PREPARATION AND CHARACTERIZATION OF HIGH-SURFACE-AREA POLYMER SUBSTRATES FOR MICROCALORIMETRY

The preparation and characterization of high-surface-area polymeric su bstrates suitable for the microcalorimetry of protein adsorption are d escribed. High-surface-area polystyrene, poly(styrene-co-butyl methacr ylate) and poly(styrene-co-allyl alcohol) were prepared by adsorbing p olymer from solution onto fumed silica. Verification of adsorption of polystyrene by silica was determined by noting peak shifts of the surf ace silanol group in the infrared. The amount of polymer adsorbed was determined from adsorption isotherms. The minimum thickness of polysty rene required to mask silicon oxide properties was found to be that th ickness at which contact angles became constant, about 35 A. Polymer d ensities were measured. Water contact angles on each polymer surface i ndicate that poly(styrene-co-allyl alcohol) has the surface most wetta ble by water. Polymer-water interfacial energies were estimated from p endant drop results and a harmonic mean equation along with contact an gles. Two methods were used to estimate the polar and dispersion compo nents of the three polymers. Both methods predicted polystyrene to hav e the highest interfacial energy against water, and one method predict ed poly(styrene-co-allyl alcohol) to have the lowest. A Wilhelmy plate study verified the change in interfacial properties as a function of contact time with water. A study of the heats of adsorption of lysozym e by each substrate using a modified Tien-Calvet microcalorimeter demo nstrated the suitability of the substrates for microcalorimetry. (C) 1 996 John Wiley & Sons, Inc.