Influence of Cross-Linking and Process Parameters on the Separation Performance of Poly(dimethylsiloxane) Nanofiltration Membranes

Abstract

The flux of an organic solvent and the rejection of organic solute molecules was studied using dense poly(dimethylsiloxane) (PDMS) membranes with different degrees of crosslinking. It was found that the transport mechanisms favoured the pore-flow concept rather than a solution-diffusion approach, and that the effective pore size of the membrane was dependent on the degree of crosslinking (and swelling propensity of the feed stream). PDMS membranes with a high degree of crosslinking gave lower solvent fluxes and increased solute rejections, implying a smaller pore size than equivalent membranes with a lower degree of crosslinking. Based on the rejection of a low-polarity poly-nuclear aromatic solute in a xylene solvent, the effective membrane pore diameter is shown to vary between 1.7 and 2.4 nm depending on the degree of crosslinking. A comparison of thirteen different PDMS samples with varying thickness and crosslinking showed a correlation between solvent induced membrane permeability, solute rejection and effective membrane pore size. The results suggests that if the thickness of the PDMS layer is known, the effective pore size and separation performance of crosslinked PDMS membranes can be determined by a simple measurement of solvent flux.