The effect of water content on silica nanoparticles was examined by thermogravimetry analysis (TGA), broadband dielectric spectroscopy (from 10 −2 to 10 7 Hz), and differential scanning calorimetry for a wide temperature range (110−250 K). Silica nanoparticles were dried and rehydrated at different water levels to determine the critical factors affecting the dielectric response. The dynamics of both hydration water and hydrated silanol groups were addressed. Whereas hydration water dynamics depend on the water content, the dynamics corresponding to hydrated silanol groups are almost water independent once the maximum hydroxylation level is reached. In addition, we determined that during hydration water molecules prefer to form clusters instead of filling a complete layer around the particles. Finally, we observed that contrary to other water containing systems, the corresponding relaxation times of water molecules do not show any crossover (from high-T super-Arrhenius to low-T Arrhenius behavior).

A small-angle neutron scattering (SANS) investigation of matrix chain deformation in an especially designed composite model system for a filled rubber-elastic network is presented. SANS experiments on the structure of polyisoprene homopolymer chains introduced into a well-microphaseseparated triblock polyisoprene-polystyrene-polyisoprene (PI-PS-PI) system of the ABA type are reported. Use is made of the phase-and composition-matching techniques. The data are described in terms of the scattering behavior of the corresponding pure polyisoprene network at larger microscopic than macroscopic strains. The results confirm the model for the strain enhancement in reinforced networks and give the first direct microscopic insights into the mechanisms of reinforcement. A complementary small-angle X-ray scattering (SAXS) study yields all relevant geometrical parameters of the model filler and its detailed behavior under strain.

We present in this work a systematic study to analyze the influence of water and filler content on the dielectric response of silica-filled rubber compounds. For nanoparticle-filled polymers an additional dielectric process is usually observed in the loss dielectric spectra at frequencies lower than the alpha (α) or segmental relaxation. This process has generated some controversy in the literature due to the different (sometimes contradictory) interpretations given to explain its physical origin. We demonstrate, by means of dielectric spectroscopy in combination with thermal analysis, that this low-frequency process is compatible with a MWS process enhanced by the presence of water molecules at the silica surface. We show that the frequency of the maximum for this process is strongly affected by the amount of water attached to the silica particles. The dielectric response of the MWS process is rationalized by means of a simple interlayer model (IL). In addition, we also study the influence of water and filler content on the segmental dynamics and discuss possible mechanisms for the filler−polymer interaction.

Robust quantitative cross-link density characterization becomes necessary for the complete understanding of the structure and optimization of final properties of rubber compounds for industrial applications. A combination of different experimental techniques have been used to establish the quantitative consistency on the correlations between the results obtained by the individual methods within a reliable unique (physically based) platform reclined on the concept of rubber elasticity that considers the impact of entanglements in technical rubbers. The contribution of cross-links and elastically active entanglements to mechanical properties has been quantified by the analysis of uniaxial stress–strain measurements by means of the extended tube model of rubber elasticity. In a complementary manner, rubber network structure has also been investigated by state-of-the-art multiple-quantum low-field NMR experiments and classical T1 and T2 relaxation measurements. In addition, equilibrium swelling data were analyzed by the classical phantom and Flory–Rehner limits as well as by applying the theoretical approach proposed by Helmis, Heinrich, and Straube that takes into account topological constraints during swelling. Correlations among these complementary techniques have been reported, and the interpretation of the obtained differences is addressed. The baseline study focuses on unfilled NR, setting the basis for the investigation of unfilled SBR matrices and filled rubbers.

A theoretical and experimental investigation of the SANS structure factor of labeled triblock HDH copolymer chains, randomly cross-linked into a network, is presented. We combine the RPA method for the consideration of the strong interchain correlations and the tube model with a harmonic deformation dependent constraining potential, modeling the action of cross-links and entanglements. With this approach a successful description of the scattering behavior under strain is achieved. The sensitivity of the method allows the detection of chain splittings during cross-linking with peroxides.