Abstract
The wetting behavior of phase-separated aqueous solutions of dextran and poly (ethylene glycol) on quartz substrates coated with covalently bound dextran fractions was examined as a function of coating molecular weight. The effect of dissolved polymer size was also investigated by using two-phase test systems containing high and low molecular weight dextrans. Sharply cut dextran fractions of Mw from 27,900 to 205,000 were attached to quartz activated with 3-aminopropyldimethylethoxysilane through reductive amination of the dextran's reducing end group in the presence of sodium cyanoborohydride. X-ray photoelectron spectroscopy and contact angle measurements in the two-phase polymer solutions were used to assess the quantity and quality of the surface coatings. Our results demonstrate that wetting by the dextran-rich phase improves, as evidenced by a declining contact angle, with increasing molecular weight of the bound dextran, decreasing molecular weight of the free dextran in solution and increasing time of exposure to the polymer phases. The usual relationship of increasing contact angle with increasing interfacial tension is not observed in these phase-separated polymer mixtures.
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