Fabrication and characterisation of polymer optical fibers for smart sensing and optical amplification

The thesis presented the fabrication and characterisation of polymer optical fibers in their applications as optical amplifier and smart sensors.Optical polymers such as PMMA are found to be a very good host material due to their ability to incorporate very high concentration of optical gain media like fluorescent dyes and rare earth compounds. High power and high gain optical amplification in organic dye-doped polymer optical fibers is possible due to extremely large emission cross sections of oyes. Dye doped (Rhodamine 6G) optical fibers were fabricated by using indigenously developed polymer optical fiber drawing tower. Loss characterization of drawn dye doped fibers was carried out using side illumination technique. The advantage of the above technique is that it is a nondestructive method and can also be used for studying the uniformity in fiber diameter and doping. Sensitivity of the undoped polymer fibers to temperature and microbending were also studied in its application in smart sensors.Optical amplification studies using the dye doped polymer optical fibers were carried out and found that an amplification of l8dB could be achieved using a very short fiber of length lOcm. Studies were carried out in fibers with different dye concentrations and diameter and it was observed that gain stability was achieved at relatively high dye concentrations irrespective of the fiber diameter.Due to their large diameter, large numerical aperture, flexibility and geometrical versatility of polymer optical fibers it has a wide range of applications in the field of optical sensing. Just as in the case of conventional silica based fiber optic sensors, sensing techniques like evanescent wave, grating and other intensity modulation schemes can also be efficiently utilized in the case of POF based sensors. Since polymer optical fibers have very low Young's modulus when compared to glass fibers, it can be utilized for sensing mechanical stress and strain efficiently in comparison with its counterpart. Fiber optic sensors have proved themselves as efficient and reliable devices to sense various parameters like aging, crack formation, weathering in civil structures. A similar type of study was carried out to find the setting characteristics of cement paste used for constructing civil structures. It was found that the measurements made by using fiber optic sensors are far more superior than that carried out by conventional methods. More over,POF based sensors were found to have more sensitivity as well.

Geochemical, Sedimentological And Remote Sensing Studies Of Kayamkulam Estuary, South West Coast Of India- A Gis Approach

In this study, an attempt has been made to find the textural, geochemical, sedimentological characteristics of sediments and water phases of the kayamkulam estuary located in the Southwest coast of Kerala, besides the impact of gas based thermal power plant located at the northern part of the estuary. Estuaries are an important stage in the transport of the solid weathering product of the earth’s crust. These weathered products or sediments are complex mixtures of a number of solid phases that may include clays, silica, organic matter, metal oxides, carbonates, sulfides and a number of minerals. Studies on the aquatic systems revealed the fact that it posses severe ecological impairments due to heavy discharge of sediments from 44 rivers, the continued disposal of pollutants rich materials from industries, sewage channels, agricultural areas and retting yards

Effect of Substrate Temperature on the Structural and Luminescent Characteristics of RF-Magnetron-Sputtered ZnGa2O4:Dy3+ Thin Films

ZnGa2O4:Dy3+ phosphor thin films were deposited on quartz substrates by radio frequency rf magnetron sputtering and the effect of substrate temperature on its structural and luminescent properties was investigated. Polycrystalline film could be deposited even at room temperature. The crystalline behavior, Zn/Ga ratio, and surface morphology of the films were found to be highly sensitive to substrate temperature. Under UV illumination, the as-deposited films at and above 300°C gave white luminescence even without any postdeposition treatments. The photoluminescent PL emission can be attributed to the combined effect of multicolor emissions from the single luminescence center Dy3+ via host-sensitization. Maximum PL emission intensity was observed for the film deposited at 600°C, and the CIE chromaticity coordinates of the emission were determined to be x,y = 0.34, 0.31 .

Effect of curing temperature , fibre loading and bonding agent on the equilibrium swelling of isora-natural rubbercomposites

Isora fibre-reinforced natural rubber (NR) composites were cured at 80, 100, 120 and 150°C using a low temperature curing accelerator system. Composites were also prepared using a conventional accelerator system and cured at 150°C. The swelling behavior of these composites at varying fibre loadings was studied in toluene and hexane. Results show that the uptake of solvent and volume fraction of rubber due to swelling was lower for the low temperature cured vulcanizates which is an indication of the better fibre/rubber adhesion. The uptake of aromatic solvent was higher than that of aliphatic solvent, for all the composites. As the fibre content increased, the solvent uptake decreased, due to the superior solvent resistance of the fibre and good fibre-rubber interactions. The bonding agent improved the swelling resistance of the composites due to the strong interfacial adhesion. Due to the improved adhesion between the fibre and rubber, the ratio of the change in volume fraction of rubber due to swelling to the volume fraction of rubber in the dry sample (V,) was found to decrease in the presence of bonding agent. At a fixed fibre loading, the alkali treated fibre composite showed a lower percentage swelling than untreated one for both systems showing superior rubber-fibre interactions.

