Synthesis and Study of Photophysical and Metal Ion Binding Properties of a Few Novel Semisquaraine and Croconaine Dyes

Photosciences & Photonics, Chemical Sciences & Technology Division, National Institute for Interdisciplinary Science & Technology

Weld line behaviour of polymer blends with special reference to PP/HDPE, PP/PS and HDPE/LDPE blends

Department of Polymer Science and Rubber Technology, Cochin University of Science and Technology

Synthesis,Characterisation and Uses of Polymer-bound Antioxidants

Department of Polymer Science and Rubber Technology,Cochin University of Science and Technology

Polymer Nanocomposites: Crystallization, Reinforcement and Conductivity through SWNTs

The current research investigates the possibility of using single walled carbon nanotubes (SWNTs) as filler in polymers to impart several properties to the matrix polymer. SWNTs in a polymer matrix like poly(ethylene terephthalate) induce nucleation in its melt crystallization, provide effective reinforcement and impart electrical conductivity. We adopt a simple melt compounding technique for incorporating the nanotubes into the polymer matrix. For attaining a better dispersion of the filler, an ultrasound assisted dissolution-evaporation method has also been tried. The resulting enhancement in the materials properties indicates an improved disentanglement of the nanotube ropes, which in turn provides effective matrix-filler interaction. PET-SWNT nanocomposite fibers prepared through melt spinning followed by subsequent drawing are also found to have significantly higher mechanical propertiesas compared to pristine PET fiber.SWNTs also find applications in composites based on elastomers such as natural rubber as they can impart electrical conductivity with simultaneous improvement in the mechanical properties.

Investigations on some selected conducting polymers and polymer composites for possible optoelectronic applications

Department of Physics, Cochin University of Science and Technology

Influence of residual cations (Na+, K+ and Mg2+) in the alkylation activity of benzene with 1-octene over rare earth metal ion exchanged FAU–Y zeolite

The effect of residual cations in rare earth metal modified faujasite–Y zeolite has been monitored using magic angle spinning NMR spectral analysis and catalytic activity studies. The second metal ions being used are Na+, K+ and Mg+. From a comparison of the spectra of different samples, it is concluded that potassium and magnesium exchange causes a greater downfield shift in the 29Si NMR peaks. Also, lanthanum exchanged samples show migration behavior from large cages to small cages, which causes the redistribution of second counter cations. It is also observed that Mg2+ causes the most effective migration of lanthanum ions due to its greater charge. The prepared systems were effectively employed for the alkylation of benzene with 1-octene in the vapor phase. From the deactivation studies it is observed that the as-exchanged zeolites possess better stability towards reaction condition over the pure HFAU zeolite.

Preparation and Characterization of Magnetic and Non-magnetic Nanosized Spinel Oxides, Nickel Nanoparticles and Nickel-Polymer Nanocomposites

Department of Physics, Cochin University of Science and Technology

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.

A new metal ion doped panchromatic photopolymer for holographic applications

This thesis has discussed the development of a new metal ion doped panchromatic photopolymer for various holographic applications. High-quality panchromatic holographic recording material with high diffraction efficiency, high photosensitivity and high spatial resolution is one of the key factors for the successful recording of true colour holograms. The capability of the developed material for multicolour holography can be investigated.In the present work, multiplexing studies were carried out using He-Ne laser (632.8 nm). Multiplexing can be done using low wavelength lasers like Ar+ ion (488 nm) and frequency doubled Nd: YAG (532 nm) lasers, so as to increase the storage capacity. The photopolymer film studied had a thickness of only 130 Cm. Films with high thickness (~500 Cm) is highly essential for competitive holographic memories . Hence films with high thickness can be fabricated and efforts can be made to record more holograms or gratings in the material.In the present study, attempts were made to record data page in silver doped MBPVA/AA photopolymer film. Image of a checkerboard pattern was recorded in the film, which could be reconstructed with good image fidelity. Efforts can be made to determine the bit error rate (BER) which provides a quantitative measure of the image quality of the reconstructed image . Multiple holographic data pages can also be recorded in the material making use of different multiplexing techniques.Holographic optical elements (HOEs) are widely used in optical sensors, optical information processing, fibre optics, optical scanners and solar concentrators . The suitability of the developed film for recording holographic optical elements like lenses, beam splitters and filters can be studied.The suitability of a reflection hologram recorded in acrylamide based photopolymer for visual indication of environmental humidity is reported . Studies can be done to optimize the film composition for recording of reflection holograms.An improvement in the spatial resolution of PVA/acrylamide based photopolymer by using a low molecular-weight poly (vinyl alcohol) binder was recently reported . Effect of the molecular weight of the binder matrix on the holographic properties of the developed photopolymer system can be investigated.Incorporation of nanoparticles into photopolymer system is reported to enhance the resolution and improve the dimensional stability of the system . Hence efforts can be made to incorporate silver nanoparticles into the photopolymer and its influence on the holographic properties can be studied.This thesis was a small venture towards the realization of a big goal, a competent holographic recording material with excellent properties for practical holographic applications. As a result of the present research, we could successfully develop an efficient panchromatic photopolymer system and could demonstrate its suitability for recording transmission holograms and holographic data page. The developed photopolymer system is expected to have significant applications in the fields of true-color display holography, wavelength multiplexing holographic storage, and holographic optical elements. Highly concentrated and determined effort has yet to be put forth for this expectation to become a reality.

