Dielectric and Conductivity Studies on Cobalt Phthalocyanine Tetramers

Electrically conductive organic and metalloorganic polymers are of great interest and they have applications in electronic, optical, photonic, photoelectric, electrochemical, and dielectric devices. Tetrameric cobalt phthalocyanine was prepared by conventional chemical method. The dielectric permittivity of the tetrameric cobalt phthalocyanine sample was evaluated from the observed capacitance values in the frequency range 100 KHz to 5 MHz and in the temperature range of 300 to 383°K. It is found that the system obeys the Maxwell Wagner relaxation of space charge phenomenon. Further, from the permittivity studies AC conductivity was evaluated. The values of AC conductivity and DC conductivity were compared. Activation energy was calculated. To understand the conduction mechanism Mott’s variable range hopping model was applied to the system. The T 1/4 behavior of the DC conductivity along with the values of Mott’s Temperature (T0), density of states at the Fermi energy N (EF), and range of hopping R and hopping energy W indicate that the transport of charge carriers are by three-dimensional variable range hopping

Cure Characteristics and Mechanical Properties of Rubber Ferrite Composites Based on Nano-Nickel Ferrites

Ultra fine nickel ferrite have been synthesized by the sol-gel method. By heat treating different portions of the prepared powder separately at different temperatures, nano-sized particles of nickel ferrite with varying particle sizes were obtained. These powders were characterised by the X-ray diffraction and then incorporated in the nitrile rubber matrix according to a specific recipe for various loadings. The cure characteristics and the mechanical properties of these rubber ferrite composites (RFCs) were evaluated. The effect of loading and the grain size of the filler on the cure characteristics and tensile properties were also evaluated. It is found that the grain size and porosity of the filler plays a vital role in determining the mechanical properties of the RFCs

Radiopacity and Chemical resistance of Elastomer-Barium sulphate nanocomposites with special reference to Natural Rubber, Ethylene Propylene Rubber and Isobutylene Isoprene Rubber

The Human race of our century is in gluttonous search for novel engineering products which led to a skyrocketed progress in research and fabrication of filled polymers. Recently, a big window has been opened up for speciality polymers especially elastomers with promising properties. Among the many reasons why rubbers are widely used in the process industries, three are considered as important. Firstly, rubbers operate in a variety of environments and possess usable ranges of deformity and durability and can be exploited through suitable and more or less conventional equipment design principles. Secondly, rubber is an eminently suitable construction material for protection against corrosion in the chemical plant and equipment against various corrosive chemicals as, acids and alkalies and if property tailored, can shield ionising radiations as X-rays and gamma rays in medical industry, with minimum maintenance lower down time, negligible corrosion and a preferred choice for aggressive corroding and ionising environment. Thirdly, rubber can readily and hastily, and at a relatively lower cost, be converted into serviceable products, having intricate shapes and dimensions. In a century’s gap, large employment of flexible polymer materials in the different segments of industry has stimulated the development of new materials with special properties, which paved its way to the synthesis of various nanoscale materials. At nano scale, one makes an entry into a world where multidisciplinary sciences meet and utilises the previously unapproached infinitesimal length scale, having dimension which measure upto one billionth of a meter, to create novel properties. The nano fillers augment the elastomers properties in an astonishing fashion due to their multifunctional nature and unprecedented properties have been exhibited by these polymer-nanocomposites just to beat the shortcomings of traditional micro composites. The current research aims to investigate the possibility of using synthesised nano barium sulphate for fabricating elastomer-based nanocomposites and thereby imparting several properties to the rubber. In this thesis, nano materials, their synthesis, structure, properties and applications are studied. The properties of barium sulphate like chemical resistance and radiopacity have been utilized in the present study and is imparted to the elastomers by preparing composites

Design and Synthesis of Donor-Acceptor Low Band Gap Copolymers for Photoconductive and Non-linear Optical Applications

The main focus of the present study was to develop ideal low band gap D-A copolymers for photoconducting and non-linear optical applications. This chapter summarizes the overall research work done. Designed copolymers were synthesized via direct arylation or Suzuki coupling reactions. Copolymers were characterized by theoretical and experimental methods. The suitability of these copolymers in photoconducting and optical limiting devices has been investigated.The results suggest that the copolymers investigated in the present study have a good non-linear optical response and are comparable to or even better than the D-A copolymers reported in the literature and hence could be chosen as ideal candidates with potential applications for non-linear optics. The results also show that the structures of the polymers have great impact on NLO properties. Copolymers studied here exhibits good optical limiting property at 532 nm wavelength due to two-photon absorption (TPA) process. The results revealed that the two copolymers, (P(EDOT-BTSe) and P(PH-TZ)) exhibited strong two-photon absorption and superior optical power limiting properties, which are much better than that of others.

