pH-Responsive Thin Film Membranes from Poly(2-vinylpyridine):  Water Vapor-Induced Formation of a Microporous Structure

Abstract

We report the fabrication of microporous thin film membranes with two-dimensionally arranged submicron pores whose size can be varied by changing pH of aqueous medium. A solution containing poly(2-vinylpyridine) partially quaternized with 1,4-diiodobutane (qP2VP) and unreacted 1,4-diodobutane (DIB) was used for the formation and deposition of the membranes on solid substrates. The membranes were spin-coated onto solid substrates in a controlled humid environment. The presence of water vapor in air was found to be a necessary condition for the pore formation. We studied the influence of relative humidity on the membrane morphology and proposed a mechanism of pore formation. Cross-linking the qP2VP membranes with DIB made them insoluble (stable) in organic solvents and acidic water. The cross-linked membranes demonstrated pHdependent swelling, which had a strong influence on the pore size. IntroductionMicroporous polymer membranes (pore size 0.01-20 µm) are widely used in industry, medicine, pharmacology, and research for separation and concentration of particles, colloids, proteins, enzymes, and cells. Phase inversion and track etching are well-established, commercially implemented techniques for the fabrication of such membranes. In the phase inversion technique, a solvent for a polymer turns into a nonsolvent causing the polymer precipitation; the nonsolvent serves as a porogen that evaporates after the membrane formation. Phase inversion is usually achieved by immersion of a solution film into a coagulation bath with a nonsolvent (immersion precipitation), by exposure to nonsolvent vapor, or by temperature change (temperature-induced phase separation). Membranes prepared by this technique exhibit a highly porous inner structure represented by a continuous network of interconnected tortuous pores. Furthermore, the structure is usually asymmetric with a thin dense surface layer and a thick spongelike basic layer. The surface layer determines the separation properties and the overall flow resistance of the membrane, while the basic layer acts as a mechanical support. 1 The track etch (TE) membranes are prepared using a two-step fabrication procedure. 2 First, a polymer film (polycarbonate or polyester) is exposed to a collimated beam of heavy ions that produce parallel tracks across the film. The tracks are then chemically etched, forming cylindrical pores. Unlike the phase inversion membranes, the track etch membranes are characterized by uniform pore size and relatively low pore density, resulting in the high flow resistance.In addition to the above-mentioned techniques, various template-assisted methods for the fabrication of microporous polymer membranes have been reported in the literature. Colloidal crystals 3-8 and emulsion droplets 9 have been successfully implemented as templates for the fabrication of selfstanding membranes. Microcontact molding 10 and casting of polymer layers on solid substrates with 2D pillar arrays 11 were found to be feasible for the fabrication of thin film membranes.

Core-Sheath Nanofibers as Drug Delivery System for Thermoresponsive Controlled Release

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Droplet condensation on polymer surfaces: A review

“…These membranes were cross-linked by temperature annealing and after cross-linking membranes demonstrated pH-dependent swelling, which makes them potentially attractive for size dependent filtering, drug delivery systems, and sensors. 227 Munoz Bonilla et al obtained breath figure patterns on functional surfaces by the surface segregation of a statistical glycopolymer, (S-co-2-(D-glucopyranosyl) aminocarbonyloxy ethyl acrylate. The blends of this copolymer and high-molecular-weight PS were spin coated from THF solutions and it was shown that blend composition and relative humidity play an important role in the size and distribution of the pores.…”

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