Fabrication and Characterization of Dye Sensitized Polymer Films for Holographic Applications

Holographic technology is at the dawn of quick evolution in various new areas including holographic data storage, holographic optical elements, artificial intelligence, optical interconnects, optical correlators, commerce, medical practice, holographic weapon sight, night vision goggles and games etc. One of the major obstacles for the success of holographic technology to a large extent is the lack of suitable recording medium. Compared with other holographic materials such as dichromated gelatin and silver halide emulsions, photopolymers have the great advantage of recording and reading holograms in real time and the spectral sensitivity could be easily shifted to the type of recording laser used by simply changing the sensitizing dye. Also these materials possess characteristics such as good light sensitivity, real time image development, large dynamic range, good optical properties, format flexibility, and low cost. This thesis describes the attempts made to fabricate highly economic photopolymer films for various holographic applications. In the present work, Poly (vinyl alcohol) (PVA) and poly (vinyl chloride) (PVC) are selected as the host polymer matrices and methylene blue (MB) is used as the photosensitizing dye. The films were fabricated using gravity settling method. No chemical treatment or pre/post exposures were applied to the films. As the outcome of the work, photopolymer films with more than 70% efficiency, a permanent recording material which required no fixing process, a reusable recording material etc. were fabricated.

Spectral and statistical characteristics of shoaling waves of Alleppey West coast of India

Some investigations on the spectral and statistical characteristics of deep water waves are available for Indian waters. But practically no systematic investigation on the shallow water wave spectral and probabilistic characteristics is made for any part of the Indian coast except for a few restricted studies. Hence a comprehensive study of the shallow water wave climate and their spectral and statistical characteristics for a location (Alleppey) along the southwest coast of India is undertaken based on recorded data. The results of the investigation are presented in this thesis.The thesis comprises of seven chapters

Tailoring Magnetic, Mechanical and Dielectric Properties of Magnetorheological Elastomers based on Natural Rubber and Iron by Magnetic Field Assisted Curing for Possible Applications

If magnetism is universal in nature, magnetic materials are ubiquitous. A life without magnetism is unthinkable and a day without the influence of a magnetic material is unimaginable. They find innumerable applications in the form of many passive and active devices namely, compass, electric motor, generator, microphone, loud speaker, maglev train, magnetic resonance imaging, data recording and reading, hadron collider etc. The list is endless. Such is the influence of magnetism and magnetic materials in ones day to day life. With the advent of nanoscience and nanotechnology, along with the emergence of new areas/fields such as spintronics, multiferroics and magnetic refrigeration, the importance of magnetism is ever increasing and attracting the attention of researchers worldwide. The search for a fluid which exhibits magnetism has been on for quite some time. However nature has not bestowed us with a magnetic fluid and hence it has been the dream of many researchers to synthesize a magnetic fluid which is thought to revolutionize many applications based on magnetism. The discovery of a magnetic fluid by Jacob Rabinow in the year 1952 paved the way for a new branch of Physics/Engineering which later became magnetic fluids. This gave birth to a new class of material called magnetorheological materials. Magnetorheological materials are considered superior to electrorheological materials in that magnetorheology is a contactless operation and often inexpensive.Most of the studies in the past on magnetorheological materials were based on magnetic fluids. Recently the focus has been on the solid state analogue of magnetic fluids which are called Magnetorheological Elastomers (MREs). The very word magnetorheological elastomer implies that the rheological properties of these materials can be altered by the influence of an external applied magnetic field and this process is reversible. If the application of an external magnetic field modifies the viscosity of a magnetic fluid, the effect of external magnetic stimuli on a magnetorheological elastomer is in the modification of its stiffness. They are reversible too. Magnetorheological materials exhibit variable stiffness and find applications in adaptive structures of aerospace, automotive civil and electrical engineering applications. The major advantage of MRE is that the particles are not able to settle with time and hence there is no need of a vessel to hold it. The possibility of hazardous waste leakage is no more with a solid MRE. Moreover, the particles in a solid MRE will not affect the performance and durability of the equipment. Usually MR solids work only in the pre yield region while MR fluids, typically work in the post yield state. The application of an external magnetic field modifies the stiffness constant, shear modulus and loss modulus which are complex quantities. In viscoelastic materials a part of the input energy is stored and released during each cycle and a part is dissipated as heat. The storage modulus G′ represents the capacity of the material to store energy of deformation, which contribute to material stiffness. The loss modulusG′′ represents the ability of the material to dissipate the energy of deformation. Such materials can find applications in the form of adaptive vibration absorbers (ATVAs), stiffness tunable mounts and variable impedance surfaces. MREs are an important material for automobile giants and became the focus of this research for eventual automatic vibration control, sound isolation, brakes, clutches and suspension systems

Enhancement of Diffraction Efficiency and Storage Life of Poly (Vinyl Chloride) Based Optical Recording Medium with the Incorporation of an Electron Donor

The differaction efficiency,sensitivity and storage life of Methylene Blue sencitized poly (vinyl chloride) film was improved by the addition of an electron donor in the matrix. The addition of pyridine enhanced the diffraction efficiency by two times and storage life of the gratings was increased to 2-3 days.