Design and fabrication of a photothermal spectrometer and investigations of multilayer thin films"

In this work we present the results of our attempt to build a compact photothermal spectrometer capable of both manual and automated mode of operation.The salient features of the system include the ability to analyse thin film, powder and polymer samples. The tool has been in use to investigate thermal, optical and transport properties. Binary and ternary semiconducting thin films were analysed for their thermal diffusivities. The system could perform thickness measurements nondestructively. Ion implanted semiconductors are widely studied for the effect of radiation induced defects. We could perform nondestructive imaging of defects using our spectrometer.The results reported in his thesis on the above in addition to studies on In2S3 and transparent conducting oxide ZnO have been achieved with this spectrometer. Various polymer samples have been easily analysed for their thermal diffusivities. The technique provided ease of analysis not achieved with conventional techniques like TGA and DSC. Industrial application of the tool has also been proved by analyzing defects of welded joints and adhesion of paints. Indigenization of the expensive lock-in-amplifier and automation has been the significant achievement in the course of this dissertation. We are on our way to prove the noise rejection capabilities of our PC LIA.

Thermal diffusivity of some polymer supported halogeno benzimidazole complexes of cobalt(II) and copper(II) - a photoacoustic study

The thermal diffusivities of some polystyrene supported Schiff complexes of Co(II) and Cu(II) were determined by the laser induced photoacoustic technique. The effect of metal as well as the halogen part on thermal diffusivity of polymer supported complexes was studied. The thermal diffusivity of Co complexes increases while it decreases in Cu complexes with Cl, Br and I substitutions, respectively.

Light amplification in dye doped polymer films

We report unusual spectral narrowing and laser emission from polymer thin films doped with Coumarin 540 dye. The laser emission from the polymer films is found to be highly dependent upon the excitation length of the medium. Even a short length of 1.75 mm of the dye doped film gave rise to laser emission with FWHM of 0.3 nm for a pump intensity of 825 kW cm−2. The partial reflections from the broad lateral surfaces of the free standing films provided the optical feedback for the laser emission. Occurrence of well-resolved equally spaced resonant modes confirmed the effect of a Fabry–Perot-like optical cavity between the film surfaces.

A comparative study of energy transfer in dye mixtures in monomer and polymer matrices under pulsed laser excitation

This study was conducted to identify the concentration dependence of the operating wavelengths and the relative intensities in which a dye mixture doped polymer optical fibre can operate. A comparative study of the radiative and Forster type energy transfer processes in Coumarin 540:Rhodamine 6G, Coumarin 540:Rhodamine B and Rhodamine 6G:Rhodamine B in methyl methacrylate (MMA) and poly(methyl methacrylate) (PMMA) was done by fabricating a series of dye mixture doped polymer rods which have two emission peaks with varying relative intensities. These rods can be used as preforms for the fabrication of polymer optical fibre amplifiers operating in the multi-wavelength regime. The 445 nm line from an Nd:YAG pumped optical parametric oscillator (OPO) was used as the excitation source for the first two dye pairs and a frequency doubled Nd:YAG laser emitting at 532 nm was used to excite the Rh 6G:Rh B pair. The fluorescence lifetimes of the donor molecule in pure form as well as in the mixtures were experimentally measured in both monomer and polymer matrices by time-correlated single photon counting technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was analysed. It was found that radiative energy transfer mechanisms are more efficient in all the three dye pairs in liquid and solid matrices.

Excitation wavelength dependence of energy transfer in dye mixture doped polymer optical fibre preforms

Dependence of energy transfer parameters on excitation wavelength has been investigated in poly (methyl methacrylate) (PMMA) optical fibre preforms doped with C 540:Rh B dye mixture by studying the fluorescence intensity and the lifetime variations. A fluorescence spectrophotometer was used to record the excitation spectra of the samples for the emission wavelengths 495 and 580 nm. The fluorescence emission from the polymer rods was studied at four specific excitation wavelengths viz; 445, 465, 488 and 532 nm. The fluorescence lifetime of the donor molecule was experimentally measured in polymer matrix by time correlated single photon counting technique. The energy transfer rate constants and transfer efficiencies were calculated and their dependence on the acceptor concentration was analysed for three excitation wavelengths. It was found that any change in the excitation wavelength leads to significant variations in the quenching characteristics, which in turn affect the calculated energy transfer parameters.

Determination of the laser-induced damage threshold of bulk polymer samples at 1.06 mu m using the pulsed photothermal deflection technique

A pulsed Nd-YAG laser beam is used to produce a transient refractive index gradient in air adjoining the plane surface of the sample material. This refractive index gradient is probed by a continuous He-Ne laser beam propagating parallel to the sample surface. The observed deflection signals produced by the probe beam exhibit drastic variations when the pump laser energy density crosses the damage threshold for the sample. The measurements are used to estimate the damage threshold for a few polymer samples. The present values are found to be in good agreement with those determined by other methods.