Journal of Nano Research Vol. 23

Abstract: Polylactides (PLA) based composite films modified with nanoclay content ranges from 0-30 wt% were fabricated using solvent casting method and the mechanical properties, water vapor permeability, oxygen barrier, thermal stability and optical properties were studied. The study showed that the addition of up to 15 wt% of clay has caused a significant improvement of tensile strength of the PLA/nanoclay composite film. However, the further increasing of nanoclay content of >15 wt% of nanoclay has caused a significant reduction in tensile, elongation at break and optical properties of PLA matrix. Both the oxygen and water permeability of the PLA/nanoclay composite film decrease with the increasing of nanoclay contents. Greater water barrier properties would be achieved if the high nanoclay contents of 10-30 wt% were dispersed homogenous within the PLA matrix. The addition of nanoclay greater than 10 wt% affected the appearance of the film (i.e. increasing the haze and ΔE). Thermal analysis result has proved that the melting temperature, crystallization temperature and glass transition temperature of the composite film only slightly affected by the addition of nanoclay due to the immobilization polymer chain in the composite film.

Abstract: Glass transition temperature T_g is the most important parameter affecting the mechanical properties of amorphous and semi-crystalline polymers. However, the atomistic origin of glass transition is not yet well understood. Using Polyethylene (PE) as an example, this paper investigates the glass transition temperature T_g of PE with the aid of molecular dynamics (MD) simulation. The effects of PE chain branches, crystallinity and carbon-nanotube (CNT) additives on the glass transition temperature are analyzed. The MD simulations render a good agreement with the relevant experimental data of semi-crystalline PE and show the significant effects of crystallinity and addition of CNTs on T_g.

Abstract: To study the influence of twice-deposited mask layers on the verticality of side wall and the aspect ratios of silicon-based nanostructures, the performance of focused ion beam (FIB) and CF₄-based inductive coupled plasma reactive ion etching (ICP-RIE) processes was realized. The first etching mask of chromium (Cr) was deposited by radiofrequency (RF) magnetron sputtering as the conductive and etching barrier layers. Next, the Cr layer was directly patterned by a dual-beam FIB system to form nanograting patterns. Thereafter, a secondary mask layer of oxide (SiO₂) with a thickness of 50 nm was deposited by sputtering. In order to study the influence of various deep etching parameters on verticality and aspect ratios, we examined argon flow rates, coil powers, platen powers, and chamber pressures. The SiO₂ barrier layer on the side wall could be retained to maintain a high verticality contour and reduce the line-width shrinking ratio to surmount over etching during the use of fluorine-based gas. The residual Cr and SiO₂ layers were dissolved and removed using a wet etching process consisting of a Cr-etching solution (CR-7). Measurements show that the verticality and aspect ratios of the grating nanostructures were 92.1° and 5.63, respectively.

Abstract: Micro metal injection molding has become the promising method in powder metallurgy research in order to fabricate small-scale intricate parts in an influential process and competitive cost of mass production. Stainless steel 316 L powders with powder size of 150 nm and 5 μm were mixed with a binder with a water soluble component which consisted of a major fraction of water soluble Polyethylene Glycol (PEG), a minor fraction of polymethyl-methacrylate (PMMA) and some stearic acid has been used as a surfactant. This work aims to investigate the rheological properties of a feedstock which are efficiently characterised by capillary Rheometry to measure apparent viscosities at different temperatures and shear rates. Results obtained by the varying feedstock characteristics, when viscosity decreases by increasing of shear rate at certain temperature feedstock should have a pseudoplastic behaviour. Melt viscosity of the feedstock was decreased by adding nanoscale powders. The reduced (n) values at high temperature with addition of nanoparticles indicated a possible increase in the shear-thinning behavior.

