Experimental study of primary radical generation in polyvinylalcohol/acrylamide (PVA/AA) based photopolymer material

Abstract

In the literature, several studies of the time varying photon absorption effects, which occur during the photo-initiation process in photopolymer materials, have been presented. Three primary mechanisms have been identified: (i) The photon absorption, (ii) the regeneration or recovery of the photosensitizer, and (iii) the photosensitizer bleaching. Based on the analysis of these mechanisms, the production of primary radicals can be physically described and modelled. In free radical photo-polymerization systems, the excited dye molecules induce the production of the primary radical, R•, which is a key factor that in determining how much monomer is polymerized. This in turn is closely related to the refractive index modulation, Δn, formed during holographic recording. In this article, by modifying the composition of a Polyvinylalcohol/Acrylamide (PVA/AA) based photopolymer material, i.e., excluding any co-initiator, the photo-kinetic behaviour of the material is greatly simplified, an experimental study is performed, which makes possible development and verification of a new model capable of accurately predicting the time varying concentration of primary radicals.