Sreekanth, Varma J; Dr.Jayalekshmi, S(Cochin University of Science and Technology, September , 2012)
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Abstract:
Light emitting polymers (LEP) have drawn considerable attention because of their numerous potential applications in the field of optoelectronic devices. Till date, a large number of organic molecules and polymers have been designed and devices fabricated based on these materials. Optoelectronic devices like polymer light emitting diodes (PLED) have attracted wide-spread research attention owing to their superior properties like flexibility, lower operational power, colour tunability and possibility of obtaining large area coatings. PLEDs can be utilized for the fabrication of flat panel displays and as replacements for incandescent lamps. The internal efficiency of the LEDs mainly depends on the electroluminescent efficiency of the emissive polymer such as quantum efficiency, luminance-voltage profile of LED and the balanced injection of electrons and holes. Poly (p-phenylenevinylene) (PPV) and regio-regular polythiophenes are interesting electro-active polymers which exhibit good electrical conductivity, electroluminescent activity and high film-forming properties. A combination of Red, Green and Blue emitting polymers is necessary for the generation of white light which can replace the high energy consuming incandescent lamps. Most of these polymers show very low solubility, stability and poor mechanical properties. Many of these light emitting polymers are based on conjugated extended chains of alternating phenyl and vinyl units. The intra-chain or inter-chain interactions within these polymer chains can change the emitted colour. Therefore an effective way of synthesizing polymers with reduced π-stacking, high solubility, high thermal stability and high light-emitting efficiency is still a challenge for chemists. New copolymers have to be effectively designed so as to solve these issues. Hence, in the present work, the suitability of a few novel copolymers with very high thermal stability, excellent solubility, intense light emission (blue, cyan and green) and high glass transition temperatures have been investigated to be used as emissive layers for polymer light emitting diodes.
Description:
Division for Research in Advanced Materials
Department of Physics, Cochin University of Science and Technology
Sreevalsa, V G; Dr.Jayalekshmi, S(Cochin University Of Science And Technology, November , 2012)
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Abstract:
Organic crystals possess extremely large optical nonlinearity compared
to inorganic crystals. Also organic compounds have the amenability for
synthesis and scope for introducing desirable characteristics by inclusions. A
wide variety of organic materials having electron donor and acceptor groups,
generate high order of nonlinearity. In the present work, a new nonlinear optical crystal, L-citrulline oxalate (LCO) based on the aminoacid L-citrulline was grown using slow evaporation technique. Structural characterization was carried out by single crystal XRD. It crystallizes in the noncentrosymmetric, orthorhombic structure with space group P21 P21 P21. Functional groups present in the sample were identified by Fourier transform infra red (FTIR) and FT-Raman spectral analysis. On studying the FTIR and Raman spectra of the precursors L-citrulline and oxalic acid, used for growing L-citrulline oxalate crystal, it is found that the
significant peaks of the precursors are present in the spectra of the L-citrulline
oxalate crystal . This observation along with the presence of NH3
+ group in the spectra of L-citrulline oxalate, confirms the formation of the charge
transfer complex
Description:
Department of Physics, Cochin University of Science and Technology
Jeeju, P P; Dr.Jayalekshmi, S(Cochin University of Science and Technology, June , 2012)
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Abstract:
The present work deals with investigations on some technologically important polymer nanocomposite films and semi crystalline polypyrrole films.The work presented in the thesis deals with the realization of novel polymer nanocomposites with enhanced functionalities and prospects of applications in the fields related to nanophotonics. The development of inorganic/polymer nanocomposites is a rapidly expanding multidisciplinary research area with profound industrial applications. The incorporation of suitable inorganic nanoparticles can endow the resulting nanocomposites with excellent electrical, optical and mechanical properties.
The first chapter gives a general introduction to nanotechnology, nanocomposites and conducting
polymers. It also emphasizes the significance of ZnO among other semiconductor materials, which forms the inorganic filler in the polymer nanocomposites of the present study. This chapter also gives general ideas on the properties and applications of conducting polymers with special reference to polypyrrole. The objectives of the present investigations are also clearly addressed in this chapter.
