Polyvinyl Alcohol Acrylamide Research Articles

Analysis of the Imaging Characteristics of Holographic Waveguides Recorded in Photopolymers.

In this work, we study the imaging characteristics of an optical see-through display based on a holographic waveguide. To fabricate this device, two transmission holograms are recorded on a photopolymer material attached to a glass substrate. The role of the holograms is to couple the incident light between air and the glass substrate, accomplishing total internal reflection. The role of noise reflection gratings and shrinkage on the imaging characteristics of the device will be also explored. The holograms (slanted transmission gratings with a spatial frequency of 1690 lines/mm) were recorded on a polyvinyl alcohol acrylamide holographic polymer dispersed liquid crystal (HPDLC) material. We will show that sufficient refractive index modulation is achieved in the material, in order to obtain high diffraction efficiencies. We will demonstrate that the final device acts as an image formation system.

Holographic waveguides in photopolymers

The possibilities that offer the holographic optical elements for photovoltaic and "see through display" applications open new windows for holographic recording materials. In this sense, some specific characteristics are required for each particular application. Waveguides are one of the key elements for these applications. Photopolymers are one of the most competitive candidates for waveguide fabrication. In this work, we evaluate the performance of one example from each of three families of photopolymer material in fabrication of a 633nm waveguide. Firstly, polyvinyl alcohol acrylamide, PVA/AA, the second one, a nanoparticle-thiol-ene, NPC, and on the last place a penta/hexa-acrylate based polymer with dispersed nematic liquid crystal molecules, PDLC. We study the critical role of the material and in particular, spatial resolution for this application.

Optimization of Photopolymer Materials for the Fabrication of a Holographic Waveguide.

In this work, we present a method of manufacturing an optical see-through display based on a holographic waveguide with transmission holograms that couple the incident light between air and the glass substrate, accomplishing total internal reflection. The holograms (slanted transmission gratings with a spatial frequency of 1700 lines/mm) were recorded on a polyvinyl alcohol acrylamide (PVA/AA) photopolymer. We will also show that the addition of N,N′-methylene-bis-acrylamide (BMA) to the composition of the photopolymer allows the achievement of the index modulations necessary to obtain high diffraction efficiencies in non-slanted diffraction gratings of 1000 and 2200 lines/mm, and also in slanted gratings of 1700 lines/mm (which are the base of the optical system proposed).

Improvement on efficiencies of dilute alkaline water electrolyzer using membranes

Electrolysis of 0.50% (w/v) aqueous KOH solution with novel packed bed electrodes made of SS 316 solid cylindrical packing has been carried out using membranes with three different combinations, namely Poly vinyl alcohol-acrylamide (PVA-AAm), Poly vinyl alcohol-Acrylic acid (PVA-AAc) and Poly vinyl alcohol-Acrylic acid-acrylamide (PVA-AAc-AAm).For production of hydrogen, nearly 100% current efficiency and about 50% energy efficiency have been achieved by using PVA-AAc and PVA-AAc-AAm membranes. FTIR analyses of fresh and used membranes as well as AAS analyses of anolyte and catholyte confirm that membranes prevent transportation of Fe ions from anode to cathode resulting in better current and energy efficiencies for production of hydrogen and oxygen. PVA-AAm membrane has been found to be unsuitable as AAm reacts and decomposes to AAc during electrolysis in dilute KOH solution. The ratios of production rates of hydrogen to oxygen reach the steady state value of 2 in 2 h which confirms the consumption of oxygen by undesired reactions at initial stages.

Diffractive lenses recorded in absorbent photopolymers.

Photopolymers can be appealing materials for diffractive optical elements fabrication. In this paper, we present the recording of diffractive lenses in PVA/AA (Polyvinyl alcohol acrylamide) based photopolymers using a liquid crystal device as a master. In addition, we study the viability of using a diffusion model to simulate the lens formation in the material and to study the influence of the different parameters that govern the diffractive formation in photopolymers. Once we control the influence of each parameter, we can fit an optimum recording schedule to record each different diffractive optical element with the optimum focalization power.

Reflection mode holographic recording in methylene blue-sensitized polyvinyl alcohol acrylamide films

Photopolymer systems can produce good image quality holograms that does not require any post-processing and are environmentally stable with good diffraction efficiency. The present work reports the development of a methylene blue-sensitized polyvinyl alcohol acrylamide (MBPVA/AA) photopolymer system for recording white light reflection holograms. Reflection gratings were recorded in the photopolymer films with different concentrations of methylene blue (MB). Various parameters affecting the holographic properties of the samples were also studied. The holographic performance of the material is found to depend on its chemical composition and the recording parameters.

Humidity and temperature effect on properties of transmission gratings recorded in PVA/AA-based photopolymer layers

This paper explores the effects of humidity on gratings recorded in a polyvinylalcohol–acrylamide photopolymer medium. Investigation of the behaviour of transmission gratings exposed to high humidity is of significant interest for two reasons, firstly because the grating’s sensitivity to humidity can be exploited for the development of irreversible humidity indicators, secondly because too much sensitivity to humidity can limit the use of these materials in applications where an environmentally stable hologram is needed. In this paper we focus on the effect of high humidity on the properties of volume phase transmission gratings recorded in PVA/AA photopolymer layers in the temperature range 8–24 ° C. It has been found that although exposure to humidity changes the diffraction efficiency and Bragg angle of gratings, the effects are fully reversible if the temperatures are kept low. For example, when gratings were subjected to relative humidities of 80% and 90% at a temperature of 8 ° C the observed changes were fully reversible. However, irreversible changes in diffraction efficiency, thickness, refractive index modulation and Bragg angle were observed when the temperature during the humidity exposure was higher than 16 ° C. The magnitude of the irreversible changes depends strongly on the ambient temperature during the humidity exposure, the humidity level and also on the duration of the humidity exposure.

Comparison of peristrophic multiplexing and a combination of angular and peristrophic holographic multiplexing in a thick PVA/acrylamide photopolymer for data storage

Two different types of multiplexing are used to store 90 holograms at the same location in a polyvinyl alcoholacrylamide photopolymer material. In the first, the 90 holograms are stored using only peristrophic multiplexing, whereas in the second a combination of angular and peristrophic multiplexing is used. The results (diffraction efficiency and dynamic range, M#) obtained with these two multiplexing techniques are compared. With the first, the dynamic range was M# = 13 and with the second M# = 8. An exposure schedule method is used to calculate the exposure time necessary to store the holograms with a more uniform, higher diffraction efficiency.

First-harmonic diffusion-based model applied to a polyvinyl-alcohol–acrylamide-based photopolymer

The photopolymerization diffusion models give accurate comprehension of the mechanism of hologram formation inside photopolymer materials. Although several models have been proposed, these models share the common assumption that there is an interplay between the processes of monomer polymerization and monomer diffusion. Nevertheless, most of the studies to check the validity of the theoretical models have been done by using photopolymers of the DuPont™ type, or photopolymer materials with values of the monomer diffusion time similar to those of the DuPont material. We check the applicability of a modified diffusion-based model to a polyvinyl alcohol–acrylamide photopolymer. This material has the property of longer diffusion times for the monomer to travel from the unexposed to the exposed zones than in the case of other polymeric materials. Some interesting effects are observed and theoretically treated by using the modified first-harmonic diffusion-based model we propose.