Static and dynamic forces between adsorbed polyelectrolyte layers (quaternized poly-4-vinylpyridine)

Static forces (a combination of steric and electrostatic interactions) and dynamic shear forces (resulting from interactions between polymer chains) w ere measured between quaternized poly-4-vinylpyridine layers (QPVP) adsorbe d onto mica from 1 mM borate buffer with or without added 0.25 M NaCl. At t he polyelectrolyte concentration chosen, 0.4 mg mL(-1), extended layers wer e formed at all adsorption conditions. The adsorbed amount of 98% quaterniz ed poly-4-vinylpyridine was lower at law ionic strength than of 14% quatern ized, and increased with added salt. Layers formed by one-step adsorption s howed a predominantly elastic response to small-amplitude oscillatory shear in the frequency range 0.13-130 Hz. In the case of two-step adsorption, th e confined layers allowed viscous dissipation of similar magnitude as the e lastic, which suggests that additional chains adsorbing at high salt concen tration onto a preformed layer had fewer segments in contact with the solid surface.