Fabrication and Characterization of Methylene-Blue-Doped Polyvinyl Alcohol–Polyacrylicacid Blend for Holographic Recording

A methylene-blue-sensitized polymer blend of polyvinyl alcohol and polyacrylic acid is fabricated and tested for holographic recording. It was found to have good characteristics such as high sensitivity, storage stability, ease of fabrication, and environmental stability. Optimization of the ratio of polyvinyl alcohol polyacrylic acid, the sensitizer concentration, pH, energy, diffraction efficiency measurements, etc., have been done. pH is found to have a great influence on the recovery of the dye in this matrix. The results of experimental investigations into the properties of this new material are reported.

Reusable Recording Medium Based on MBPVA and Vinyl Acetate

A new photopolymerizable recording media is introduced based on poly (vinyl alcohol) and vinyl acetate sensitized with methylene blue. It is observed that this MBPVA/VAc system can be reused a number of times without significant decrease in diffraction efficiency. The PVA-VAc ratio was optimized at 2:1. Diffraction efficiency of 6.3% was obtained without any fixing at a dye concentration of 9.3 10 4 mol/l at an exposure of 750 mJ/cm2. The material is attractive on account of its reusability.

Enhancement of Diffraction Efficiency and Storage Life of Poly (Vinyl Chloride) Based Optical Recording Medium with the Incorporation of an Electron Donor

The differaction efficiency,sensitivity and storage life of Methylene blue sensitized poly(vinyl chloride) film was improved by the addition of an electron donor in the matrix. The addition of pyridine enhanced the diffraction efficiency by two times and storage life of the gratings was increased to 2-3 days.

Fabrication and Characterization of Methylene-Blue-Doped Polyvinyl Alcohol–Polyacrylic Acid Blend for Holographic Recording

A methylene-blue-sensitized polymer blend of polyvinyl alcohol and polyacrylic acid is fabricated and tested for holographic recording. It was found to have good characteristics such as high sensitivity, storage stability, ease of fabrication, and environmental stability. Optimization of the ratio of polyvinyl alcohol polyacrylic acid, the sensitizer concentration, pH, energy, diffraction efficiency measurements, etc., have been done. pH is found to have a great influence on the recovery of the dye in this matrix. The results of experimental investigations into the properties of this new material are reported.

Reusable Recording Medium Based on MBPVA and vinyl Acetate

A new photopolymerizable recording media is introduced based on poly (vinyl alcohol) and vinyl acetate sensitized with methylene blue. It is observed that this MBPVA/VAc system can be reused a number of times without significant decrease in diffraction . The PVA-VAc ratio was optimized at 2:1. Diffraction efficiency of 6.3% was obtained without any fixing at a dye concentration of 9.3 10 4 mol/l at an exposure of 750 mJ/cm2. The material is attractive on account of its reusability.

Reusable recording medium based on MBPVA and vinyl acetate

A new photopolymerizable recording media is introduced based on poly (vinyl alcohol) and vinyl acetate sensitized with methylene blue. It is observed that this MBPVA/VAc system can be reused a number of times without significant decrease in diffraction efficiency. The PVA-VAc ratio was optimized at 2:1. Diffraction efcienc4y of 6.3% was obtained without any fixing at a dye concentration of 9.3 x 10- mol/l at an exposure of 750mJ/cm2. The material is attractive on account of its reusability.

Reusable Recording Medium Based on MBPVA and Vinyl Acetate

A new photopolymerizable recording media is introduced based on poly (vinyl alcohol) and vinyl acetate sensitized with methylene blue. It is observed that this MBPVA/VAc system can be reused a number of times without significant decrease in diffraction efficiency. The PVA-VAc ratio was optimized at 2:1. Diffraction efcienc4y of 6.3% was obtained without any fixing at a dye concentration of 9.3 x 10- mol/l at an exposure of 750mJ/cm2. The material is attractive on account of its reusability.

Reusable Recording Medium based on MBPVA and Vinyl Acetate

A new photopolymerizable recording media is introduced based on poly (vinyl alcohol) and vinyl acetate sensitized with methylene blue. It is observed that this MBPVA/VAc system can be reused a number of times without significant decrease in diffraction efficiency. The PVA-VAc ratio was optimized at 2:1. Diffraction efcienc4y of 6.3% was obtained without any fixing at a dye concentration of 9.3 x 10- mol/l at an exposure of 750mJ/cm2. The material is attractive on account of its reusability.

Preparation and characterisation of "Y-Fe203 as tape recording material

Optimum conditions for the preparation of tape recording quality Y-Fe20 s by the thermal decomposition of ferrous oxalate dihydrate have been established. Formation of the intermediate F%O~ which is most important in forming Y-FezO 3 takes place only in the presence of water vapour. Various stages of decomposition have been characterised by DTA, TG, DTG, and x-ray powder diffraction. The method for the preparation of acicular "Y-Fe208 that matches very well with the commercial tape recording material has been developed