Long-term influence of fluid inertia on the diffusion of a Brownian particle.
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.
Dipartimento di Fisica Università degli studi di Napoli, Complesso Universitario Monte S. Angelo, Via Cintia 80126, Napoli, Italy.
Giuseppe
G
Pesce
Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ, United Kingdom.
Giorgio
G
Volpe
Soft Matter Lab, Department of Physics, Bilkent University, Ankara 06800, Turkey and UNAM-National Nanotechnology Research Center, Bilkent University, Ankara 06800, Turkey.
Giovanni
G
Volpe
Dipartimento di Fisica Università degli studi di Napoli, Complesso Universitario Monte S. Angelo, Via Cintia 80126, Napoli, Italy.
Antonio
A
Sasso