Measurement of long-ranged steric forces between polyelectrolyte layers physisorbed from 1 M NaCl

The colloidal probe technique (CPT) is used to measure distance-dependent interaction forces between polyelectrolyte layers physisorbed from 1 M NaCl solution in salt solutions between 0.1 mM and 1 M. Both linear polycations (poly(allylamine)hydrochloride, poly-L-lysine) and linear polyanions (poly(styrenesulfonate)) are used. The repulsive interaction energies in the range between 10(-7) and 10(-4) J/m2 are described by the theory of Alexander and de Gennes for surfaces covered with neutral anchored polymers. However, the brush thickness scales with molecular area and salt concentration with a power of -1/3 as known from a salted brush and reaches approximately 50% of the contour length in diluted solutions. The findings are confirmed by CPT images using a gold layer as height reference.