The second chapter deals with the theoretical aspects and details of all the experimental techniques used in the present work for the synthesis of polymer nanocomposites and polypyrrole samples and their various characterizations. Chapter 3 is based on the preparation and properties of ZnO/Polystyrene nanocomposite film samples. The optical properties of these nanocomoposite films are discussed in detail.Chapter 4 deals with the detailed investigations on the dependence of the optical properties of ZnO/PS nanocomposite films on the size of the nanostructured ZnO filler material. The excellent UV shielding properties of these nanocomposite films form the highlight of this chapter. Chapter 5 gives a detailed analysis of the nonlinear optical properties of ZnO/PS nanocomposite films using Z scan technique. The effect of ZnO particle size in the composite films on the nonlinear properties is discussed. The present study involves two phases of research activities. In the first phase, the linear and nonlinear optical properties of ZnO/polymer nanocomposites are investigated in detail. The second phase of work is centered on the synthesis and related studies on highly crystalline polypyrrole films.
In the present study, nanosized ZnO is synthesized using wet chemical method at two different temperatures
Description:
Department of Physics,
Cochin University of Science and Technology,
Ahmed Yasir,Vakayil; Mohan Das,P N; Mohammed Yusuff, K K(Department of Applied Chemistry, 2001)
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Abstract:
Titania is a versatile metal oxide with multiple applications. Titania supported catalysts are reported to be much more active compared to conventional silica or alumina supported ones in some reactions. TiO2 (anatase) having high surface area, with better crystallinity and high onset temperature of rutilation can be prepared by thermal hydrolysis of titanyl sulfate solution under controlled conditions. Calcinations at 350oC for 6 hrs were necessary to crystallize anatase. Method of preparation and percentage of the loaded metal oxides have greater influence on surface area. Drastic decrease in surface area was observed upon rutilation. Rutilation started at different temperatures depending on the metal oxide and the method of preparation. TiO2 should be characterized with high surface area, phase purity and high onset temperature of rutilation.Which should be well above the optimum temperature of a designated reaction in which it is employed as a catalyst. Variation in physical properties, depending upon the method of preparation is greater in TiO2 supported catalysts. Methanation activity was found to be highly dependent on nickel concentration present on the surface of the pellets. The methanation activity is strongly influenced by support material. The rate and turn over frequency of methanation and toluene oxidation activity of these catalysts are also equally important from an industrial point of view.
Manikandan,R; Dr.Krishnamoorthy,A(Cochin University Of Science And Technology, October 24, 2013)
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Abstract:
In this thesis the queueing-inventory models considered are analyzed
as continuous time Markov chains in which we use the tools such as matrix
analytic methods. We obtain the steady-state distributions of various
queueing-inventory models in product form under the assumption that no
customer joins the system when the inventory level is zero. This is despite
the strong correlation between the number of customers joining the system
and the inventory level during lead time. The resulting quasi-birth-anddeath
(QBD) processes are solved explicitly by matrix geometric methods
Description:
Department of Mathematics
Cochin University of Science and Technology
Nirmala, Paul; Dr.Krishna Pillai, M G(Cochin University Of Science And Technology, December 2, 1981)
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Abstract:
The thesis is a report of the attempts made to
prepare semiconducting and dielectric thin films and to
study their electrical properties. It consists of (i)
studies on the preparation and electrical characteristics
of compound semiconductor thin films of silver sulphide
and ferric hydroxide, and (ii) investigations on the electrical
and dielectric properties of plasma polymerized
thin films of para-toluidine element
Description:
Department
of Physics,Cochin University Of Science And Technology
Matlrew, George; Dr.Anantharaman, M R(Cochin University of Science & Technology, February , 2004)
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Abstract:
Magnetism and magnetic materials have been an ever-attractive
subject area for engineers and scientists alike because of its versatility in
finding applications in useful devices. They find applications in a host of
devices ranging from rudimentary devices like loud speakers to sophisticated
gadgets like waveguides and Magnetic Random Access Memories (MRAM).The one and only material in the realm of magnetism that has been at the
centre stage of applications is ferrites and in that spinel ferrites received the
lions share as far as practical applications are concerned.It has been the endeavour of scientists and engineers to remove
obsolescence and improve upon the existing so as to save energy and
integrate in to various other systems. This has been the hallmark of material
scientists and this has led to new materials and new technologies.In the field of ferrites too there has been considerable interest to
devise new materials based on iron oxides and other compounds. This means
synthesising ultra fine particles and tuning its properties to device new
materials. There are various preparation techniques ranging from top- down
to bottom-up approaches. This includes synthesising at molecular level, self
assembling,gas based condensation. Iow temperature eo-precipitation, solgel
process and high energy ball milling. Among these methods sol-gel
process allows good control of the properties of ceramic materials. The
advantage of this method includes processing at low temperature. mixing at
the molecular level and fabrication of novel materials for various devices.Composites are materials. which combine the good qualities of one
or more components. They can be prepared in situ or by mechanical means
by the incorporation of fine particles in appropriate matrixes. The size of the
magnetic powders as well as the nature of matrix affect the processability
and other physical properties of the final product. These plastic/rubber
magnets can in turn be useful for various applications in different devices.
