Solvency effects in polymer layers studied by electrokinetics: PVME as homopolymer and in an anionic diblock copolymer adsorbed on SiO2

The adsorption from aqueous solution of polyvinylmethylether (PVME) and poly(vinylmethylether)-block-poly(vinyloxy-4-butyric acid) (PVME-b-PVOBA) on SiO2 and the effect on the electrophoretic mobility of SiO2 particles was studied at different temperatures and pH values. The temperature range included the lower critical solution temperature (LCST) of PVME, above which the polymer becomes insoluble. The negatively charged block copolymer starts to form micelles a few degrees above the LCST of PVME. Upon adsorption of PVME below the LCST, the SiO2 particles showed a decreasing electrophoretic mobility with increasing PVME dosage. With increasing temperature, a sharp increase in the mobility occurs at the LCST of PVME. At temperatures above the LCST, the mobility is about the same as of the uncovered particles. The PVME-b-PVOBA block copolymer adsorbs on SiO2 with its PVME block, while the negatively charged PVOBA block protrudes into the solution. SiO2 dispersions with PVME-b-PVOBA at neutral pH and below the temperature where micelles are formed (Tmic) have a constant value for the mobility at a level below that of the bare particles, independent of polymer concentration. A large increase in mobility occurs at Tmic leading to mobilities which are higher than of the uncovered particles. Probably, surface micelles and a highly charged brush are formed. No change in the mobility occurs at the LCST of PVME, which is a few degrees below Tmic. The adsorption of PVME-b-PVOBA dominates the mobility of the SiO2 particles even at low pH values. The difference in effect on the mobility of SiO2 particles with PVME and PVME-b-PVOBA is ascribed to the presence of charged groups in the PVOBA block which are expected to be located near the slipping plane.