Now showing 1 - 8 of 8
  • Publication
    Nonlocal photopolymerization kinetics including multiple termination mechanisms and dark reactions. Part II. Experimental validation
    (Optical Society of America, 2009-08-19) ; ; ;
    In the first of this series of papers [J. Opt. Soc. Am. B 26, 1736 (2009)], a new kinetic model, which includes most of the major photochemical and nonlocal photopolymerization driven diffusion effects, was proposed. Predictions made using the model were presented, and the numerical convergence of these simulations were examined when retaining higher-concentration harmonics. The validity and generality of the model is examined by applying it to fit experimental data for two different types of photopolymer material appearing in the literature. The first of these photopolymer materials involves an acrylamide monomer in a polyvinylalcohol matrix. The second is a more complex photopolymer in an epoxy resin matrix. Using the new model, key material parameters are extracted by numerically fitting experimentally obtained diffraction efficiency growth curves. The growth curves used include data captured both during exposure and post-exposure, allowing examination and analysis of "dark reactions".
      567Scopus© Citations 77
  • Publication
    Improvement of the spatial frequency response of photopolymer materials by modifying polymer chain length
    One of the key predictions of the nonlocal photopolymerization driven diffusion (NPDD) model is that a reduction in the extent of the nonlocal effects within a material will improve the high spatial frequency response. The NPDD model is generalized to more accurately model material absorbtivity. By eliminating the necessity for the steady-state approximation to describe the rate of change of monomer radical concentration, a more accurate physical representation of the initial transient behavior, at the start of grating growth, is achieved, which includes the effects of oxygen-based inhibition. The spatial frequency response of an acrylamide/polyvinylalcohol-based photopolymer is then improved through the addition of a chain transfer agent (CTA), sodium formate. Using the NPDD model demonstrates that the CTA has the effect of decreasing the average length of the polyacrylamide (PA) chains formed, thus reducing the nonlocal response parameter, σ. Further independent confirmation of the resulting reduction in the PA average molecular weight is provided using a diffusion-based holographic technique
      511Scopus© Citations 81
  • Publication
    Photoinitiation study of Irgacure 784 in an epoxy resin photopolymer
    (American Institute of Physics (AIP), 2010-03-10) ; ; ;
    A deeper understanding of the processes, which occur during free radical photopolymerization, is necessary in order to develop a fully comprehensive model, which represents their behavior during exposure. One of these processes is photoinitiation, whereby a photon is absorbed by a photosensitizer producing free radicals, which can initiate polymerization. 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 photosensitizer, in an epoxy resin matrix, is presented. We report our experimental results and present a theoretical model to predict the physically observed behavior.
      1420Scopus© Citations 56
  • Publication
    Examination of the photoinitiation processes in photopolymer materials
    (American Institute of Physics, 2008-09) ; ; ;
    Holographic data storage requires multiple sequential short exposures. However, the complete exposure schedule may not necessarily occur over a short time interval. Therefore, knowledge of the temporally varying absorptive effects of photopolymer materials becomes an important factor. In this paper, the time varying absorptive effects of an acrylamide/polyvinylalcohol photopolymer material are examined. These effects are divided into three main photochemical processes, which following identification, are theoretically and experimentally examined. These processes are (i) photon absorption, (ii) photosensitizer recovery, and (iii) photosensitizer bleaching.
      635Scopus© Citations 42
  • Publication
    Analysis of the photo-absorptive behavior of two different photosensitizers in a photopolymer material
    (Optical Society of America, 2009-03-01) ; ;
    Photopolymer materials are practical materials for use as holographic recording media. To further develop such materials, a deeper understanding of the photochemical mechanisms present during the formation of holographic gratings in these materials has become ever more crucial. This is especially true of the photoinitiation process, which has already received much attention in the literature. Typically the absorption mechanism varies with exposure time. This has been previously investigated in association with several effects taking place during recording. Since holographic data storage requires multiple sequential short exposures, it is necessary to verify the temporal change in photosensitizer concentration. Postexposure effects have also been discussed in the literature, however, such studies do not include effects such as photosensitizer recovery and bleaching. We report on experimental results and theoretical analysis of the recovery and bleaching mechanisms, which arise during exposure and postexposure for two different types of photosensitizers, methylene blue and erythrosine B in a polyvinylalcohol–acrylamide based photopolymer material.
      420Scopus© Citations 41
  • Publication
    Modeling the photochemical effects present during holographic grating formation in photopolymer materials
    The development of a theoretical model of the processes present during the formation of a holographic grating in photopolymer materials is crucial in enabling further development of holographic applications. To achieve this, it is necessary to understand the photochemical and photophysical processes involved and to isolate their effects, enabling each to be modeled accurately. While photopolymer materials are practical materials for use as holographic recording media, understanding the recording mechanisms will allow their limitations for certain processes to be overcome. In this paper we report generalizations of the nonlocal polymer driven diffusion (NPDD) model to include the effects of photosensitive dye absorption and the inhibition effects.
      499Scopus© Citations 60
  • Publication
    Non-local photo-polymerization kinetics including multiple termination mechanisms and dark reactions : part III. Primary radical generation and inhibition
    (Optical Society of America, 2010-09-01) ; ; ;
    Photopolymers are playing an ever more important role in diverse areas of research such as holographic data storage, hybrid photonic circuits, and solitary waves. In each of these applications, the production of primary radicals is the driving force of the polymerization processes. Therefore an understanding of the production, removal, and scavenging processes of free radicals in a photopolymer system is crucial in determining a material’s response to a given exposure. One such scavenging process is inhibition. In this paper the non-local photo-polymerization driven diffusion model is extended to more accurately model the effects of (i) time varying primary radical production, (ii) the rate of removal of photosensitizer, and (iii) inhibition. The model is presented to specifically analyze the effects of inhibition, which occur most predominantly at the start of grating growth, and comparisons between theory and experiment are performed which quantify these effects.
      549Scopus© Citations 61
  • Publication
    Extended model of the photoinitiation mechanisms in photopolymer materials
    (American Institute of Physics, 2009-11) ; ; ;
    In order to further improve photopolymer materials for applications such as data storage, a deeper understanding of the photochemical mechanisms which are present during the formation of holographic gratings has become ever more crucial. This is especially true of the photoinitiation processes, since holographic data storage requires multiple sequential short exposures. Previously, models describing the temporal variation in the photosensitizer (dye)concentration as a function of exposure have been presented and applied to two different types of photosensitizer, i.e., Methylene Blue and Erythrosine B, in a polyvinyl alcohol/acrylamide based photopolymer. These models include the effects of photosensitizer recovery and bleaching under certain limiting conditions. In this paper, based on a detailed study of the photochemical reactions, the previous models are further developed to more physically represent these effects. This enables a more accurate description of the time varying dye absorption, recovery, and bleaching, and therefore of the generation of primary radicals in photopolymers containing such dyes.
      570Scopus© Citations 31