Rayleigh-Brillouin and photon correlation spectroscopy of poly (n-hexyl methacrylate) near the glass transition, and light scattering and thermal characterization of hybrid nanoparticles

Poly (n-hexyl methacrylate) (pHMA) was studied with Rayleigh-Brillouin spectroscopy over the temperature range −11°C∼22°C. The Brillouin splitting steadily increased from 7.3 GHz to 9.2 GHz with decreasing temperature. PHMA exhibits large Brillouin linewidths, indicative of a broad distribution of relaxation times, compared to other poly alkyl methacrylates (pAMAs) near their respective glass transition temperatures. The sound velocity, longitudinal storage and loss moduli were calculated from Brillouin splitting and linewidth data, and the calculated values agree with values from other pAMAs and previous studies of pHMA. The Landau-Placzek ratios for this pHMA sample were lower than any other pAMA sample reported in the literature, suggestive of a high degree of optical purity.; Longer time dynamics were measured using photon correlation spectroscopy (PCS) over the temperature range 0.5°C∼52.5°C. The average relaxation times calculated from a Williams-Watts fit follow a VFTH temperature dependence, and the stretching parameter β decreases with decreasing temperature. The correlation functions were inverted using a non-negative least squares procedure. The α and β-relaxations appear to have merged in the distribution of relaxation times over this temperature range, and the temperature dependent width shows that there are at least two processes with separate temperature dependences. The maximum in the distribution of relaxation times exhibits the same temperature dependence as the frequency of maximum loss in dielectric data, suggesting that the same dynamic motions are being measured with the two techniques. In the distribution of relaxation times, a process at short times begins to appear in the correlation function window for low temperatures. This upturn at the lowest relaxation times is attributed to the γ-relaxation present in higher order methacrylate polymers.; Synthesis of hybrid materials is one mechanism used to integrate the mechanical properties of two different materials. Using atom transfer radical polymerization, different (co)polymers have been successfully tethered to spherical colloidal initiators. Solution phase dynamic light scattering of polysilsisquioxane-based hybrid materials demonstrates successful tethering of polystyrene (pS) and poly benzylacrylate (pBzA) blocks to the colloids. Particle sizes were compared with atomic force microscopy (AFM) and transmission electron microscopy images, and morphologies were determined using AFM. A scaling study was done with pS tethered to silica initiators. PCS measurements show a linear relationship between the molecular weight of tethered polymer and hydrodynamic radius of the particle. The linear relationship suggests that the high tethering density of polymer confines the chains to be more extended in solution. The effect of tethering and chain confinement on the T_g of tethered polymer was studied with differential scanning calorimetry. The increase in T_g from the bulk value was as high as 13°C.