Photopolymers

The hard research about the models to predict and understand the behaviour of photopolymers have as a results many interesting works for 2-dimensional cases. These studies permits obtain the mains parameters that governs the process in photopolymers with maximum thickness about 200 μm. Historically this materials, dry layers of photopolymers, have been used in many attractive devices and now a new application of this type of material is being developed: the application of photopolymers as holographic memories. The main characteristics of these layers of photopolymers are their high thickness (higher than 600 μm). In order to optimize this layers the original photopolymer composition has been changed, then a new parameters estimation has be done. In this work this study is made using PVA/Acrylamide photopolymer with layers around 800 μm of thick. The values of monomer and polymer diffusion are obtained and the values of polymerization rate constant and residual monomer are calculated too using and first harmonic diffusion constant. The validity of this model to study the layers with high thickness is evaluated, because this type of materials only a few percent of the initial light arrive to the depth zones of photopolymer.

Neural precursor cells (NPCs) are a renewable cell source that may be useful for neural cell transplant therapies. Their expansion and differentiation potential have traditionally been explored by culturing them on stiff tissue culture polystyrene. Here we describe advantages of an alternative culture system: bio-inert poly(ethylene glycol) (PEG) hydrogels. Specifically this work reports the effect that macromer weight percent has on the metabolic and apoptotic activity, proliferation, and cellular composition of a mixed population of neurons and multipotent NPCs grown both on 2D and within 3D PEG hydrogels. In 2D culture, hydrogel properties did not affect metabolic or apoptotic activity but did impact cell proliferation and composition leading to an increase in glial cell reactivity as stiffness increased. In 3D culture, low weight percent hydrogels led to greater metabolic activity and lower apoptotic activity with significant proliferation observed only in hydrogels that closely matched the stiffness of native brain tissue. PEG hydrogels therefore provide a versatile in vitro culture system that can be used to culture and expand a variety of neural and glial cell types simply by altering the material properties of the hydrogel. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2010.

The kinetics of photosensitive polymer holographic recording materials are examined assuming a material that exhibits nonideal kinetic behavior. Previously, a linear relationship between monomer concentration and polymerization was assumed when deriving the nonlocal polymer-driven diffusion (NPDD) model. This is consistent with ideal kinetic conditions in which chain termination is governed by a bimolecular process. However, these models have been reported to disagree with experimental results. In a limiting case of nonideal kinetics it is assumed that primary termination is dominant. In this case the NPDD model must be modified to incorporate a quadratic relationship between the monomer concentration and the polymerization rate. By use of a multiharmonic expansion method of solution the predictions of ideal (bimolecular or linear) and nonideal (primary or quadratic) kinetic models are compared. By using these models we carried out numerical fits to experimental growth curves of gratings recorded in an acrylamide-based cross-linked photopolymer system. Superior fits are achieved by use of the primary termination model. Physical parameters such as the diffusion constant are extracted and compared with results previously reported in the literature.

El conocimiento de las propiedades mecánicas de los materiales utilizados comúnmente para el registro de elementos ópticos difractivos es de gran importancia para predecir su comportamiento mecánico durante el procesado fotoquímico al que se les somete durante el grabado del patrón interferencial. Esto también proporcionará información sobre la estabilidad mecánica y térmica del holograma almacenado en estos materiales en los diferentes entornos en los que será aplicado definitivamente. Para evaluar cuantitativamente estas propiedades en un sistema fotopolimérico basado en acrilamidas se realizó un estudio sobre capas de polivinilalcohol (polímero soporte del sistema fotopolimérico). Las capas previamente depositadas sobre un sustrato de vidrio se sometieron a alto vacío y posteriormente a un cambio de temperatura. Las medidas en tiempo real de las variaciones de camino óptico sufridas por la capa se obtuvieron usando un sistema de medida interferométrico en alto vacío. Evaluation o...

Holographic recording is an effective approach for photopolymer surface patterning. It has been previously utilised in acrylamide-based photopolymers and a spatial frequency limit of 200 l/mm has been observed. We report the successful inscription of submicrometer resolution patterns. The spatial frequency response has been extended to 1550 l/mm by introduction of thermal post recording treatment. Initial results from the optical

We report on how polymer morphology is controlled through the self-trapping of transmitted optical beams in photoreactive polymer blends. Self-trapped optical beams, characterized by divergence-free propagation, drives the growth of a congruent arrangement of polymer filaments in the blends. With suitable component weight fractions and exposure intensity, binary phase morphologies form in precisely the same pattern as the beams' arrangement, thereby producing 2D structures in polymer blend volumes of large depth and area. Morphology evolution and the formation processes were observed by in situ microscopy. In situ confocal Raman measurements of polymer conversion and molecular weight increase along the filament regions reveal that polymerization undergoes autoacceleration, followed by the onset of mixing instability which leads to phase separation. These phenomena begin at the front end of the filament and propagate along its length over the depth of the blend. Control over morphology is discussed with respect to the competitive processes of phase separation and photo-cross-linking.