Academic literature on the topic 'Glass-Nanocomposites'

Metallic nanoparticles and nanostructures have spawned significant interest in a wide area of science. Nanoparticles in glass show unique linear and nonlinear optical properties due to surface plasmon resonances. These induce absorption and scattering of light around the resonance wavelength, which can be tuned by changing size, shape or spatial distribution of the nanoparticles. Metallic nanostructures show local field enhancement effects, which are used for example in surface enhanced Raman scattering. Their large surface area compared to bulk materials makes them interesting for applications in chemistry and life science. In this thesis the synthesis of two different types of silver-glass nanocomposites is investigated. Both materials are prepared from silver ion-exchanged glass, which is also prepared and characterised in house. The first type of nanocomposite is glass doped with silver nanoparticles. It is formed by annealing silver ion-exchanged glass at a temperature close to the transition point. This induces the reduction of silver to atoms and the agglomeration in nanoparticles with a diameter of less than 10nm, which are located in a layer beneath the glass surface, which has a thickness of tens of micrometres. These nanoparticles are responsible for a characteristic absorption band centred around 410nm due to plasmon resonances. The second nanocomposite, which was first produced in the course of this work, is called glass-silver composite. It is created by pulsed laser irradiation of silver ion-exchanged glass. It contains nanoparticles with a diameter of 100nm or more, which are distributed homogeneously in a dense single monolayer at the glass surface. This material shows a strong metal-like reflection of light. The location of nanoparticles at the surface makes it interesting for applications utilising the field enhancement effect of the nanoparticles, such as surface enhanced Raman scattering and enhancement of light conversion. Both nanocomposites and the ion-exchanged glass are characterised by optical microscopy, scanning electron microscopy and optical spectroscopy. The work is divided in four chapters, starting with an introduction in chapter 1. In chapter 2 the method of production of the silver ion-exchanged glass and the properties of the material are presented. Generation of nanoparticles inside the glass by annealing is covered in chapter 3 and an analysis of laser processing of ion-exchanged glasses is shown in chapter 4. The concluding chapter consists of a summary of the work and an outlook.

Thesis (M.S.)--West Virginia University, 2005.<br>Title from document title page. Document formatted into pages; contains x, 133 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 116-118).

Thesis (M.S.)--West Virginia University, 2009.<br>Title from document title page. Document formatted into pages; contains xi, 71 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 69-71).

In this thesis, nanosecond pulsed lasers are used as the tools to generate microstructures on metal and glass. The applications of these structures are described too. The production of micro structures is demonstrated using diode-pumped solid state (DPSS) Nd:YVO4 lasers operating at wavelengths of 532nm or 1064 nm. The laser fluence and scanning speed are important parameters to control the results. The first part of thesis is on the laser generation of microstructures on metal surfaces. Copper (Cu) and titanium (Ti) have been studied. According to the reflectivity of metals, Cu is processed by a 532nm laser and Ti is processed by a 1064nm laser. It is shown that the periods of surface microstructures are highly dependent on the hatch distance (overlapping distance between laser scanning). Only if the laser fluence is greater than a threshold, may the microstructures on metals be induced. The thresholds are measured by the diameters of ablated areas at different fluence. Laser generated surface microstructures have been applied to modify the reflectivity of a Cu sample. It was found that laser induced surface microstructures on Copper can decrease the surface reflectivity by almost 97% between 250 nm and 700 nm. To find the mechanism of how to form microstructure on metal surface with laser, laser ablation and heating models have been studied. The 1D ablated numerical model is calculated in Matlab. The pressure of metal vapour is an important parameter, as it pushes the melted metal out of surface to form microstructures after re-solidification. The second part of thesis is on glass welding with microstructures on glass surfaces. The soda-lime glasses containing silver nanoparticles (from the company Codixx) have been studied and welded with Schott B270 glass. Compared with other techniques for welding glass, lasers offer the advantage of a relatively simple and flexible technique for joining the local area underneath the cover glass. Most of the laser energy is deposited in the Ag nanoparticle layer because of the large absorption coefficient at 532 nm. Expanded microstructures generated by the laser are applied to fill the gap between the glass surfaces. This is attributed to the formation of bubbles in the Ag nanoparticle layer after laser processing. The welded samples have the joint strength of 4.9 MPa and have great potential for industrial applications. A 3D analytical model is used to estimate the temperature of the glass after the laser pulse. The increase in temperature is about 129 °C. To induce the bubble in glass, many laser pulses are necessary. This is very different from the results for the metals.

