This paper presents a microscale benefit of a secondary flow obtained in a curved rectangular microchannel, which is generally unfavorable and negligible in conventional fluid flow. We have demonstrated the separation and sorting of micro beads by their size using secondary flow. The physical mechanism occurring in the size-selective separation was explained based on the numerical analysis of the characteristic velocity distribution on the cross-sectional plane normal to the main flow stream. The dynamic trajectories of micro beads of different sizes and materials are visualized and compared for the experimental demonstration. We also discuss the effects of both the shape uniformity of the micro beads and the inlet condition on the size-selective separation.
The present work addresses the synthesis of 1,4-bis(2-(4-hydroxyphenyl)-2-propyl)benzene based cyanate ester-silica hybrid (CE-SiO 2 ) nanomaterials by an in situ sol-gel method. The nanomaterials are synthesized using a 1,4-bis(2-(4-cyanotophenyl)-2-propyl)benzene [CE] (organic phase) monomer and tetraethoxysilane (TEOS) (inorganic phase) in the presence of various molar ratios of coupling agents [c-aminopropyltriethoxysilane (APTES) or 3-glycidoxypropyltrimethoxysilane (GPTMS)] through covalent bond interaction.The formation of a covalent bond between the organic and inorganic phases is confirmed by FT-IR.Thermal studies indicate that nanomaterials (CE-SiO 2 ) show a higher T g and thermal degradation temperature when compared with neat CE. Morphological studies confirm the molecular level dispersion of silica and CE resin. From the contact angle measurement, the hybrid materials are seen to possess better hydrophobicity i.e. the contact angle value increases from 89u and 57u to 108u and 78u for water and diiodomethane as a probe liquid respectively, also surface free energy reduced from 32.8 to 19.00 mJ m 22 . These materials are expected to find wide application in the field of microelectronics and optoelectronics.
This paper presents a new polydimethylsiloxane (PDMS) dry-etching method that uses microwave plasma. The applicability of the method for fabricating microstructures and removing residual PDMS is also verified. The etch rate of PDMS was dominantly influenced by the gas flux ratio of CF 4 /O 2 and the microwave power. While the PDMS etch rate increased as the flux ratio of CF 4 was increased, the etch rate decreased as the flux ratio of O 2 was increased. The maximum etch rate of 4.31 μm min −1 was achieved when mixing oxygen (O 2 ) and tetrafluoromethane (CF 4 ) at a 1:2 ratio at 800 W power. The PDMS etch rate almost linearly increased with the microwave power. The ratio of the vertical etch rate to the lateral etch rate was in a range of 1.14-1.64 and varied with the gas fluxes. In consideration of potential applications of the proposed PDMS etching method, array-type PDMS microwells and network-type microprotrusion structures were fabricated. The contact angle was dramatically increased from 104 • (non-etched PDMS surface) to 148 • (etched PDMS surface) and the surface was thereby modified to be superhydrophobic. In addition, a thin PDMS skin that blocked holes and PDMS residues affixed in nickel microstructures was successively removed.
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