Abstract: Different types of defects can be introduced into graphene during material synthesis, and significantly influence the properties of graphene. In this work, we investigated the effects of structural defects, edge functionalisation and reconstruction on the fracture strength and morphology of graphene by molecular dynamics simulations. The minimum energy path analysis was conducted to investigate the formation of Stone-Wales defects. We also employed out-of-plane perturbation and energy minimization principle to study the possible morphology of graphene nanoribbons with edge-termination. Our numerical results show that the fracture strength of graphene is dependent on defects and environmental temperature. However, pre-existing defects may be healed, resulting in strength recovery. Edge functionalization can induce compressive stress and ripples in the edge areas of graphene nanoribbons. On the other hand, edge reconstruction contributed to the tensile stress and curved shape in the graphene nanoribbons.

Abstract: A large-scale molecular dynamics simulation was used to investigate the propagation of cracks in three dimensional samples of nanocrystalline copper, with average grain sizes ranging from 5.34 to 14.8 nm and temperatures ranging from 1K to 500 K. It was shown that intragranular fracture can proceed inside the grain at low temperature, and plastic deformation around the tip of the crack is accommodated by dislocation nucleation/emission; indeed, both fully extended dislocation and deformation twinning were visible around the tip of the crack during fracture. In addition, due to a higher concentration of stress in front of the crack at a relative lower temperature, it was found that twinning deformation is easier to nucleate from the tip of the crack. These results also showed that the decreasing grain size below a critical value exhibits a reverse Hall-Petch relationship due to the enhancing grain boundary mediation, and high temperature is better for propagating ductile cracks.

Abstract: A simple gamma irradiation strategy was developed for the synthesis of gold nanoplates by employing polydiallyldimethylammonium chloride (PDDA) as the capping agent. The nanoplates produced had hexagonal, triangular and truncated triangular shapes and the size of the nanoplates could be varied from 500 nm to 5 μm by adjusting the concentration of Au³⁺ and PDDA in the solution. X-ray diffraction and selected area electron diffraction investigations proved that the nanoplates are single crystals bound by the {111} planes on the top and bottom surfaces. The nanoplates were also characterized by energy dispersive X-ray analysis and X-ray photoelectron spectroscopy.

Abstract: The clinical application of antioxidants as pharmaceutical agents has been limited in general because of their poor aqueous solubility and inferior stability. According to previous studies, nanocarrier drug delivery systems may provide an alternative way to solve the above problems. In this study, nanoparticle carriers consisting of 6-hydroxy-2, 5, 7, 8-tetramethylchroman-2-carboxylic acid (Trolox) encapsulating hydroxy-terminated poly (amidoamine) dendrimer (PAMAM-OH) were prepared by a self-assembly method and characterized by size, size distribution and morphology. A drug release assay showed that the Trolox release from PAMAM-OH/Trolox exhibits pH dependence. Moreover, the effects of PAMAM-OH/Trolox on cells damaged by tert-butylhydroperoxide were determined by 3-(4, 5-dimethylthizaol-2-yl)-2, 5-diphenyl tetrazolium bromide assay for cell viability, and malonaldehyde assay for membrane lipid peroxidation. The results illustrated that the PAMAM-OH/Trolox can significantly improve cell viability and reduce MDA content compared with those of cells pretreated with free Trolox.

Abstract: A modeling study on energy absorption and transport in an isolated nanoshell and aggregates of nanoshells under localized surface plasma resonance (SPR) conditions is presented. A comprehensive model for multi-scattering of electromagnetic waves by a cluster of multilayered nanoshells is developed, which applies the Wigner-Eckart theorem for the calculation of the total scattering cross sessions of nanoshell aggregates. Absorption by an isolated nanoshell and by nanoshell clusters is studied using the model. Results show that the inter-nanoshell coupling results in strong field enhancement near the particle surface. Energy absorption in a nanoshell can be tuned by varying the structural parameters of the nanoshell. Smaller particles are more absorbing than the large ones, other conditions being equal. Because of the presence of a dielectric cavity, the radial distribution of the absorbed power in the metal shell may differ from the classical skin depth phenomena. The interaction among particles in close proximity causes the energy absorption efficiency and the resonance position of a nanoshell cluster to differ from those of an isolated nanoshell.