Measurement of long-range steric repulsions between microspheres due to an adsorbed polymer.

We have measured the interparticle potential between pairs of micron-sized silica spheres induced by adsorbed polyethylene oxide polymer using a line-scanned optical tweezer. We found this long-range steric repulsion to be exponential over the range of energies (0.1k(B)T-5k(B)T) and polymer molecular weights (452,000-1,580,000) studied, and that the potential scaled with the polymer's radius of gyration R(G). The potential's exponential decay length was about 0.6R(G) and its range was about 4R(G), although both parameters varied significantly from one pair of spheres to another. The potential's exponential prefactor was greater than mean-field predictions.