New studies on the versatile roles of Polyaniline and its composites in polymer based optoelectronic and energy storage devices

From the early stages of the twentieth century, polyaniline (PANI), a well-known and extensively studied conducting polymer has captured the attention of scientific community owing to its interesting electrical and optical properties. Starting from its structural properties, to the currently pursued optical, electrical and electrochemical properties, extensive investigations on pure PANI and its composites are still much relevant to explore its potentialities to the maximum extent. The synthesis of highly crystalline PANI films with ordered structure and high electrical conductivity has not been pursued in depth yet. Recently, nanostructured PANI and the nanocomposites of PANI have attracted a great deal of research attention owing to the possibilities of applications in optical switching devices, optoelectronics and energy storage devices. The work presented in the thesis is centered around the realization of highly conducting and structurally ordered PANI and its composites for applications mainly in the areas of nonlinear optics and electrochemical energy storage. Out of the vast variety of application fields of PANI, these two areas are specifically selected for the present studies, because of the following observations. The non-linear optical properties and the energy storing properties of PANI depend quite sensitively on the extent of conjugation of the polymer structure, the type and concentration of the dopants added and the type and size of the nano particles selected for making the nanocomposites. The first phase of the work is devoted to the synthesis of highly ordered and conducting films of PANI doped with various dopants and the structural, morphological and electrical characterization followed by the synthesis of metal nanoparticles incorporated PANI samples and the detailed optical characterization in the linear and nonlinear regimes. The second phase of the work comprises the investigations on the prospects of PANI in realizing polymer based rechargeable lithium ion cells with the inherent structural flexibility of polymer systems and environmental safety and stability. Secondary battery systems have become an inevitable part of daily life. They can be found in most of the portable electronic gadgets and recently they have started powering automobiles, although the power generated is low. The efficient storage of electrical energy generated from solar cells is achieved by using suitable secondary battery systems. The development of rechargeable battery systems having excellent charge storage capacity, cyclability, environmental friendliness and flexibility has yet to be realized in practice. Rechargeable Li-ion cells employing cathode active materials like LiCoO2, LiMn2O4, LiFePO4 have got remarkable charge storage capacity with least charge leakage when not in use. However, material toxicity, chance of cell explosion and lack of effective cell recycling mechanism pose significant risk factors which are to be addressed seriously. These cells also lack flexibility in their design due to the structural characteristics of the electrode materials. Global research is directed towards identifying new class of electrode materials with less risk factors and better structural stability and flexibility. Polymer based electrode materials with inherent flexibility, stability and eco-friendliness can be a suitable choice. One of the prime drawbacks of polymer based cathode materials is the low electronic conductivity. Hence the real task with this class of materials is to get better electronic conductivity with good electrical storage capability. Electronic conductivity can be enhanced by using proper dopants. In the designing of rechargeable Li-ion cells with polymer based cathode active materials, the key issue is to identify the optimum lithiation of the polymer cathode which can ensure the highest electronic conductivity and specific charge capacity possible The development of conducting polymer based rechargeable Li-ion cells with high specific capacity and excellent cycling characteristics is a highly competitive area among research and development groups, worldwide. Polymer based rechargeable batteries are specifically attractive due to the environmentally benign nature and the possible constructional flexibility they offer. Among polymers having electrical transport properties suitable for rechargeable battery applications, polyaniline is the most favoured one due to its tunable electrical conducting properties and the availability of cost effective precursor materials for its synthesis. The performance of a battery depends significantly on the characteristics of its integral parts, the cathode, anode and the electrolyte, which in turn depend on the materials used. Many research groups are involved in developing new electrode and electrolyte materials to enhance the overall performance efficiency of the battery. Currently explored electrolytes for Li ion battery applications are in liquid or gel form, which makes well-defined sealing essential. The use of solid electrolytes eliminates the need for containment of liquid electrolytes, which will certainly simplify the cell design and improve the safety and durability. The other advantages of polymer electrolytes include dimensional stability, safety and the ability to prevent lithium dendrite formation. One of the ultimate aims of the present work is to realize all solid state, flexible and environment friendly Li-ion cells with high specific capacity and excellent cycling stability. Part of the present work is hence focused on identifying good polymer based solid electrolytes essential for realizing all solid state polymer based Li ion cells.The present work is an attempt to study the versatile roles of polyaniline in two different fields of technological applications like nonlinear optics and energy storage. Conducting form of doped PANI films with good extent of crystallinity have been realized using a level surface assisted casting method in addition to the generally employed technique of spin coating. Metal nanoparticles embedded PANI offers a rich source for nonlinear optical studies and hence gold and silver nanoparticles have been used for making the nanocomposites in bulk and thin film forms. These PANI nanocomposites are found to exhibit quite dominant third order optical non-linearity. The highlight of these studies is the observation of the interesting phenomenon of the switching between saturable absorption (SA) and reverse saturable absorption (RSA) in the films of Ag/PANI and Au/PANI nanocomposites, which offers prospects of applications in optical switching. The investigations on the energy storage prospects of PANI were carried out on Li enriched PANI which was used as the cathode active material for assembling rechargeable Li-ion cells. For Li enrichment or Li doping of PANI, n-Butyllithium (n-BuLi) in hexanes was used. The Li doping as well as the Li-ion cell assembling were carried out in an argon filled glove box. Coin cells were assembled with Li doped PANI with different doping concentrations, as the cathode, LiPF6 as the electrolyte and Li metal as the anode. These coin cells are found to show reasonably good specific capacity around 22mAh/g and excellent cycling stability and coulombic efficiency around 99%. To improve the specific capacity, composites of Li doped PANI with inorganic cathode active materials like LiFePO4 and LiMn2O4 were synthesized and coin cells were assembled as mentioned earlier to assess the electrochemical capability. The cells assembled using the composite cathodes are found to show significant enhancement in specific capacity to around 40mAh/g. One of the other interesting observations is the complete blocking of the adverse effects of Jahn-Teller distortion, when the composite cathode, PANI-LiMn2O4 is used for assembling the Li-ion cells. This distortion is generally observed, near room temperature, when LiMn2O4 is used as the cathode, which significantly reduces the cycling stability of the cells.

