Abstract
By measuring the changing electrophoretic mobility of single optically trapped silica microspheres (radius a ≈ 0.4 μm) during poly(ethylene oxide) homopolymer adsorption and desorption, we study polymer-layer kinetics at various polymer solution flow rates, concentrations, molecular weights, and polydispersities. At polymer concentrations c ≲ 5 ppm (mg L–1), Peclet numbers Pe ≲ 20, and Reynolds numbers Re ≪ 1, the adsorbing layer growth is mass-transport-limited, with time scales ∼10 s that are resolved on the uniquely small, micrometer length scale of optical tweezers electrophoresis (OTE) experiments. However, during adsorption, layer growth becomes limited by surface diffusion, reconformation, and exchange processes. Two characteristic relaxation times are revealed by the OTE time series. The faster time scale increases with polymer concentration and plateaus to ∼3 s when c ∼ 10 ppm. This reflects layer development kinetics limited by surface diffusion and reconformation. The slower time scale is ∼100 ...
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