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A microfluidics based, localised formation of nylon 6,6 membranes has been undertaken. The study demonstrates the feasibility of maintaining stable aqueous/organic interfaces for xylene within simple linear flow channels. Glass fabricated structures were used with adipoyl chloride and hexamethylenediamine in the organic and aqueous phases respectively, in order to achieve nylon 6,6 interfacial polymerisation. Localised membrane formation was investigated in flow channels of different geometries over a wide range of flow rates (500 to 4000 µl/min), with Reynolds numbers ranging from 8.4 to 67.2. The results demonstrate that interfacial polymerisation occurs consistently over a wide range of flow rates and of flow entry angles for dual aqueous/organic solvent input. However, creation of uniform planar film structures required careful optimisation, and these were best achieved at 2000 µl/min with a flow entry angle of 45º. The resulting membranes had thicknesses in the range between 100 and 300 µm. Computational modelling of the aqueous/organic flow was performed in order to characterise flow stability and wall shear stress patterns. The flow arrangement establishes a principle for the fabrication of micromembrane structures designed for low sample volume separation, where the forming reaction is a facile and rapid interfacial process.

We report a novel technique for preparing cross-linked protein membranes within microchannels by using an interfacial cross-linking reaction. Glass microchannels with a Y input were assembled by using a simple adhesive bonding technique to achieve dual, parallel laminar flows. Membrane formation utilised an interfacial reaction at the liquid-liquid interface, which involved bovine serum albumin (aqueous solution with a flow rate of 300 microL min(-1)) and terephthaloyl chloride (xylene solution with a flow rate of 700 microL min(-1)), to form thin ( approximately 25 microm) cross-linked films along the length of the channel under the continuous pressure-driven laminar flow. Such microfabricated membranes could extend the separation potential of any microfluidic structure to provide a stable barrier layer. Furthermore, degradation of the membrane was possible by using an alkali sodium dodecyl sulfate solution, which led to the complete disappearance of the membrane. These membranes could facilitate additional modification to allow for different permeability properties by controlled degradation. The one-step in situ membrane-fabrication methodology reported here generated precisely localised membranes and avoided the complexities of subcomponent assembly, which require complicated alignment of small, preformed membranes. This methodology could become the basis for sophisticated microseparation systems, biosensors and several "lab-on-a-chip" devices.

A suitable redox titration procedure has been standardized and the effect of sodium borohydride in various vat dyebaths has been studied. An analysis of the redox curve gives valuable data on the stability of the reducing system, leucopotential of the dye, and over-all stability of the dyebaths. It is shown that sodium borohydride does not improve the stability of the dyebath against oxidation. In certain systems, it even shows adverse effects. Results indicated that sodium borohydride cannot be a total or partial substitute for sodium hydrosulfite in current vat dyeing practice. This finding has been verified by hank-dyeing. In vatting and dyeing, the specificity of a reducing agent appears to be more important than its reduction potential.

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