Poly(dimethylsiloxane) (PDMS) cross-linked films with different concentrations of micrometer-sized garnet particles were prepared through hydrosilylation reaction between a di-vinyl-terminated PDMS and a four-functional silane cross-linker in the presence of a Platinum catalyst. The garnet particles, consisting of micrometer-sized Ce doped Y 3 Al 5 O 12 particles commonly used on light converters (for solid state light devices, e.g. Light emitting diodes LEDs), were homogeneously and individually dispersed through the bulk of the cross-linked films for a concentration up to 20% in volume.
The effect of the garnet on the cross-linking of the composite films was investigated by in-situ ATR-FTIR Spectroscopy. When formulations with an excess of cross-linker were used the overall consumption of Si-H groups of the cross-linker is slowdown in the presence of the garnet. The same effect was observed for an increasing concentration of the garnet. This effect is attributed to a strong interaction of the catalyst with the garnet during the cross-linking process. The possible origins of this interaction are discussed.
NMR Imaging was used to investigate the cross-linked networks formed in the composite films. All the networks are homogeneous through the depth of the cross-linked composite films (approx. 5 mm resolution). The films prepared in the presence of the garnet particles showed similar relaxation behavior, regardless of the cross-linker concentration used in the initial formulation, contrary to previous results with PDMS cross-linked films. This behaviour is explained based on the presence of different type of chemical cross-links, resulting from the occurrence of hydrosilylation and secondary reactions, which are influenced by the interaction between the garnet particles and the catalyst.