Recent developments in the NPDD model

Abstract

An understanding of the photochemical and photo-physical processes, which occur during photo-polymerization, is of extreme importance when attempting to improve a photopolymer material's performance for a given application. Recent work carried out on the modeling of photopolymers during-and post-exposure, has led to the development of a tool, which can be used to predict the behavior of a number of photopolymers subject to a range of physical conditions. In this paper, we explore the most recent developments made to the Non-local Photo-polymerization Driven Diffusion model, and illustrate some of the useful trends, which the model predicts and then analyze their implications on photopolymer improvement.Keywords: Holography, holographic recording material, photopolymer, inhibition. Contact Author: mgleeson@cs.nuim.ie and john.sheridan@ucd.ie INTRODUCTIONExtensive research and development of photopolymer materials and their photochemical kinetics [1-10] has been carried out in both academia and industry due to the growing interests in applications involving photopolymers [12][13][14][15][16][17][18][19].To maximise the potential of these materials, the provision of a physically comprehensive theoretical model of the effects occurring during and post-photo-polymerization is becoming ever more important. Such a model will enable potential trends in a material's performance to be recognized and optimised, [20][21][22][23][24][25][26][27][28][29][30]. An example of this is the two part paper published by Guo et al. [31,32] whereby chain transfer agents were added to reduce the effects of non-local polymer chain growth and hence improve the high density resolution of the photopolymer under examination.A recent publication by the authors [33] has presented a number of simulations of ratios of various key material components which offer possible methods to further improve photopolymer materials. This model's versatility has also been shown through its application to a number of other photopolymers, [34,35] including a material developed by Bayer MaterialScience (BMS), Germany. In this paper we extend the Non-local Photo-polymerization Driven Diffusion (NPDD) model used in the analysis provided in Ref.[33], to generate a more physically accurate representation of the processes occurring during photo-polymerisation. These extensions include; (i) time varying kinetic rates of reactions as a result of increased material viscosity (reduction in free volume), (ii) temporal and spatial variations in monomer and polymer diffusion due to increased material viscosity, (iii) full multicomponent analysis, inclusive of free space hole generation, (iv) independent monomer and crosslinker reactions and diffusion effects, (v) inter-diffusion effects between monomers and free space holes. It must also be clearly noted at this point, that the model includes; (a) non-steady state kinetics, (b) spatial and temporal non-local polymer chain growth, (c) time varying photon absorption, (d) temporal and spatial primary radical generation...