Dynamic glass transition of filled polysiloxane upon electron irradiation

Abstract : The influence of radiation-induced crosslinking on the molecular mobility of a filled silicone elastomer near the glass transition (α-relaxation) was analyzed using broadband dielectric spectroscopy. Samples of the isolated polysiloxane matrix (neat) were also studied so as to assess the filler influence on the evolution of the α-relaxation. A slowing-down of the segmental dynamics was observed with increasing ionizing dose. It was ascribed to the relaxing dipoles losing degrees of freedom as a result of network stiffening. An enhancement of intermolecular coupling, associatedwith the cooperativity of the α-relaxation,was deduced fromthe dielectric analysis. Similar observations were made in the past with chemically crosslinked polysiloxanes. This study evidenced that even though the crosslinks formed upon chemical crosslinking (mainly Si\\CH2\\CH2\\Si) differ in nature from those formed upon irradiation (mainly SiO3 and SiO4), they affect the dynamic glass transition in a very similar way. The filler influence on the dynamic glass transition was also studied upon irradiation. One of the main outcomes of this study is the fading of the filler-related effect in themost irradiated samples: both the shape and dynamics of the α-relaxation were identical in the most highly irradiated neat and filled samples.