Segmental relaxation in semicrystalline polymers: a mean field model for the distribution of relaxation times in confined regimes

The effect of confinement in the segmental relaxation of polymers is considered. On the basis of a thermodynamic model we discuss the emerging relevance of the fast degrees of freedom in stimulating the much slower segmental relaxation, as an effect of the constraints at the walls of the amorphous regions. In the case that confinement is due to the presence of crystalline domains, a quasi-poissonian distribution of local constraining conditions is derived as a result of thermodynamic equilibrium. This implies that the average free energy barrier $\Delta F$ for conformational rearrangement is of the same order of the dispersion of the barrier heights, $\delta (\Delta F)$, around $\Delta F$. As an example, we apply the results to the analysis of the $\alpha$-relaxation as observed by dielectric broad band spectroscopy in semicrystalline poly(ethylene terephthalate) cold-crystallized from either an isotropic or an oriented glass. It is found that in the latter case the regions of cooperative rearrangement are significantly larger than in the former.Comment: 10 pages, 4 figures .ep

Self-assembly of thermo and light responsive amphiphilic linear dendritic block copolymers

The synthesis and structural characterization of a new dual responsive linear-dendritic block copolymer (LDBC) is presented. The LDBC is constituted by a thermoresponsive linear block from polymethacrylate of oligo- and diethylene glycol, and a light responsive den- dron block of bis-MPA decorated at the periphery with 4-isobutyloxyazobenzene and alkyl chains in a 50:50 M ratio. Blocks are coupled together by copper(I) catalyzed alkyne–azide cycloaddition (CuAAC). The ability of the LDBC to form vesicle self-assemblies in water is described, as well as the effect of light and temperature on the vesicles morphology, on the basis of transmission electron microscopy (TEM), dynamic light scattering (DLS) and UV–vis spectroscopy studies. The effect of UV light and temperature on the vesicles struc- ture by SAXS and WAXS conducted on real time is also presented. Finally, the potential use of the vesicles to load and stimuli controlled release of small fluorescent molecules is probed

Confined dynamics in poly(ethylene terephthalate): A coherent and incoherent neutron scattering study

We show that the combination of dielectric relaxation with neutron spin echo and incoherent neutron backscattering measurements performed in deuterated and protonated poly(ethylene terephthalate) suggests that the intrinsic dynamics of semicrystalline polymers occurs in an homogeneous scenario, similar to that valid to describe the dynamics of totally amorphous polymers. The quasielastic neutron scattering data are satisfactorily described by a theoretical model that considers that the proton mobility follows a random jump-diffusion in a restricted environment

Restricted dynamics in semicrystalline aromatic polyesters

none5Titolo della collana: PMSE PreprintsnoneA. Sanz; A. Nogales; N. Lotti; S.S Funari; T.A. EzquerraA. Sanz; A. Nogales; N. Lotti; S.S Funari; T.A. Ezquerr