Template-Assisted Synthesis and Characterization of Passivated Nickel Nanoparticles

Potential applications of nickel nanoparticles demand the synthesis of self-protected nickel nanoparticles by different synthesis techniques. A novel and simple technique for the synthesis of self-protected nickel nanoparticles is realized by the inter-matrix synthesis of nickel nanoparticles by cation exchange reduction in two types of resins. Two different polymer templates namely strongly acidic cation exchange resins and weakly acidic cation exchange resins provided with cation exchange sites which can anchor metal cations by the ion exchange process are used. The nickel ions which are held at the cation exchange sites by ion fixation can be subsequently reduced to metal nanoparticles by using sodium borohydride as the reducing agent. The composites are cycled repeating the loading reduction cycle involved in the synthesis procedure. X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron microscopy, Energy Dispersive Spectrum, and Inductively Coupled Plasma Analysis are effectively utilized to investigate the different structural characteristics of the nanocomposites. The hysteresis loop parameters namely saturation magnetization and coercivity are measured using Vibrating Sample Magnetometer. The thermomagnetization study is also conducted to evaluate the Curie temperature values of the composites. The effect of cycling on the structural and magnetic characteristics of the two composites are dealt in detail. A comparison between the different characteristics of the two nanocomposites is also provided

Investigations on the cation induced liquid crystalline phases of high molecular weight DNA

Liquid Crystalline DNA is emerging as an active area of research, due to its potential applications in diverse fields, ranging from nanoelectronics to therapeutics. Since, counter ion neutralization is an essential requirement for the expression of LC DNA, and the present level of understanding on the LC phase behavior of high molecular weight DNA is inadequate, a thorough investigation is required to understand the nature and stability of these phases under the influence of various cationic species. The present study is, therefore mainly focused on a comparative investigation of the effect of metal ions of varying charge, size, hydration and binding modes on the LC phase behavior of high molecular weight DNA. The main objectives of the works are investigations on the induction and stabilization of LC phases of high molecular weight DNA by alkali metal ions, investigations on the induction and stabilization of LC phases of high molecular weight DNA by alkaline earth metal ions, effects of multivalent, transition and heavy metal ions on the LC phase behavior of high molecular weight DNA and investigations on spermine induced LC behavior of high molecular weight DNA in the presence of alkali and alkaline earth metal ions. The critical DNA concentration (CD) required for the expression of LC phases, phase transitions and their stability varied considerably when the binding site of the metal ions changed from phosphate groups to the nitrogenous bases of DNA, with Li+ giving the highest stability. Multiple LC phases with different textures, sometimes diffused and unstable or otherwise mainly distinct and clear, were observed on mixing metal ions with DNA solutions, which in turn depended on the charge, size, hydration factor, binding modes, concentration of the metal ions and time. Molecular modeling studies on binding of selected metal ions to DNA supported the experimental findings

Rheological Characteristics of Short Nylon -6 Fiber Reinforced Styrene Butadiene Rubber Containing Epoxy Resin as Bonding Agent

The rheological characteristics of short Nylon-6 fiber-reinforced Styrene Butadiene rubber (SBR) in the presence of epoxy resin-based bonding agent were studied with respect to the effect of shear rate, fiber concentration , and temperature on shear viscosity and die swell using a capillary rheonzeter. All the composites containing bonding agent showed a pseudoplastic nature, which decreased with increasing temperature. Shear viscosity was increased in the presence of fibers. The temperature sensitivity of the SBR matrices was reduced on introduction of fibers. The temperature sensitivity of the melts was found to be lower at higher shear rates. Die swell was reduced in the presence of fibers. Relative viscosity of the composites increased with shear rate. In the presence of epoxy resin bonding agent the temperature sensitivity of the mixes increased. Die swell was larger in the presence of bonding agent.

