APS March Meeting 2012
Volume 57, Number 1
Monday–Friday, February 27–March 2 2012;
Boston, Massachusetts
Session T48: Focus Session: Advanced Optical Probes of Soft Matter - Microrheology, Microbiography
2:30 PM–5:30 PM,
Wednesday, February 29, 2012
Room: 161
Sponsoring
Units:
DPOLY DBIO
Chair: Daneil Ou-Yang, Lehigh University
Abstract ID: BAPS.2012.MAR.T48.7
Abstract: T48.00007 : Brownian motion goes ballistic*
3:42 PM–4:18 PM
Preview Abstract
Abstract
Author:
Ernst-Ludwig Florin
(University of Texas at Austin)
It is the randomness that is considered the hallmark of Brownian motion, but
already in Einstein's seminal 1905 paper on Brownian motion it is implied
that this randomness must break down at short time scales when the inertia
of the particle kicks in. As a result, the particle's trajectories should
lose its randomness and become smooth. The characteristic time scale for
this transition is given by the ratio of the particle's mass to its viscous
drag coefficient. For a 1 $\mu $m glass particle in water and at room
temperature, this timescale is on the order of 100 ns.
Early calculations, however, neglected the inertia of the liquid surrounding
the particle which induces a transition from random diffusive to
non-diffusive Brownian motion already at much larger timescales. In this
first non-diffusive regime, particles of the same size but with different
densities still move at almost the same rate as a result of hydrodynamic
correlations. To observe Brownian motion that is dominated by the inertia of
the particle, i.e. ballistic motion, one has to observe the particle at
significantly shorter time scales on the order of nanoseconds. Due to the
lack of sufficiently fast and precise detectors, such experiments were so
far not possible on individual particles.
I will describe how we were able to observe the transition from
hydrodynamically dominated Brownian motion to ballistic Brownian motion in a
liquid. I will compare our data with current theories for Brownian motion on
fast timescales that take into account the inertia of both the liquid and
the particle.
The newly gained ability to measure the fast Brownian motion of an
individual particle paves the way for detailed studies of confined Brownian
motion and Brownian motion in heterogeneous media.
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[1] Einstein, A. \"{U}ber die von der molekularkinetischen Theorie der
W\"{a}rme geforderte Bewegung von in ruhenden Fl\"{u}ssigkeiten
suspendierten Teilchen. Ann. Phys. 322, 549--560 (1905).
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[2] Lukic, B., S. Jeney, C. Tischer, A. J. Kulik, L. Forro, and E.-L.
Florin, 2005, Direct observation of nondiffusive motion of a Brownian
particle, Physical Review Letters 95, 160601 (2005).
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[3] Huang, R., Lukic, B., Jeney, S., and E.-L. Florin, Direct observation of
ballistic Brownian motion on a single particle, arXiv:1003.1980v1 (2010).
\\[0pt]
[4] Huang, R., I. Chavez, K.M. Taute, B. Lukic, S. Jeney, M.G. Raizen, and
E.-L. Florin, 2011, Direct observation of the full transition from ballistic
to diffusive Brownian motion in a liquid, Nature Physics 7, 576--580 (2011).
*This research was supported by NSF grants PHY-0647144 and DBI-0552094
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2012.MAR.T48.7