Royal Society Publishing

Measurement of the hydrodynamic forces between two polymer–coated spheres

P. Bartlett, S. I. Henderson, S. J. Mitchell


The hydrodynamic forces between Brownian spheres are determined from a measurement of the correlated thermal fluctuations in particle position using a new method: two–particle cross–correlation spectroscopy. A pair of 1.3 µm diameter polymer–coated poly(methylmethacrylate) particles were held at separations of between 2 and 20 µm using optical traps. The mobility tensor is determined directly from the statistically averaged Brownian fluctuations of the two spheres. The observed distance dependence of the mobility tensor is in quantitative agreement with low–Reynolds–number calculations.

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