Side-chain motions in poly(methyl methacrylate) + SiO_2 hosts of fluorecent dyes studied by thermally stimulated discharge currents: effects of confinement and blending

摘要

The thermally stimulated discharge (TSD) currents technique has been used to study different types of inter- and intra-molecular interactions between the components in poly(methyl methacrylate) (PMMA)-based systems. The TSD current signal of the side-chain dielectric beta relaxation mode of PMMA has been comparatively studied in bulk PMMA, PMMA polymerized in-situ mesoporous silica-gel, and these matrices in the presence of polar and ionic (rhodamine 6G/Cl~-) or non-polar (perylene derivatives) fluorescent dyes. The analysis of the TSD responses by means of partial heating and thermal sampling techniques indicates that polymer's confinement in SiO_2 induces firstly, an increase of the distributed energy barriers of the beta relaxation mode, and secondly, an enhancement of the contribution of the faster relaxation modes (at T < T_max(beta)) in the overall strength of the beta mechanism. Basic features of the bands (i.e. peak maximum and distribution of activation energies) exclude the occurrence of strong interactions between the perylene derivatives and the carbonyl groups of PMMA. To contrary, coupling effects appear between the motions of ghe side-groups of PPMA and rhodamine 6G. The results are interpreted in view of counteracting structural (e.g. modification of the polymer's free volume) and surface (hydrogen-bond interphase interactions) effects of confinement and blending on the relaxation dynamics of the pendant groups.