Papers by Author: Yiu Wing Mai

Abstract: The concept of introducing self-healing capabilities in polymer materials and systems has been based on mimicking biological self-healing materials and systems, for example, materials like proteins have phenomenal capabilities in self-healing damaged biological structures. This work has been extended to investigate self-healing capabilities of fibre reinforced epoxy composites. Microencapsulated epoxy and mercaptan healing agents were incorporated into a glass fibre reinforced epoxy matrix to produce a polymer composite capable of self-healing. The specimens containing the microencapsulated epoxy and mercaptan healing agents did gain excellent strength and achieved a healing efficiency up to 140%.

Abstract: Tensile tests were conducted on nylon 6/clay nanocomposites, with and without POE-g- MA rubber particles, over a range of temperatures below the glass transition and strain rates 10-4 to 10-1 s-1. It was shown that the yield strength varied with temperature and strain rate as the Eyring equation thus providing results on activation energy and activation volume for the physical mechanisms involved in these processes. Additionally, the tensile dilatometric responses indicated that the presence of POE-g-MA rubber particles did not alter the shear deformation mode of neat nylon 6. In contrast, the presence of clay layers changed the tensile yield deformation of nylon 6 from the more deviatoric plasticity to the more dilatational plasticity. In nylon 6/clay/POE-g-MA ternary nanocomposite, the volume strain response showed that POE-g-MA rubber particles promoted shear deformation and clay layers delamination was suppressed at yield.

Abstract: A novel solid state and surfactant-free method has been developed for synthesis of polyaniline superstructure composed of dendritic nanofibers. The good crystallinity of the product is confirmed by XRD, while FT-IR analyses indicate the formation of highly doped emeraldine salt of polyaniline product. Microscopic observations show that the product is in the form of polyaniline dendrites with a less-than-40 nm fiber diameter. The unique growth mechanism of the superstructure in solid-state reaction has been discussed.

Abstract: Ca-containing anodic alumina (CAA) has been successfully prepared by anodizing Al film in an alkali solution at a constant voltage and subsequently electro-depositing calcium salts on and into porous anodic alumina. This paper studied the induction ability of Ca-containing anodic alumina (CAA) for calcium phosphates salts by immersing CAA in a simulated body fluid (SBF). The morphologies and compositions of the inductive coating are studied in depth using SEM and XRD. The results show that the porous Ca-containing anodic alumina (CAA) exhibits good induction ability of calcium phosphates in SBF. The Ca/P atomic ratio of the inductive coating on CAA after 7 days immersion in SBF is of 1.68 and the inductive coating on CAA is apatite. Consequently apatite /Al2O3 (anodic) composite has been obtained after apatite inductively formed on Ca-containing anodic alumina. Tafel polarization test indicates that apatite /Al2O3 composite has good anti-corrosion ability in simulated body environment. Therefore, Ca-containing anodic alumina films are promising substrates for fabricating functional coatings and its inductively formed apatite/Al2O3 composite is a promising material for hard tissue repair applications.

Abstract: Ca-containing anodic alumina (CAA) has been successfully prepared by anodizing Al film in an alkali solution at a constant voltage and subsequently electro-depositing calcium salts on and into anodic alumina. This paper investigated the anodic behavior of Al, deposition behavior of calcium salt, and microstructure of CAA. The results show that the anodic behavior of Al in Na3PO4 electrolyte can be described as three continuous stages as of initial growth of the compact barrier layer, formation of porous alumina and further development of its pores and columnar holes. It is also found that cell voltage of electro-deposition process plays an important role at the deposition behavior of calcium slat and the microstructure of Ca-containing anodic alumina (CAA). The higher the cell voltage is, the faster the deposition rate, and the more calcium being deposited at the surface of anodic alumina and into the columnar holes or at the walls of the holes of anodic alumina. It is expected that Ca-containing anodic alumina films are promising substrates for fabricating functional bio-coatings for prosthetic applications.

Abstract: In the present paper, continuum fracture mechanics is used to analyze the Smart-Cut process, a recently established ion cut technology which enables highly efficient fabrication of various silicon-on-insulator (SOI) wafers of very high uniformity in thickness. Using integral transform and Cauchy singular integral equation methods, the mode-I and mode-II stress intensity factors, energy release rate and crack opening displacements are derived in order to examine several important fracture mechanisms involved in the Smart-Cut process. The effects of defect interaction and stiffening wafer on defect growth are investigated. The numerical results indicate that a stiffener/handle wafer can effectively prevent the donor wafer from blistering and exfoliation, but it slows down the defect growth by decreasing the magnitudes of SIFs. Defect interaction also plays an important role in the splitting process of SOI wafers, but its contribution depends strongly on the size, interval and internal pressure of defects. Finally, an analytical formula is derived to estimate the implantation dose required for splitting a SOI wafer.

Abstract: Nylon 6/clay nanocomposites are comprised of nylon 6 matrix filled with montmorillonite platelets (MMT) [1, 2]. It is interest that the MMT offered exceptional reinforcing effect (such as modulus) at a low filler content[3]. Models for predicting properties of fiber composites[4-8] and their developed models[9, 10] based on the supposition of possible microstructure around the MMT platelets have been conducted with the aim of predicting the stiffening effect of the MMT in nanocomposites.

Abstract: In contrast to the classical composites, microfibrillar reinforced composites are not prepared via melt blending of the matrix and the reinforcing material. In fact, the reinforcing elements of this composite, the microfibrils, are created during processing. This advantage allows the manufacturing of a full biodegradable composite material with improved mechanical properties. Basing on a blend of two common biodegradable polymers, polylactide and polyglycolide, this new composite shows promising values under ambient conditions.