Side-chain motions in poly(methyl methacrylate)+SiO2 hosts of fluorescent dyes studied by thermally stimulated discharge currents: effects of confinement and blending

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 β 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 polymerʹs confinement in SiO2 induces, firstly, an increase of the distributed energy barriers of the β relaxation mode, and secondly, an enhancement of the contribution of the faster relaxation modes (at T<Tmax(β)) in the overall strength of the β mechanism. Basic features of the β 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 the side-groups of PMMA and rhodamine 6G. The results are interpreted in view of counteracting structural (e.g. modification of the polymerʹs free volume) and surface (hydrogen-bond interphase interactions) effects of confinement and blending on the relaxation dynamics of the pendant groups.