Surface modification of polymeric membranes and silicon filters

The first part of the dissertation describes the development of in situ deposition of skin layers onto polymeric membranes containing liquid extractants known as supported liquid membranes. The loss of extractants from the supported liquid membranes is a major impediment to practical applications. The skin layers, formed by interfacial polymerization, encapsulate large extractant molecules within the membranes but allow the transport of small species across the membranes. Polyamide skin layers were successfully deposited by liquid-liquid interfacial polymerization utilizing monomers compatible with the extractants. SEM examination shows the polyamide skin layer to be about 1 mum thick with pore sizes below resolution. Membranes with polyamide skin layers showed a typical flux of 1 mumol/sec.m 2 of Cr(VI), about half that exhibited by similar membranes without skin layers. Epoxy skin layers were deposited on supported liquid membranes containing undiluted amine extractants by liquid-vapor interfacial polymerization. The membranes with the epoxy skin layers showed fluxes in the order of 100 mumol/sec.m 2 in the extraction of acetic acid.; The second part of the dissertation contributes to the deposition of a nanometer thick coating on the surface of silicon filters. In order to manipulate microfluid flow and minimize unspecific protein adsorption, uniform and ultrathin coatings are needed on the surface of microdevices such as microfabricated silicon filters. Coating in organic solution using alkyltrichlorosilane or alkyltrimethoxysilane causes formation of multilayers and submicron aggregates on silicon surfaces due to trace amounts of moisture in the environment and in the organic solution. This work demonstrates a protocol for vapor phase deposition of nanometer thick alkylsilanes at ambient pressure using nitrogen as a carrier gas. The method is particularly advantageous when it is necessary to coat small channels in microdevices, where liquids may have difficult access due to capillary forces. The modified silicon surface was extremely smooth, without observable aggregates by SEM and AFM. Micromachined silicon filters were coated with different alkylsilanes and tested with nitrogen gas and other liquids. Interesting flow rate reversal of water versus ethanol was observed when the minimum channel dimension decreased from 74 mum to 1.8 mum.