A Novel Accelerator Combination for the Low Temperature Curing of Silica-Filled NBR Compounds

Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. The effect of these xanthates in combination with zinc diethyldithiocarbamate (ZDC) on the vulcanization of silica-filled NBR compounds has been studied at different temperatures. The cure times of these compounds were compared with that of NBR compounds containing tetramethylthiuram disulphide/dibenzthiazyl disulphide. The rubber compounds with the xanthates and ZDC were cured at various temperatures from 60 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, compression set, abrasion resistance, flex resistance, heat buildup, etc. were evaluated. The properties showed that zinc salt of xanthate/ZDC combination has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Low Temperature Curing of NBR for Property Improvement

Zinc salts of ethyl, isopropyl, and butyl xanthates are prepared in the laboratory, and the effect of these xanthates with zinc diethyl dithiocarbamate (ZDC) on the vulcanization of HAF-filled nitrile butadiene rubber (NBR) compounds has been studied at different temperatures. The cure times of these compounds have been compared with that of NBR compounds containing TMTD/MBTS. The rubber compounds with the three xanthate accelerators and ZDC are cured at various temperatures from 60 to 150°C. The sheets are molded and properties such as tensile strength, tear strength, cross-link density, elongation at break, compression set, abrasion resistance, flex resistance, etc. have been evaluated. The properties show that zinc salt of the xanthate/ZDC accelerator system has a positive synergistic effect on the cure rate and mechanical properties of NBR compounds.

Development of Polybutadiene (BR)-Polyethylene (LDPE) Blend Based Microcellular Soles for Low-Temperature Applications

Microcellular (MC) soles based on polybutadiene (BR) and low-density polyethylene (LDPE) blends for low-temperature applications were developed. A part of BR in BR-LDPE blend was replaced by natural rubber (NR) for property improvement. The BR-NR-LDPE blend-based MC sole shows good technical properties. Sulphur curing and DCP curing were tried in BR-LDPE and NR-BR-LDPE blends. Study shows that sulphur-cured MC sheets possess better technical properties than DCPcured MC sheets. 90/10 BR-LDPE and 60/30/10 BR-NR-LDPE blend combinations are found to be suitable for low-temperature applications.

Xanthate Accelerators for Low Temperature Curing of Natural Rubber

ABSTRACT: Zinc salts of ethyl, isopropyl, and butyl xanthates were prepared in the laboratory. They were purified by reprecipitation and were characterized by IR, NMR, and thermogravimetric analysis techniques. The melting points were also determined. The rubber compounds with different xanthate accelerators were cured at temperatures from 30 to 150°C. The sheets were molded and properties such as tensile strength, tear strength, crosslink density, elongation at break, and modulus at 300% elongation were evaluated. The properties showed that all three xanthate accelerators are effective for room temperature curing.

Temperature Stable Low Loss Ceramic Dielectrics in (1-x)ZnAI2O4-xTiO2 System for Microwave Substrate Applications

The microwave dielectric properties of ZnAl2O4 spinels were investigated and their properties were tailored by adding different mole fractions of Ti02. The samples were synthesized using the mixed oxide rout.e. The phase purity and crystal structure were identified using X-ray diffraction technique. The sintered specimens were characterized in the microwave frequency range (3-13 GHz). The ZnA12O4 ceramics exhibited interesting dielectric properties (dielectric constant (e,.) = 8.5, unloaded quality factor (Q.) = 4590 at 12.27 GHz and temperature coefficient of resonant frequency (Tf) = -79 ppm/°C). Addition of Ti02 into the spinel improved its properties and the Tf approached zero for 0.83ZnAl2O4- 0.17TiO2• This temperature compensated composition has excellent microwave dielectric properties (Cr _ 12.67, Q, = 9950 at 10.075 GHz) which can be exploited for microwave substrate applications

Phase transitions in lithium ammonium sulfate below room temperature: An ultrasonic study

A detailed ultrasonic study of the elastic properties of lithium ammonium sulfate ~LiNH4SO4! or LAS has been carried out below room temperature. The elastic constants of LAS at room temperature are reported. The discrepancy present in earlier elastic constant data associated with the different choice of axes for this orthorhombic system are clarified. The results of the temperature variation study down to 220 K confirm the ferroelastic phase transition at 285 K and establish a thermal hysteresis of about 2.5 K between the cooling and heating cycles. Results of the investigation on the suspected weak phase transition at 256 K suggest that this transition occurs at 242 K on cooling and at 256 K on heating, thus having a thermal hysteresis of about 14 K. However, since the observed elastic anomaly for this transition is very small, the nature of this transition still remains unclear