Factors influencing the adhesion of polystyrene spheres attached to pyrex by polyethyleneimine in aqueous solution

Polystyrene spheres (5 μm in diameter) were deposited onto the inside surface of a glass capillary which was covered with adsorbed polyethyleneimine (PEI). From the flow rates of liquid through the capillary which were required to remove the spheres, sphere-PEI-glass adhesion forces were measured as functions of pH, molecular weight of the PEI, NaCl concentration, deposition time, and the PEI concentration of the solution used to form the adsorbed layer. Supplementary measurements of streaming potentials (capillary/liquid interface), PEI charge, and PEI adsorption on glass, were considered in the interpretation of the adhesion results. The average bond strengths (ABS) varied from 0.05 to >4.5 nN. Adhesion was low at pH 3 and was maximal between pH 10 and 11. The ABS was approximately independent of NaCl concentration. Each 10-fold increase in the average molecular weight of the PEI resulted in an approximately 2-fold increase in the ABS. Reciprocating flow in the capillary caused the attached spheres to oscillate with an amplitude of ca. ± 1.5 μm.