Association Behavior of Biotinylated and Non-Biotinylated PolyEthylene Oxide-b-Poly(2-(Diethylamino)Ethyl Methacrylate)

Biotinylated and non-biotinylated copolymers of ethylene oxide (EO) and 2-(diethylamino)ethyl methacrylate (DEAEMA) were synthesized by the atom transfer radical polymerization technique (ATRP). The chemical compositions of the copolymers as determined by NMR are represented by PEO₁₁₃PDEAEMA₇₀ and biotin-PEO₁₀₄PDEAEMA₉₃ respectively. The aggregation behavior of these polymers in aqueous solutions at different pHs and ionic strengths was studied using a combination of potentiometric titration, dynamic light scattering (DLS), static light scattering (SLS), and transmission electron microscopy (TEM). Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers form micelles at high pH with hydrodynamic radii (Rh) of about 19 and 23 nm, respectively. At low pH, the copolymers are dispersed as unimers in solution with Rh of about 6-7 nm. However, at a physiological salt concentration (cs) of about 0.16M NaCl and a pH of 7-8, the copolymers form large loosely packed Guassian chains, which were not present at the low cs of 0.001M NaCl. The critical micelle concentrations (CMC) and the cytotoxicity of the copolymers were investigated to determine a suitable polymer concentration range for future biological applications. Both PEO-b-PDEAEMA and biotin-PEO-b-PDEAEMA diblock copolymers possess identical CMC values of about 0.0023 mg/g, while the cytotoxicity test indicated that the copolymers are not toxic up to 0.05mg/g (> 83% cell survival at this concentration).

Synthesis, Optical properties and Applications of Water Soluble Conjugated PPPs for Biosensors

In recent years, application of fluorescent conjugated polymers to sense chemical and biological analytes has received much attention owing to its technological significance. Water soluble conjugated polymers are interesting towards the developing sensors for biomolecules. In this present contribution, we describe the syntheses and characterization of a series of water soluble conjugated polymers with sulfonic acid groups in the side chain. Such anionic conjugated polymers are designed to interact with biomolecules such as cytochrome-C. All polymers are water soluble and showed strong blue emission. Significant quenching of the fluorescence from our functionalized PPP was observed upon addition of viologen derivatives or cytochrome -C.

