The segmental dynamics of 1.5-2.0 nm polymer films confined between parallel solid surfaces is investigated with dielectric spectroscopy in polymer/silicate intercalated nanocomposites. The confinement effect is evident by the observation of a mode, much faster than the bulk-polymer alpha relaxation and exhibiting much weaker temperature dependence. This is discussed in relation to either the interlayer spacing restricting the cooperative volume of the alpha relaxation or to the dominance of the more mobile interphase regions as predicted by simulations; the data qualitatively support the former.

Multiarm star polymers represent a valuable model system for investigating the dynamics of tethered chains, spherical brushes, or grafted colloidal spheres. Because of their topology, the multiarm stars exhibit a nonuniform monomer density distribution leading to a core−shell morphology, which is responsible for their rich dynamic structure. When the stars interpenetrate, they exhibit liquidlike (macrocrystalline) order due to the enhanced osmotic pressure which balances the entropic stretching of the near-core segments and the excluded volume effects. Using dynamic light scattering, we probe three relaxation modes in the semidilute regime:  (i) the fast cooperative diffusion, which is characteristic of their polymeric nature (entangled shell arms); (ii) the self-diffusion of the stars (essentially cores), probed because of finite functionality polydispersity, as confirmed by independent pulsed-field gradient NMR measurements; and (iii) the structural mode, which corresponds to rearrangements of the ordered stars. We develop a mean-field scaling theory, which captures all features observed experimentally with good quantitative agreement. The two slow modes, ii and iii, are reminiscent of the behavior of interacting hard colloidal spheres and are governed essentially by the same physics. We propose these model soft spheres as appropriate vehicles for unifying the descriptions of the dynamics of polymers and soft colloidal dispersions.

We report on the segmental dynamics of the binary polymer blend polystyrene (PS)/poly (methylphenylsiloxane) (PMPS) in the two-phase region using dielectric spectroscopy that essentially probes the PMPS component. Based on the experimental orientation relaxation functions, the average glass transition temperature Tg controls phase separation. When the spinodal temperature Ts exceeds Tg, the PMPS segmental relaxation displays two distinct decays characteristic of a merely pure and a mixed, roughly at the initial composition, PMPS regions. On the contrary, when Ts falls in the proximity of Tg, the PMPS relaxation is strongly nonexponential and its average time reflects mixed regions rich in PMPS due to incomplete phase separation, which drives only the glassy phase out of local thermodynamic equilibrium. Distinct morphological differences in the two-phase state of these blends, inferred from their segmental dynamics, are revealed by transmission electron microscopy.