This research work focused to identify the key parameters through systematic approach that influence the interfacial bonding strength between matrix and the glass filler. The enhanced coupling agent of silane due to the nanoclay appropriate concentration interact with the functional groups in the epoxy resin and glass fiber, leads to strong interfacial bonding through the formation of intercalation structure. Henceforth, resulted in increased surface hardness leading improved wear performance of the Glass fiber reinforced nanocomposite.

This research provides a comprehensive investigation in understanding the effect of the addition of graphene nano-platelets (GNP) on the mechanical, tribological and biological properties of glass/ceramic composites. We investigated two kinds of materials namely amorphous matrices like glasses (silica, bioglass) and polycrystalline matrices like ceramics (alumina). The idea was to understand the effect of GNP on these matrices as GNP was expected to behave differently in these composites. Bioglass (BG) was also chosen as a matrix material to prepare BG-GNP composites. GNP can improve the electrical conductivity of BG which can be used further for bone tissue engineering applications. The effect of GNP on both electrical conductivity and bio-activity of BG-GNP composites was investigated in detail. There were three main problems for fabricating these novel nano-composites: 1) Production of good quality graphene; 2) Homogeneous dispersion of graphene in a glass/ceramic matrix and; 3) Retention of the graphitic structure during high temperature processing. The first problem was solved by synthesising GNP using liquid phase exfoliation method instead of using a commercially available GNP. The prepared GNP were ~1 μm in length with a thickness of 3-4 layers confirmed using transmission electron microscopy. In order to solve the second problem various processing techniques were used including powder and colloidal processing routes along with different solvents. Processing parameters were optimised to fabricate glass/ceramic-GNP composite powders. Finally in order to avoid thermal degradation of the GNP during high temperature processing composites were sintered using spark plasma sintering (SPS) technique. Fully dense composites were obtained without damaging GNP during the sintering process also confirmed via Raman spectroscopy. Finally the prepared composites were characterised for mechanical, tribological and biological applications. Interestingly fracture toughness and wear resistance of the silica nano-composites increased with increasing concentration of GNP in the glass matrix. There was an improvement of ~45% in the fracture toughness and ~550% in the wear resistance of silica-GNP composites with the addition of 5 vol% GNP. GNP was found to be aligned in a direction perpendicular to the applied force in SPS. In contrast to amorphous materials fracture toughness and scratch resistance of alumina-GNP composites increased only for small loading of GNP and properties of the composites decreased after a critical concentration. There was an improvement of ~40% in the fracture toughness with the addition of only 0.5 vol% GNP in the alumina matrix while the scratch resistance of the composite increased by ~10% in the micro-ductile region. Electrical conductivity of the BG-GNP composite was increased by ~9 orders of magnitude compared to pure BG. In vitro bioactivity tests performed on BG-GNP composites confirmed that the addition of GNP to BG matrix also improved the bioactivity of the nano-composites confirmed using XRD analysis. Future work should focus on understanding electrical and thermal properties of these novel nano-composites.