In applications involving ferrites at high frequencies, it is essential that the
material possesses an appropriate dielectric permittivity and suitable
magnetic permeability. This can be achieved by synthesizing rubber ferrite
composites (RFC's). RFCs are very useful materials for microwave
absorptions. Hence the synthesis of ferrites in the nanoregirne.investigations on their size effects on the structural, magnetic, and electrical
properties and the incorporation of these ferrites into polymer matrixes
assume significance.In the present study, nano particles of NiFe204, Li(!5Fe2S04 and
Col-e-O, are prepared by sol gel method. By appropriate heat treatments,
particles of different grain sizes are obtained. The structural, magnetic and
electrical measurements are evaluated as a function of grain size and
temperature. NiFel04 prepared in the ultrafine regime are then incorporated
in nitrile rubber matrix. The incorporation was carried out according to a
specific recipe and for various loadings of magnetic fillers. The cure
characteristics, magnetic properties, electrical properties and mechanical
properties of these elastomer blends are carried out. The electrical
permittivity of all the rubber samples in the X - band are also conducted.
Description:
Department of Physics,
Cochin University of Science & Technology
Mathew, George; Dr.Anantharaman, M R(Cochin University Of Science And Technology, February 16, 2004)
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Abstract:
In the present study, nano particles of NiFe3O4, I_.l()5Feg5O4 and
CoFegO4 are prepared by sol gel method. By appropriate heat treatments,
particles of different grain sizes are obtained. The structural, magnetic and
electrical measurements are evaluated as a function of grain size and
temperature. NiFe3O4 prepared in the ultrafine regime are then incorporated
in nitrile rubber matrix. The incorporation was carried out according to a
specific recipe and for various loadings of magnetic fillers. The cure
characteristics, magnetic properties, electrical properties and mechanical
properties of these elastomer blends are carried out. The electrical
permittivity of all the rubber samples in the X — band are also conducted
Description:
Department of Physics
Cochin University of Science & Technology
Sagar, S; Dr.Anantharaman, M R(Cochin University of Science & Technology, August , 2010)
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Abstract:
This thesis lays importance in the investigation on the multiferroic and
thermooelectric properties of selected representatives of low bandwidth and
intermediate band width manganites. The first candidate, Strontium doped Gd manganite, is prepared by wet solid state reaction method and the second
candidate, Na doped La manganite, by citrate gel method. In addition to the above
mentioned properties, magneto resistance and dielectric properties are
investigated. Using dielectric spectroscopic the dispersion parameters are
correlated to the relaxation mechanisms and an attempt is made to obtain the grain
and grain boundary contribution to the impedance of the sample through
impedance spectroscopy studies.
Description:
Department of Physics,
Cochin University of Science & Technolog
Palson,T I; Dr.Joy, George(Cochin University Of Science And Technology, February 16, 1987)
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Abstract:
The work reported in this thesis is the preparation,
and the structural, electrical and optical properties
of reactively evaporated lead sulphide and tin telluride
thin films. The three temperature method had been used
for the preparation of these semiconductor thin films.
In this preparation technique constituent elements are
evaporated from separate sources with the substrate kept
at a particular temperature. when one of the constituent
element is a gas near room temperature, the method is
often called reactive evaporation. It has been found for
many materials that a stoichiometric interval exists with
a limited range of flux and substrate temperature. Usually
this technique is used for the preparation of thin films of
high melting point compounds or of materials which decompose
during evaporation. Tin telluride and lead sulphide are
neither high melting point materials nor do they decompose
on melting. But even than reactive evaporation offers the
possibility of changing the ratios of the flux of the constituent
elements within a wide range and studying its
effect on the properties of the films
Description:
Department of Physics, Cochin
University of Science and Technology