Numerical calculations were performed to examine the mechanisms for generation of a retro-reflected wave from the interaction of an evanescent wave with a sub-wavelength structure using the finitedifference time-domain (FDTD) method. The simulation shows that an evanescent wave is reflected from the structure at the interface between a high index dielectric material and a low index material. The reflected evanescent wave couples into the upper medium and radiates its energy forming a retro-reflected wave, which appears as a sharp peak near the edge of the structure when imaging the structure in hyper-numerical-aperture solid immersion microscopy. We propose a simple theory and verify it through FDTD calculation under various circumstances in order to explain peculiar features of this phenomenon. Furthermore, we suggest a way to control the reflection of the evanescent wave by taking advantage of the interference of the evanescent wave inside the structure.

This paper is primarily focused in studying the effects of nanoclay particles such as montmorillonite on improving mechanical and thermal properties of fiber reinforced polymer matrix composite materials. Basic correlations between polymer morphology, strength, modulus, toughness, and thermal stability of thermoset nanocomposites were investigated as a function of layered silicate content. S2-glass/epoxy-clay nanocomposites were manufactured through an affordable vacuum assisted resin infusion method (VARIM). The nanocomposites are formed during polymerization when the adsorbing monomer separates the clay particles into nanometer scales. Transmission electron microscopy (TEM) and wide angle X-ray diffraction(WAXD) were used to characterize the morphology of the dispersed clay particles. The thermal properties such as onset of decomposition and glass transition temperatures were determined by Thermo Gravimetric Analysis (TGA) and Dynamic Modulus Analyzer (DMA). Mechanical properties such as interlaminar shear strength, flexural properties and fracture toughness are also determined for both conventional S2-glass/epoxy composites and S2-glass fiber reinforced nanocomposites. The results show significant improvements in mechanical and thermal properties of conventional fiber reinforced composites with low loading of organo silicate nanoparticles. By dispersing 1% by weight nanosilicates, S2-glass/epoxy-clay nanocomposites attributed to almost 44, 24 and 23% improvement in interlaminar shear strength, flexural strength and fracture toughness in comparison to conventional S2-glass/epoxy composites. Similarly, the nanocomposites exhibit approximately 26 C higher decomposition temperatures than that of conventional composites. This improved properties of fiber reinforced polymer nanocomposites are achieved mostly due to increased interfacial surface areas, improved bond characteristics and intercalated/exfoliated morphology of the epoxy-clay nanocomposites. The TEM observations provide evidence of detailed morphology of the polymer layered-clay nanocomposites.

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The manufacture of continuous fibre-reinforced nanocomposites, E-glass reinforced in a polypropylene (PP) matrix with and without nanoclay, by pultrusion is discussed. Thermal and mechanical characterisation of nanocomposites has been performed and compared with traditional microcomposites. Also, the nanocomposites were characterised by Transmission Electron Microscopy (TEM) and Optical Micrography (OPM). Compressive strength of pultruded polypropylene nanocomposites was improved by improving the yield strength of the surrounding matrix in shear and reducing fibre misalignment in the composite through optimisation of manufacturing process variables. TGA and DSC results show that nanoclay improves thermal stability without any deviation in glass transition temperature and melt temperature. Initially, polypropylene and nanoclay were melt intercalated using a single-screw extruder and the pultruded nanocomposite was fabricated using extruded pre-impregnated (pre-preg) tapes. Compression tests were performed as mandated by ASTM guidelines. OPM was used to examine the failure surfaces. TEM revealed an intercalated morphology. Significant improvements were achieved in compressive strength and compressive modulus with relatively low nanoclay loadings. Mechanical tests were performed for baseline pultruded PP nanocomposite with 0 wt% nanoclay and modified pultruded PP nanocomposite with 3 wt% nanoclay. The tests showed significant improvements in compressive strength (~122%) and shear strength (~60%) in modified pultruded PP nanocomposites in comparison with baseline properties. Uni-axial tensile tests showed a minor increase in tensile strength (~3.4%). Multi-scale simulations of nanoclay/polymer interface behaviour are currently in progress in order to understand the strength enhancement mechanism.

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