Leonardo C. Simon

Erosion resistance and mechanical properties of silicone nanocomposite insulation

The results of erosion resistance, tensile strength, elongation at break, hardness, and thermal stability measurements are presented for silicone nanocomposites prepared using various nano and micro silica and alumina fillers in a two-part silicone rubber (SiR) matrix. The fillers are used to improve the erosion resistance of SiR, which is necessary for outdoor insulation housing applications. Good dispersion of the fillers is achieved using Triton/sup TM/, a common surfactant. An optimal surfactant concentration imparts good erosion resistance to the nanocomposites in laser heating tests without adverse effects, but excess surfactant has a negative impact on the mechanical properties of the silicone. Thermal gravimetric analysis demonstrated that nano fumed silica imparts better heat resistance to silicone than natural nano silica or nano alumina fillers. Fourier transform infrared spectroscopy analysis of the nanofillers indicated a significantly higher concentration of silanol groups in the nano fumed silica filler than in micro silica. The influence of the increased number of silanol groups on the erosion resistance of the nanocomposites and their mechanical properties is discussed.

Thermal transitions and temperature dependent mechanical behavior of wheat straw/talc isotactic/impact modified polypropylene composites

Dynamic mechanical thermal analysis was used to evaluate temperature-dependent mechanical performance of wheat straw/talc polypropylene composites intended for automotive components as well as thermal properties of the produced formulations. Dynamic mechanical thermal analysis results were also correlated with impact tests and static bending test results. Isotactic and impact-modified copolymer polypropylene composites with various amounts of wheat straw or talc were prepared using extrusion followed by injection molding. Different thermal transitions as well as mechanical performance of the composites were evaluated and the effects of fiber loading, matrix type, filler type and hybridization were studied. Results indicated different mechanical behaviors of the two fillers within and between the two matrices. Modulus retention term and relative storage modulus were used as parameters defining mechanical performance at various temperatures. It was found that wheat straw composites were generally comparable to talc composites with better performance at very low or very high temperature regions. The correlations between the dynamic mechanical loss factor values at room temperature and impact strength data revealed a good relationship only for the isotactic polypropylene composites whereas statistically significant correlations were established between flexural strength and impact data for all formulations.

Improving the Electrokinetic Properties of PDMS With Surface Treatments

PDMS (Polydimethylsiloxane) is widely used as a microfluidic chip material for various applications due to its desirable properties [1, 2]. However PDMS has several drawbacks that limit its utilization in a number of microfluidic applications [1–4]. Properties such as the hydrophobic nature, sample absorption, and low electrokinetic properties (low zeta potential) are some issues that must be considered before using PDMS for numerous applications [3]. In many PDMS based chips electroosmotic pumping is used for fluid flow and sample transport along the microchannel networks. Simplicity of implementation in microfluidic chips, fast response time, and the plug-like velocity profile are the major advantages of electroosmotic flow compared to other fluid pumping techniques [2]. This type of flow utilizes the formation of electric double layer (EDL) in microchannels and the movement of ions under an applied external electric field. Thus, the surface properties of the channel material and liquid properties (ionic concentration, pH, and viscosity) play major roles in electroosmotic pumping for different solutions in microchannels.Copyright