Polymerized ionic liquids (PolyILs) are an emerging class of polymer electrolytes which offer solutions to many problems in current battery technology. They combine the attractive features of ionic liquids with the mechanical strength of polymeric materials. However, a major obstacle in use of dry PolyILs is their low ionic conductivity at ambient temperature, which remains below the level required for many applications (ca. 10-3 S/cm). In this context, it has been shown that a significant enhancement of the ionic conductivity can be obtained by decoupling the ion motion from the segmental dynamics in polymers. We will review recent results obtained in this field using broadband dielectric spectroscopy, and discuss the microscopic parameters controlling ionic conductivity in PolyILs below Tg [1]. In particular, our detailed study of imidazolium-based PolyILs helped to unravel the interplay between nanostructure and ion conduction mechanism [2]. We also report first quasi-elastic neutron scattering experiments in these polymers suggesting the role of fast dynamics in assisting ion transport in the glassy state [3].[1] V. Bocharova and A.P. Sokolov, Macromolecules 2020, 53, 4141.[2] B. Doughty, A.C. Genix, I. Popov, B. Li, S. Zhao, T. Saito, D. Lutterman, R. Sacci, B.G. Sumpter, Z. Wojnarowska, V. Bocharova, Phys. Chem. Chem. Phys. 2019, 21, 14775.[3] V. Bocharova, A.C. Genix, A. Kisliuk, G. Sala, N.C. Osti, E. Mamontov, A. P. Sokolov, J. Phys. Chem. B 2020, 124, 10539.

Polymer nanocomposites (PNCs) are made by the dispersion of hard fillers in a polymer matrix, where the fillers are usually added to enhance mechanical properties. Such materials attract industrial interest and their investigation is essential for the improvement of their performances. The latter are strongly related to the structural properties of PNCs: the dispersion state of nanoparticles (NPs) in the polymer melt is governed by the mixing protocols (e.g., solid phase mixing or solvent casting) and thermodynamics of the system (i.e., particle miscibility) which influence both filler-filler and filler-polymer interactions.The present study concerns nanocomposites obtained using hydrophilic silica NPs dispersed in two different polymer matrices: 1) poly(2-vinylpyridine) forming attractive NP/polymer interfaces or 2) a weakly interacting styrene-butadiene (SB) rubber. In the first system, the dynamical properties of the interfacial layer surrounding NPs are obtained using broadband dielectric spectroscopy (BDS). Moreover, we propose an original approach combining small-angle scattering experiments of X-rays and neutrons and simulations to investigate the static properties. Only in ideally well-dispersed systems using pre-adsorption of the polymer chains, a static interfacial layer with a gradient of density extending over a thickness of ca. 2 nm is evidenced based on the analysis with a form-free density profile. This gradient is found to be generated by out-of-equilibrium packing and folding of the preadsorbed layer.In the second polydisperse and disordered SB system, we recently proposed a reverse Monte-Carlo analysis of the scattering data giving access to NP aggregate mass distributions. In opposition to the previous system, BDS experiments are not conclusive regarding the impact of the industrial filler on the segmental relaxation. Therefore, we used neutron spin-echo spectroscopy (NSE) and demonstrate – here for the first time – that incoherent NSE based on fully hydrogenated compounds can be used to resolve small modifications of the segmental dynamics of PNCs.

Polymers with dynamic (transient) bonds, often called associating polymers, have been attracting significant attention in recent years due to their unique viscoelastic properties, self-healing ability, and recyclability. Nevertheless, understanding the mechanisms and the factors controlling their macroscopic properties remains limited due to the higher complexity introduced by the dynamic bonds. In this study, small-angle X-ray scattering (SAXS), broadband dielectric spectroscopy (BDS), and rheology were applied to unravel the structure and dynamics of telechelic associating polymers with different molecular weights. SAXS measurements revealed phase separation of the functional end groups with an average cluster size of ∼2–3 nm and the distance between clusters controlled by the chain length. Borrowing the interfacial layer model analysis of BDS data from the polymer nanocomposite field, we demonstrated the presence of an interfacial polymer layer with a thickness of ∼0.7–0.9 nm surrounding these clusters. Rheological measurements showed quantitatively that the presence of the interfacial layer significantly alters the viscoelastic behavior of these materials, indicating the crucial role of the interfacial layer in defining the macroscopic mechanical properties of the studied telechelic materials. The presented results emphasize that phase separation of the functional groups in associating polymers leads to very significant changes of the viscoelastic properties, opening a promising avenue in the design of novel functional materials.

Due to their unique structural and mechanical properties, randomly cross-linked polymer networks play an important role in many different fields, ranging from cellular biology to industrial processes. In order to elucidate how these properties are controlled by the physical details of the network (e.g., chain-length and end-to-end distributions), we generate disordered phantom networks with different cross-linker concentrations C and initial densities ρ init and evaluate their elastic properties. We find that the shear modulus computed at the same strand concentration for networks with the same C, which determines the number of chains and the chain-length distribution, depends strongly on the preparation protocol of the network, here controlled by ρ init. We rationalize this dependence by employing a generic stress−strain relation for polymer networks that does not rely on the specific form of the polymer end-to-end distance distribution. We find that the shear modulus of the networks is a nonmonotonic function of the density of elastically active strands, and that this behavior has a purely entropic origin. Our results show that if short chains are abundant, as it is always the case for randomly cross-linked polymer networks, the knowledge of the exact chain conformation distribution is essential for correctly predicting the elastic properties. Finally, we apply our theoretical approach to literature experimental data, qualitatively confirming our interpretations.

We use ab initio molecular dynamics simulations to investigate the properties of the dry surface of pure silicaand sodium silicate glasses. The surface layers are defined based on the atomic distributions along the direction(z direction) perpendicular to the surfaces. We show that these surfaces have a higher concentration of danglingbonds as well as two-membered (2M) rings than the bulk samples. Increasing the concentration of Na 2 O reducesthe proportion of structural defects. From the vibrational density of states, one concludes that 2M rings have aunique vibrational signature at a frequency ≈850 cm −1 , compatible with experimental findings. We also findthat, due to the presence of surfaces, the atomic vibration in the z direction is softer than for the two otherdirections. The electronic density of states shows clearly the differences between the surface and interior and wecan attribute these to specific structural units. Finally, the analysis of the electron localization function allows toget insight on the influence of local structure and the presence of Na on the nature of chemical bonding in theglasses.

Supramolecular associations provide a promising route to functional materials with properties such as self-healing, easy recyclability or extraordinary mechanical strength and toughness. The latter benefit especially from the transient character of the formed network, which enables dissipation of energy as well as regeneration of the internal structures. However, recent investigations revealed intrinsic limitations in the achievable mechanical enhancement. This manuscript presents studies of a set of telechelic polymers with hydrogen-bonding chain ends exhibiting an extraordinarily high, almost glass-like, rubbery plateau. This is ascribed to the segregation of the associative ends into clusters and formation of an interfacial layer surrounding these clusters. An approach adopted from the field of polymer nanocomposites provides a quantitative description of the data and reveals the strongly altered mechanical properties of the polymer in the interfacial layer. These results demonstrate how employing phase separating dynamic bonds can lead to the creation of high-performance materials.