Charged and uncharged polymers at surfaces: Adsorption and interactions

A comprehensive experimental approach, which includes SFA, Ellipsometry and DLS is used to study the adsorption and interaction characteristics of a hydrophobic-hydrophilic (charged) diblock copolymer (poly(tert-butylmethacrylate)-b-poly(glycidylmethacrylate sodium sulfonate [PtBMA-b-PGMAS]) in added salt and an uncharged hydrophobic polymer in poor solvent as well as their association with surfactant systems at solid-liquid interface. The measured surface interactions between two identical negatively charged polyelectrolyte (PtBMA-b-PGMAS)-coated surfaces show that the range of interaction extends well beyond the contour length of the polyelectrolyte chain and that the interaction range as well as the grafting density depend on the ionic strength of the solution. The adsorption kinetic studies indicate that the adsorption process on hydrophobic solid surfaces occurs through the anchoring of hydrophobic chains of PtBMA-b-PGMAS, the surface densities increase with an increase in the ionic strength of the solution and that there are three distinct stages in the adsorption process: an incubation period, a subsequent fast growth process of the polymer layer, and a plateau (equilibrium) region. The measured surface interactions and the adsorption kinetics in PtBMA-b-PGMAS/oppositely charged surfactant (0.1 cmc CTAB) system at hydrophobized solid-liquid interface show a reduction of the extensibility of polyelectrolyte chains under partially screened conditions. The measured forces of interaction between two uncharged hydrophobic polymer (PPO) coated surfaces in water (poor solvent condition) show an initial marginal repulsion followed by an attractive force. When one PPO surface is replaced by a surfactant (SODS) coated surface, the force profiles clearly show the presence of long range attractive forces due to electrostatic attractive force followed by short range repulsive forces. Quantitative analysis of the surface interaction profiles, surface densities and surface growth kinetics have been presented and tested with different theoretical models.