MEASUREMENT OF THE SEGMENTAL ADSORPTION ENERGY OF POLY(2-ETHYL-2-OXAZOLINE) ON SILICA IN WATER AND ETHANOL

The segmental adsorption energy parameter, chi(s)(po), was measured for poly(2-ethyl-2-oxazoline), PEOX, using a desorption/displacement technique. PEOX was desorbed from silica with five low molecular weight organic displacers in two solvents-water and ethanol-to obtain values of the critical volume fraction of the displacer at which the desorption was complete, phi(cr). The segmental adsorption energy for PEOX was 5.1 kT and 3.2 kT in water and ethanol, respectively. These values are consistent with the polymer adsorbing principally by hydrogen bonding between the carbonyl groups on the polymer and surface silanol groups. The difference in adsorption energies in water and ethanol reflects specific solvent effects that may be related to the negative excess entropy of mixing for water in PEOX solutions as well as due to the formation of hydrogen bond bridges between PEOX and silanol groups in water. The relatively high values of chi(s)(po) for PEOX in both solvents suggest that PEOX may serve as an effective anchor block in block copolymers adsorbing on surfaces by hydrogen bonding.