Combining neutron diffraction, neutron spin echo, differential scanning calorimetry and dielectric spectroscopy we have investigated the structure and dynamics of poly(n-butyl methacrylate) (PBMA) and poly(n-hexyl methacrylate) (PHMA).Signatures of the occurrence of a glass-transition associated to the freezing of the inter-molecular correlations within alkyl nanodomains are present in the structural data. Exploiting isotopic labeling, neutron scattering has revealed collective dynamics at the main-chain and side-group levels for both polymers and the self-motions of hydrogen atoms in the side-groups of PHMA, adding valuable microscopic information to comprehensive relaxation maps and putting the relaxation results into a perspective. Moreover, we find exotic dynamical behavior for the side-groups, char-acterized by extremely stretched (nearly logarithmic-like) decays of the correlation functions. For PHMA, a complete dynamical decoupling of side-group dynamics from the main-chain motions is found. The side-groups of this polymer show an extremely 'strong' temperature dependence of the structural relaxation time and much faster characteristic times for self than collective motions. The analogies found between the self-motions of the side-group H-atoms in PHMA and the γ-relaxation process in semicrystalline polyethylene (PE) strengthen the picture of confined PElike dynamics within alkyl nanodomains. We discuss possible origins for the observed phenomenology.

We explore the effects of chain size on the structure and dynamics of ethylene glycol (EG) and poly(ethylene oxide) (PEO) intercalated in graphite oxide (GO). To this end, EG as well as a PEO series of increasing chain length have been studied by means of high-resolution inelastic neutron spectroscopy. The neutron experiments are complemented by X-ray diffraction, differential scanning calorimetry, Fourier-transform infrared spectroscopy, and Raman scattering. We find that EG is accommodated in a layer of thickness ∼3 Å within the GO substrate and adopts a preferential, yet largely disordered, gauche conformation. Longer PEO chains give rise to a layer thickness in the range ∼3.0−3.4 Å characterized by planar zigzag (trans−trans−trans) conformations. Moreover, we observe a strong reduction of vibrational motions for the confined EG and polymer phases, as clearly evidenced by the disappearance, shift, and/or broadening of mode-specific inelastic neutron scattering spectral features, as well as by the complete suppression of crystallization. All of these effects are surprisingly insensitive to the length of the PEO chains.

The behavior of water dynamics confined in hydrated calcium silicate hydrate (C-S-H) gel has been investigated using broadband dielectric spectroscopy (BDS; 10(-2)-10(6) Hz) in the low-temperature range (110-250 K). Different water contents in C-S-H gel were explored (from 6 to 15 wt%) where water remains amorphous for all the studied temperatures. Three relaxation processes were found by BDS (labeled 1 to 3 from the fastest to the slowest), two of them reported here for the first time. We show that a strong change in the dielectric relaxation of C-S-H gel occurs with increasing hydration, especially at a hydration level in which a monolayer of water around the basic units of cement materials is predicted by different structural models. Below this hydration level both processes 2 and 3 have an Arrhenius temperature dependence. However, at higher hydration level, a non-Arrhenius behavior temperature dependence for process 3 over the whole accessible temperature range and, a crossover from low-temperature Arrhenius to high-temperature non-Arrhenius behavior for process 2 are observed. Characteristics of these processes will be discussed in this work.

The determination of the net charge and size of microgel particles as a function of their concentration, as well as the degree of association of ions to the microgel backbone, has been pursued in earlier studies mainly by scattering and rheology. These methods suffer from contributions due to inter-particle interactions that interfere with the characterization of single-particle properties. Here we introduce dielectric spectroscopy as an alternative experimental method to characterize microgel systems. The advantage of dielectric spectroscopy over other experimental methods is that the polarization due to mobile charges within a microgel particle is only weakly affected by inter-particle interactions. Apart from electrode polarization effects, experimental spectra on PNIPAM-co-AA [poly(N-isopropylacrylamide-co-acrylic acid)] ionic microgel particles suspended in de-ionized water exhibit three well-separated relaxation modes, which are due to the polarization of the mobile charges within the microgel particles, the diffuse double layer around the particles, and the polymer backbone. Expressions for the full frequency dependence of the electrode-polarization contribution to the measured dielectric response are derived, and a theory is proposed for the polarization resulting from the mobile charges within the microgel. Relaxation of the diffuse double layer is modeled within the realm of a cell model. The net charge and the size of the microgel particles are found to be strongly varying with concentration. A very small value of the diffusion coefficient of ions within the microgel is found, due to a large degree of chemical association of protons to the polymer backbone.

Self-propelling microparticles are often proposed as synthetic models for biological microswimmers, yet they lack the internally regulated adaptation of their biological counterparts. Conversely, adaptation can be encoded in larger-scale soft-robotic devices but remains elusive to transfer to the colloidal scale. Here, we create responsive microswimmers, powered by electro-hydrodynamic flows, which can adapt their motility via internal reconfiguration. Using sequential capillary assembly, we fabricate deterministic colloidal clusters comprising soft thermo-responsive microgels and light-absorbing particles. Light absorption induces preferential local heating and triggers the volume phase transition of the microgels, leading to an adaptation of the clusters’ motility, which is orthogonal to their propulsion scheme. We rationalize this response via the coupling between self-propulsion and variations of particle shape and dielectric properties upon heating. Harnessing such coupling allows for strategies to achieve local dynamical control with simple illumination patterns, revealing exciting opportunities for developing tactic active materials.