Preparation of Hydrophilic Poly(Vinylidene Fluoride) Membranes for Molecular-Scale Separation
Abstract
We designed a molecular-scale separation system with a hydrophilic membrane surface containing a uniform channel size distribution. The essential concept is the introduction of an amphiphilic comb copolymer, whose microphase-separated structure of interconnnected domains serves as channels with controlled domain sizes for water molecules on a non-porous membrane surface. We first demonstrate this system with a comb copolymer containing polyvinylidene fluoride (PVDF) and polyoxyethylene methacrylate (POEM), PVDF-g-POEM. The solvent-cast film of this copolymer displays a hydrophilic surface and rejects > 99 wt% of oil from stabilized oil/water emulsion feed at 400 psig. Then, applying our surface self-organization technique, we introduce this comb copolymer as an additive into the casting solution of the PVDF membrane via immersion precipitation to process a much thinner surface layer of dense non-porous PVDF-g-POEM, with a porous asymmetric sublayer of PVDF. We show that this surface-modified membrane exhibits similar wettability to that of the pure PVDF-g-POEM thin film, resulting in 30-40 times enhancement in flux for both pure water and oil/water filtration, compared with the control PVDF membrane. Next, exploiting the microphase-separated structure at the membrane surface, we demonstrate the potential use of this surface-modified membrane for precise molecular selectivity in organic dye filtration experiments. The nano-scale hydrophilic channels display complete retention of larger molecules of Alcian Blue dyes, in opposition to complete permeation of smaller molecules of Rhodamine B dyes. Moreover, since we have the capability to design the size of hydrophilic channels through controlled synthesis, we also engineer this surface-modified membrane to enhance the uniformity in size distribution of metal nanoparticles, a valuable tool for opto-electronic devices.
- Publication:
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APS March Meeting Abstracts
- Pub Date:
- March 2003
- Bibcode:
- 2003APS..MARH16003A