Studies on short Nylon-6 fiber - elastomer composites with epoxy resin as bonding agent

The thesis describes the development and evaluation of epoxy resin as interfacial bonding agent for short Nylon-6 fiber elastomer composites. Epoxy resin is well known for its adhesive property. The potential use of it as interfacial bonding agent in short fiber composite is not explored yet. Three rubbers viz., acrylonitrile butadiene rubber (NBR), Neoprene rubber (CR) and styrene butadiene rubber (SBR) were selected and different fiber loading were tried. The resin concentration was optimized for each fiber loading with respect to cure characteristics and mechanical properties. Rheological characteristics and thermal degradation of the composites containing different fiber loading and different resin concentrations were studied in detail to find the effect of epoxy resin bonding system. The mechanical properties were studied in detail. The short Nylon -6 fiber improved most of the mechanical properties of all the three rubbers. Tensile strength showed a dip at 10 phr fiber loading in the case of CR while it was continuously increased with fiber loading in the case of NBR and SBR. All the composites showed anisotropy in mechanical properties. The epoxy resin is an effective bonding agent for short Nylon -6 fiber reinforced NBR and CR composites. Epoxy resin improved tensile strength, abrasion resistance and modulus of these composites. SEM studies confirmed the improved bonding of fiber and matrix in the presence of epoxy bonding agent. Epoxy resin was not effective as bonding agent in the case of short Nylon fiber- SBR composite. From the rheological studies of the composites with and without bonding agent it was observed that all the composite exhibited pseudoplasticity, which decreased with temperature. At higher shear rates all the mixes showed plug flow. SEM pictures showed that maximum orientation of fibers occured at a shear rate, just before the onset of plug flow. The presence of fiber reduced the temperature sensitivity of the flow at a given shear rate. Die swell was reduced in the presence of fiber. Shear viscosity of the composite was increased in the presence of resin. Die swell was increased in the presence of epoxy resin for composites at all shear rates. The thermal degradation of NBR and SBR composites with and without bonding agent followed single step degradation pattern. Thermal stability of the composites was improved in the presence of bonding agent. The degradation of virgin elastomer and the composites followed first order kinetics.

Modification of Phenol Formaldehyde Resin for Improved Mechanical Properties

Phenolic resins suffer from the presence of microvoids on curing. This often leads to less than satisfactory properties in the cured resin. This disadvantage has limited the use of phenolic resins to some extent. This study is an attempt to improve the mechanical properties of the phenolic resol resins by chemical modification aimed at reducing the microvoid population. With this end in view various themoset resins synthesised under predetennined conditions have been employed for modifying phenolic resols. Such resins include unsaturated polyester, epoxy and epoxy novolac prepolymers. The results establish the effectiveness of these resins for improving the mechanical properties of phenolics. Experimental and analytical techniques used include FTIR, DMA, TGA, SEM and mechanical property evaluation. While most of the modifier resins employed give positive results the effect of adding UP is found to be surprising as well as impressive.

Modification of Unsaturated Polyester Resin by Polyurethane Prepolymers

Unsaturated polyester resins (UPRs) are extensively used by the fiber-reinforced plastic (FRPs) industry. These resins have the disadvantages of brittleness and poor resistance to crack propagation. In this study, UPRs were chemically modified by reactive blending with polyurethane prepolymers having terminal isocyanate groups. Hybrid networks were formed by copolymerisation of unsaturated polyesters with styrene and simultaneous reaction between terminal hydroxyl groups of unsaturated polyester and isocyanate groups of polyurethane prepolymer. The prepolymers were based on toluene diisocyanate (TDI) and each of hydroxy-terminated natural rubber (HTNR), hydroxy- terminated polybutadiene (HTPB), polyethylene glycol (PEG), and castor oil. Properties like tensile strength, toughness, impact resistance, and elongation-at-break of the modified UPRs show considerable improvement by this modification. The thermal stability of the copolymer is also marginally better

Epoxidized Phenolic Novolac: A Novel Modifier for Unsaturated Polyester Resin

Unsaturated polyester resins (UPRs) are used widely in the fiber-reinforced plastics (FRPs) industry. These resins have the disadvantages of brittleness and poor resistance to crack propagation. In this study, hybrid polymer networks (HPNs) based on UPR and epoxidized phenolic novolacs (EPNs) were prepared by reactive blending. A HPN is composed of a backbone polymer containing two types of reactive groups that can take part in crosslinking reactions via different mechanisms. EPNs were prepared by glycidylation of novolacs using epichlorohydrin. The novolacs had varying phenol: formaldehyde ratios. Blends of unsaturated polyester with EPN were then prepared. The physical properties of the cured blends were compared with those of the control resin. EPN shows good miscibility and compatibility with the resin and improves the toughness and impact resistance substantially. Considerable enhancement of tensile strength is also noticed at about 5% by weight of epoxidized novolac resin. TGA, DMA, and DSC were used to study the thermal properties of the toughened resin and the fracture behavior was studied using SEM. The blends are also found to have better thermal stability. Blending with EPN can be a useful and cost-effective technique for modification of UPR