Kinetic Traps in Polymer Adsorption: Exchange of Polystyrene between the Adsorbed State and a Good Solvent

ABSTRACT The conformations of polystyrene (PS) adsorbed onto silicon oxide from carbon tetrachloride (CCW were investigated through measurements of exchange rates between the adsorbed state and free solution. Infrared spectroscopy in attenuated total reflection (FTIR-ATR) was used to measure PS adsorbed onto oxidized silicon from dilute carbon tetrachloride solution at 25.0 "C. Protiopolystyrene (PS-h; M , = 575 000 or 96 400) was allowed to adsorb for a variable time from a solution of concentration 1 mg mL-1; then this solution was replaced by a solution of deuteriopolystyrene (PS-d; M , = 550000 or 85OOO) at the same concentration. An initial rapid exchange was completed over periods of minutes. No subsequent exchange was detectable over periods up to 10 h, indicating that a major fraction of the adsorbed polymer was kinetically trapped. With increasing surface residence time before exchange, the rapid exchange rate slowed moderately and the trapped fraction (Tf) increased. For exchange of chains of matched chain length, after a residence time of 16 h, Tf = 0.6 ( M , = 550 OOO) and Tf = 1.0 ( M , = 90 OOO). However, Tf extrapolated to zero for residence times less than 1 h. In addition, PS-h could be entirely displaced by CH2C12, indicating for this reason also that the adsorption was reversible in spite of being kinetically metastable. The higher trapped fractions after increased equilibration are tentatively interpreted to reflect logjammed states induced by steric hindrance between intertwined adsorbed chains