and mass transport in two polymerized ionic liquids and one of their monomeric precursors. In order to establish a general procedure for extracting single-particle diffusivity from their conductivity spectra, we critically assessed several approaches previously employed to describe the onset of diffusive charge dynamics and of the electrode polarization in ion conducting materials. Based on the analysis of the permittivity spectra, we demonstrate that the conductivity relaxation process provides information on ion diffusion and the magnitude of cross-correlation effects between ionic motions. A new approach is introduced which is able to estimate ionic diffusivities from the characteristic times of conductivity relaxation and ion concentration without any adjustable parameters. This opens the venue for a deeper understanding of charge transport in concentrated and diluted electrolyte solutions.

We present an overview of protein dynamics based mostly on results of neutron scattering, dielectric relaxation spectroscopy and molecular dynamics simulations. We identify several major classes of protein motions on the time scale from faster than picoseconds to several microseconds, and discuss the coupling of these processes to solvent dynamics. Our analysis suggests that the microsecond backbone relaxation process might be the main structural relaxation of the protein that defines its glass transition temperature, while faster processes present some localized secondary relaxations. Based on the overview, we formulate a general picture of protein dynamics and discuss the challenges in this field.

•Three dielectric relaxations are identified for hydrated lysozyme and myoglobin.•The Main process is ascribed to a coupled protein–hydration water relaxation.•The Slow process is ascribed to large scale domain-like motions of proteins.•Anomalous intensity Slow process is suggested to be related to glass transition.We present detailed dielectric spectroscopy studies of dynamics in two hydrated proteins, lysozyme and myoglobin. We emphasize the importance of explicit account for possible Maxwell–Wagner (MW) polarization effects in protein powder samples. Combining our data with earlier literature results, we demonstrate the existence of three major relaxation processes in globular proteins. To understand the mechanisms of these relaxations we involve literature data on neutron scattering, simulations and NMR studies. The faster process is ascribed to coupled protein–hydration water motions and has relaxation time ~ 10–50 ps at room temperature. The intermediate process is ~ 102–103 times slower than the faster process and might be strongly affected by MW polarizations. Based on the analysis of data obtained by different experimental techniques and simulations, we ascribe this process to large scale domain-like motions of proteins. The slowest observed process is ~ 106–107 times slower than the faster process and has anomalously large dielectric amplitude Δε ~ 102–104. The microscopic nature of this process is not clear, but it seems to be related to the glass transition of hydrated proteins. The presented results suggest a general classification of the relaxation processes in hydrated proteins.

We present the discovery of an unusually large isotope effect in the structural relaxation and the glass transition temperature Tg of water. Dielectric relaxation spectroscopy of low-density as well as of vapor-deposited amorphous water reveal Tg differences of 10 ± 2 K between H2O and D2O, sharply contrasting with other hydrogen-bonded liquids for which H/D exchange increases Tg by typically less than 1 K. We show that the large isotope effect and the unusual variation of relaxation times in water at low temperatures can be explained in terms of quantum effects. Thus, our findings shed new light on water's peculiar low-temperature dynamics and the possible role of quantum effects in its structural relaxation, and possibly in dynamics of other low-molecular-weight liquids.

There is tremendous interest in understanding the role that secondary structure plays in the rigidity and dynamics of proteins. In this work we analyze nanomechanical properties of proteins chosen to represent different secondary structures: α-helices (myoglobin and bovine serum albumin), β-barrels (green fluorescent protein), and α + β + loop structures (lysozyme). Our experimental results show that in these model proteins, the β motif is a stiffer structural unit than the α-helix in both dry and hydrated states. This difference appears not only in the rigidity of the protein, but also in the amplitude of fast picosecond fluctuations. Moreover, we show that for these examples the secondary structure correlates with the temperature- and hydration-induced changes in the protein dynamics and rigidity. Analysis also suggests a connection between the length of the secondary structure (α-helices) and the low-frequency vibrational mode, the so-called boson peak. The presented results suggest an intimate connection of dynamics and rigidity with the protein secondary structure.

We present analysis of nanosecond-picosecond dynamics of Green Fluorescence Protein (GFP) using neutron scattering data obtained on three spectrometers. GFP has a β-barrel structure that differs significantly from the structure of other globular proteins and is thought to result in a more rigid local environment. Despite this difference, our analysis reveals that the dynamics of GFP are similar to dynamics of other globular proteins such as lysozyme and myoglobin. We suggest that the same general concept of protein dynamics may be applicable to all these proteins. The dynamics of dry protein are dominated by methyl group rotations, while hydration facilitates localized diffusion-like motions in the protein. The latter has an extremely broad relaxation spectrum. The nanosecond–picosecond dynamics of both dry and hydrated GFP are localized to distances of ∼1–3.5 Å, in contrast to the longer range diffusion of hydration water.

Despite significant experimental and theoretical efforts, a fundamental understanding of how the chemical structure influences various dynamic processes in glass-forming materials and polymers remains a topic of active discussion. The present study analyzes the influence of polar interactions on the temperature dependences of segmental and chain dynamics in polymers. We found that segmental dynamics slow down (the glass transition temperature Tg increases) and have steeper temperature dependence (higher fragility index m) when a polar group is attached directly to the polymer backbone. However, when a polar group is separated from the backbone by a side group, both Tg and m become complex functions of the monomer’s polarity and the relative position of the polar group. Our analysis revealed unexpected effect of polar interactions on chain dynamics: chain modes in polar polymers are coupled to the segmental dynamics stronger than in nonpolar polymers with similar fragilities. This results in a steeper temperature dependence of chain dynamics in polar polymers. How the polar interactions affect the coupling of chain and segmental modes remains unclear.