The objective of this study is to process and characterize the compatibilized blends of acrylonitrile-butadiene-styrene (ABS) and polyamide-6 (PA6) using olefin based reactive copolymers and subsequently to utilize this blend as a matrix material in short glass fiber (SGF) reinforced composites and organoclay based nanocomposites by applying melt processing technique. In this context, commercially available epoxydized and maleated olefinic copolymers, ethylene-methyl acrylate-glycidyl methacrylate (EMA-GMA) and ethylene-n butyl acrylate-carbon monoxide-maleic anhydride (EnBACO-MAH) were used as compatibilizers at different ratios. Compatibilizing performance of these two olefinic polymers was investigated through blend morphologies, thermal and mechanical properties as a function of blend composition and compatibilizer loading level. Incorporation of compatibilizer resulted in a fine morphology with reduced dispersed particle size. At 5 % EnBACO-MAH, the toughness was observed to be the highest among the blends produced. SGF reinforced ABS and ABS/PA6 blends were prepared with twin screw extrusion. The effects of SGF concentration and extrusion process conditions on the fiber length distribution, mechanical properties and morphologies of the composites were examined. The most compatible organosilane type was designated from interfacial tension and short beam flexural tests, to promote adhesion of SGF to both ABS and PA6. Increasing amount of PA6 in the polymer matrix improved the strength, stiffness and also toughness of the composites. Effects of compatibilizer content and ABS/PA6 ratio on the morphology and mechanical properties of 30% SGF reinforced ABS/PA6 blends were investigated. The most striking result of the study was the improvement in the impact strength of the SGF/ABS/PA6 composite with the additions of compatibilizer. Melt intercalation method was applied to produce ABS/PA6 blends based organoclay nanocomposites. The effects of process conditions and material parameters on the morphology of blends, dispersibility of nanoparticles and mechanical properties were investigated. To improve mixing, the screws of the extruder were modified. Processing with co-rotation yielded finer blend morphology than processing with counter-rotation. Clays were selectively exfoliated in PA6 phase and agglomerated at the interface of ABS/PA6. High level of exfoliation was obtained with increasing PA6 content and with screw speed in co-rotation mode. Screw modification improved the dispersion of clay platelets in the matrix.

The dynamic relaxation characteristics of Matrimid® (BTDA-DAPI) polyimide and several functionalized aromatic polyimides have been investigated using dynamic mechanical and dielectric methods. The functionalized polyimides were thermally rearranged to generate polybenzoxazole membranes with controlled free volume characteristics. All polyimides have application in membrane separations and exhibit three motional processes with increasing temperature: two sub-glass relaxations (ƴ and β transitions), and the glass-rubber (α) transition. For Matrimid, the low-temperature ƴ transition is purely non-cooperative, while the β sub-glass transition shows a more cooperative character as assessed via the Starkweather method. For the thermally rearranged polyimides, the ƴ transition is a function of the polymer synthesis method, thermal history, and ambient moisture. The β relaxation shows a dual character with increasing thermal rearrangement, the emerging lower-temperature component reflecting motions encompassing a more compact backbone contour. For the glass-rubber (α) transition, dynamic mechanical studies reveal a strong shift in Tα to higher temperatures and a progressive reduction in relaxation intensity with increasing degree of thermal rearrangement. The dynamic relaxation characteristics of poly(ether imide) and poly(methyl methacrylate) nanocomposites were investigated by dynamic mechanical analysis and dielectric spectroscopy. The nanoparticles used were native and surface-modified fumed silicas. The nanocomposites display a dual glass transition behavior encompassing a bulk polymer glass transition, and a second, higher-temperature transition reflecting relaxation of polymer chain segments constrained owing to their proximity to the particle surface. The position and intensity of the higher-temperature transition varies with particle loading and surface chemistry, and reflects the relative populations of segments constrained or immobilized at the particle-polymer interface. Dielectric measurements, which were used to probe the time-temperature response across the local sub-glass relaxations, indicate no variation in relaxation characteristics with particle loading. Nanocomposite studies were also conducted on rubbery poly(ethylene oxide) networks crosslinked in the presence of MgO or SiO2 nanoparticles. The inclusion of nanoparticles led to a systematic increase in rubbery modulus and a modest positive offset in the measured glass transition temperature (Tα) for both systems. The sizeable increases in gas transport with particle loading reported for certain other rubbery nanocomposite systems were not realized in these crosslinked networks.