Hydrodynamic thickness of interfacial layers obtained by adsorption of a charged diblock copolymer on a selective surface from aqueous solutions

The solution properties of the asymmetric diblock copolymer poly(styrenesulfonate)-poly(vinylpyridine) were investigated using light scattering, viscometry, and fluorescence probing. Adsorption on neutral and electrically charged (selective sorbent) materials was determined using radiolabeled polymer, and the hydrodynamic thickness of adsorbed layers was measured by quasi-elastic light scattering measurements. In water, the copolymer displayed dual hydrophobic properties. Its strongest hydrophobic character, responsible for adsorption on the neutral material poly(tetrafluoroethylene) (Teflon), was abolished by addition of very small amounts of electrolyte, while the volume of the less hydrophobic moieties was pH dependent. The solubility domain of the copolymer was limited to the pH range between 2.5 and 3.8 and an ionic strength of less than 0.01. Micelles formed in water or 0.001 M NaCl solution showed a maximum value of the radius of gyration close to 220 nm. Partially reversible adsorption on positively charged polystyrene latex particles bearing amidine surface groups could involve both hydrophobic and ionic interactions, while the hydrodynamic thickness of the residual interfacial layer after rinsing with solvent was dependent on the initial copolymer concentration in the supernatant phase and on the pH and electrolyte concentration of the final suspending phase. The adsorbed copolymer layer appeared to be well suited to the stabilization of colloids in electrolyte media due to its electrosteric protective effect, which increased with electrolyte concentration.