Photokinetic study of Irgacure 784 dye in an epoxy resin photopolymer

Abstract

Photopolymers are promising as holographic recording media as they are inexpensive, versatile materials, which can be made sensitive to a broad range of wavelengths. A deeper understanding of the processes, which occur during holographic grating formation in photopolymers, is necessary in order to develop a fully comprehensive model, which represents their behaviour. One of these processes is photo-initiation, whereby a photon is absorbed by a photosensitiser producing free radicals, which can initiate free radical polymerisation. These free radicals can also participate in polymer chain termination (primary termination) and it is therefore necessary to understand their generation in order to predict the temporally varying kinetic effects present during holographic grating formation. In this paper, a study of the photoinitiation mechanisms of Irgacure 784 dye, in an epoxy resin matrix, is carried out. This is achieved by analysing the temporal evolution of a series of simultaneously captured experimental transmittance curves, captured at different wavelengths, but at the same location, to enable the change in photon absorption during exposure to be estimated. We report on the experimental results and present a theoretical model to predict the physically observed behaviour.