Longterm Influence of Fluid Inertia on Brownian Motion published in Phys. Rev. E

Longterm influence of fluid inertia on the diffusion of a Brownian particle

Longterm influence of fluid inertia on the diffusion of a Brownian particle
Giuseppe Pesce, Giorgio Volpe, Giovanni Volpe & Antonio Sasso
Physical Review E 90(4), 042309 (2014)
DOI: 10.1103/PhysRevE.90.042309
arXiv: 1402.6913

We experimentally measure the effects of fluid inertia on the diffusion of a Brownian particle at very long time scales. In previous experiments, the use of standard optical tweezers introduced a cutoff in the free diffusion of the particle, which limited the measurement of these effects to times comparable with the relaxation time of the fluid inertia, i.e., a few milliseconds. Here, by using blinking optical tweezers, we detect these inertial effects on time scales several orders longer up to a few seconds. The measured mean square displacement of a freely diffusing Brownian particle in a liquid shows a deviation from the Einstein-Smoluchowsky theory that diverges with time. These results are consistent with a generalized theory that takes into account not only the particle inertia but also the inertia of the surrounding fluid.

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