| Abstract
| - We have engineered a new class of pH-responsive polymer films on gold surfaces by firstdeveloping a controlled, surface-catalyzed polymerization to prepare a copolymer film consistent with poly(methylene-co-ethyl acetate) and subsequently hydrolyzing the ester side chains to varying extents to yieldcarboxylic acids (denoted as PM-CO2H). When pH is increased, the acid groups become deprotonated orcharged, dramatically increasing their water solubility and greatly altering the film properties. The carboxylicacid content within the copolymer film can be adjusted by changing the monomer concentration ratio usedin the polymerization process or the length of time for the hydrolysis. We have designed PM-CO2H filmsto consist predominately (>95%) of polymethylene (PM) so that the film is hydrophobic in the unchargedstate and, thereby, exhibits an extremely large pH-induced response in barrier properties once ionized.The effect of polymer composition on pH response was investigated by electrochemical impedancespectroscopy (EIS), reflectance-absorption infrared spectroscopy (RAIRS), and contact angle measurements.At a 1%−4% molar acid content, the copolymer film exhibits a 5 orders of magnitude change in its resistanceto ion transport over 2−3 pH units. The pH at which this response begins can be tailored from pH 5 to pH10 by decreasing the acid content in the film from 4% to 1%.
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