A self-complementary heteroditopic molecule composed of thymine and diamidopyridine end groups and a flexible aliphatic interconnecting chain has been synthesized. The glassy dynamics of this hydrogen-bonded supramolecule have been investigated by using dielectric and rheological measurements, in combination with infra-red spectroscopy and solid-state 13C NMR experiments. Decoupling of main dielectric relaxation from viscosity has been found in the vicinity of the glass transition and the temperature dependence of viscosity appears to be stronger than that of dielectric relaxation. The unusual dynamic decoupling phenomenon is ascribed to the chemical/dynamic heterogeneity and formation of hydrogen bonds in the supramolecules.

Although fragility of glass forming liquids is traditionally related to cooperativity in molecular motion, the connection between those parameters remains unclear. In this paper we present the estimates of cooperativity (heterogeneity) length scale ξ obtained from the boson peak spectra. We demonstrate that ξ agrees well with the dynamic heterogeneity length scale for the structural relaxation estimated by 4-dimensional NMR, justifying the use of ξ. Presented analysis of large number of materials reveals no clear correlation between ξ and fragility. However, there is a strong correlation between the cooperativity volume ξ3 and the activation volume measured at Tg. This observation suggests that only the volume (pressure) dependence of structural relaxation time correlates directly with the cooperativity size. However, the pure thermal (energetic) contribution to the structural relaxation, the so-called isochoric fragility, exhibits no correlation to the heterogeneity length scale ξ, or the amount of structural units in ξ3. The presented results call for a revision of traditional view on the role of cooperativity/heterogeneity in structural relaxation of glass forming systems.

Using broadband dielectric spectroscopy, we studied the temperature dependence of ionic conductivity and structural relaxation in a number of polymers. We demonstrate that temperature dependence of ionic conductivity can be decoupled from structural relaxation in a material specific way. We show that the strength of the decoupling correlates with the steepness of the temperature dependence of structural relaxation in the polymer, i.e., with its fragility. We ascribe the observed result to stronger frustration in chain packing characteristic for more fragile polymers. We speculate that employment of more fragile polymers might lead to design of polymers with higher ionic conductivity.

Presented analysis of neutron, mechanical, and MD simulation data available in the literature demonstrates that the dynamic bead size (the smallest subchain that still exhibits the Rouse-like dynamics) in most of the polymers is significantly larger than the traditionally defined Kuhn segment. Moreover, our analysis emphasizes that even the static bead size (e.g., chain statistics) disagrees with the Kuhn segment length. We demonstrate that the deficiency of the Kuhn segment definition is based on the assumption of a chain being completely extended inside a single bead. The analysis suggests that representation of a real polymer chain by the bead-and-spring model with a single parameter C∞ cannot be correct. One needs more parameters to reflect correctly details of the chain structure in the bead-and-spring model.

•Ionic transport and segmental dynamics in polymers can be strongly decoupled.•Degree of decoupling is controlled by frustration in local packing (fragility).•Polyethers have intrinsic limitations due to coupled ion and segmental dynamics.•Decoupling approach provides a new paradigm for design of polymer electrolytes.Despite potential significant advantages of polymer based batteries, the poor ionic conductivity of dry polymer electrolytes at ambient and low temperatures has limited their application. This review describes the approach for improving conductivity by decoupling ionic transport from polymer segmental relaxation. It is emphasized that the decoupling approach is the key for design of superionic polymer electrolytes.

We studied the dynamics of hydrated tRNA using neutron and dielectric spectroscopy techniques. A comparison of our results with earlier data reveals that the dynamics of hydrated tRNA is slower and varies more strongly with temperature than the dynamics of hydrated proteins. At the same time, tRNA appears to have faster dynamics than DNA. We demonstrate that a similar difference appears in the dynamics of hydration water for these biomolecules. The results and analysis contradict the traditional view of slaved dynamics, which assumes that the dynamics of biological macromolecules just follows the dynamics of hydration water. Our results demonstrate that the dynamics of biological macromolecules and their hydration water depends strongly on the chemical and three-dimensional structures of the biomolecules. We conclude that the whole concept of slaving dynamics should be reconsidered, and that the mutual influence of biomolecules and their hydration water must be taken into account.

We present a detailed analysis of the picosecond-to-nanosecond motions of green fluorescent protein (GFP) and its hydration water using neutron scattering spectroscopy and hydrogen/deuterium contrast. The analysis reveals that hydration water suppresses protein motions at lower temperatures (<∼200 K), and facilitates protein dynamics at high temperatures. Experimental data demonstrate that the hydration water is harmonic at temperatures <∼180–190 K and is not affected by the proteins’ methyl group rotations. The dynamics of the hydration water exhibits changes at ∼180–190 K that we ascribe to the glass transition in the hydrated protein. Our results confirm significant differences in the dynamics of protein and its hydration water at high temperatures: on the picosecond-to-nanosecond timescale, the hydration water exhibits diffusive dynamics, while the protein motions are localized to <∼3 Å. The diffusion of the GFP hydration water is similar to the behavior of hydration water previously observed for other proteins. Comparison with other globular proteins (e.g., lysozyme) reveals that on the timescale of 1 ns and at equivalent hydration level, GFP dynamics (mean-square displacements and quasielastic intensity) are of much smaller amplitude. Moreover, the suppression of the protein dynamics by the hydration water at low temperatures appears to be stronger in GFP than in other globular proteins. We ascribe this observation to the barrellike structure of GFP.