Analysis and Simulation of Transverse Random Fracture of Long Fibre Reinforced Composites

La present tesi proposa una metodología per a la simulació probabilística de la fallada de la matriu en materials compòsits reforçats amb fibres de carboni, basant-se en l'anàlisi de la distribució aleatòria de les fibres. En els primers capítols es revisa l'estat de l'art sobre modelització matemàtica de materials aleatoris, càlcul de propietats efectives i criteris de fallada transversal en materials compòsits. El primer pas en la metodologia proposada és la definició de la determinació del tamany mínim d'un Element de Volum Representatiu Estadístic (SRVE) . Aquesta determinació es du a terme analitzant el volum de fibra, les propietats elàstiques efectives, la condició de Hill, els estadístics de les components de tensió i defromació, la funció de densitat de probabilitat i les funcions estadístiques de distància entre fibres de models d'elements de la microestructura, de diferent tamany. Un cop s'ha determinat aquest tamany mínim, es comparen un model periòdic i un model aleatori, per constatar la magnitud de les diferències que s'hi observen. Es defineix, també, una metodologia per a l'anàlisi estadístic de la distribució de la fibra en el compòsit, a partir d'imatges digitals de la secció transversal. Aquest anàlisi s'aplica a quatre materials diferents. Finalment, es proposa un mètode computacional de dues escales per a simular la fallada transversal de làmines unidireccionals, que permet obtenir funcions de densitat de probabilitat per a les variables mecàniques. Es descriuen algunes aplicacions i possibilitats d'aquest mètode i es comparen els resultats obtinguts de la simulació amb valors experimentals.

Study of bond behaviour between FRP reinforcement and concrete

El uso de barras de materiales compuestos (FRP) se propone como una alternativa efectiva para las tradicionales estructuras de hormigón armadas con acero que sufren corrosión en ambientes agresivos. La aceptación de estos materiales en el mundo de la construcción está condicionada a la compresión de su comportamiento estructural. Este trabajo estudia el comportamiento adherente entre barras de FRP y hormigón mediante dos programas experimentales. El primero incluye la caracterización de la adherencia entre barras de FRP y hormigón mediante ensayos de pull-out y el segundo estudia el proceso de fisuración de tirantes de hormigón reforzados con barras de GFRP mediante ensayo a tracción directa. El trabajo se concluye con el desarrollo de un modelo numérico para la simulación del comportamiento de elementos de hormigón reforzado bajo cargas de tracción. La flexibilidad del modelo lo convierte en una herramienta flexible para la realización de un estudio paramétrico sobre las variables que influyen en el proceso de fisuración.

Linear viscoelasticity from molecular dynamics simulation of entangled polymers

The linear viscoelastic (LVE) spectrum is one of the primary fingerprints of polymer solutions and melts, carrying information about most relaxation processes in the system. Many single chain theories and models start with predicting the LVE spectrum to validate their assumptions. However, until now, no reliable linear stress relaxation data were available from simulations of multichain systems. In this work, we propose a new efficient way to calculate a wide variety of correlation functions and mean-square displacements during simulations without significant additional CPU cost. Using this method, we calculate stress−stress autocorrelation functions for a simple bead−spring model of polymer melt for a wide range of chain lengths, densities, temperatures, and chain stiffnesses. The obtained stress−stress autocorrelation functions were compared with the single chain slip−spring model in order to obtain entanglement related parameters, such as the plateau modulus or the molecular weight between entanglements. Then, the dependence of the plateau modulus on the packing length is discussed. We have also identified three different contributions to the stress relaxation:  bond length relaxation, colloidal and polymeric. Their dependence on the density and the temperature is demonstrated for short unentangled systems without inertia.

Hierarchical modeling of entangled polymers

We demonstrate that it is possible to link multi-chain molecular dynamics simulations with the tube model using a single chain slip-links model as a bridge. This hierarchical approach allows significant speed up of simulations, permitting us to span the time scales relevant for a comparison with the tube theory. Fitting the mean-square displacement of individual monomers in molecular dynamics simulations with the slip-spring model, we show that it is possible to predict the stress relaxation. Then, we analyze the stress relaxation from slip-spring simulations in the framework of the tube theory. In the absence of constraint release, we establish that the relaxation modulus can be decomposed as the sum of contributions from fast and longitudinal Rouse modes, and tube survival. Finally, we discuss some open questions regarding possible future directions that could be profitable in rendering the tube model quantitative, even for mildly entangled polymers