Transversal dynamics of paramagnetic colloids in a longitudinal magnetic ratchet.

fearfuljewelerUrban and Civil

Nov 16, 2013 (3 years and 8 months ago)

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1
Transversal dynamics of paramagnetic colloids in a longitudinal magnetic ratchet.
Pietro Tierno

Departament de Qu´ımica F´ısica,Universitat de Barcelona,Mart´ı i Franqu`es 1,08028 Barcelona,Spain
In this talk I will describe the transversal motion of
paramagnetic particles above the magnetic stripe pattern
of a uniaxial garnet film,exhibiting a longitudinal ratch-
et effect in the presence of an oscillating magnetic field
1
.
First I will focus on the behaviour of one colloid.With-
out the field,the thermal diffusion coefficient obtained
by video microscopy is D
0
∼ 10
−4
µm
2
/s.With the field,
the transversal diffusion exhibits a giant enhancement
by almost four decades and a pronounced maximum as
a function of the driving frequency.It is possible to ex-
plain the experimental findings with a theoretical inter-
pretation in terms of random disorder effects within the
magnetic film
2
.
On the second part of this talk I will focus on the collec-
tive dynamics of an ensemble of paramagnetic particles
organized as a one-dimensional chain and driven above
the magnetic film.The centre of mass of the chain shows
a diffusive behavior with mean square displacement ∼ t,
while its end-to-end distance shows anomalous kinetics
with a sub-diffusive growth

t.It is possible to extract
the potential of mean force between the particles within
the chain by invoking the Pope-Ching equation
3
.Thus
the experimental data are interpreted by using the Rouse
model,originally developed for polymers,and all relevant
parameters are extracted experimentally
4
.

ptierno@ub.edu
1
P.Tierno,S.V.Reddy,T.H.Johansen,and T.M.Fischer
Phys.Rev.E 75,041404 (2007);P.Tierno,S.V.Reddy,
M.G.Roper,T.H.Johansen,and T.M.Fischer,J.Phys.
Chem.B,112,3833 (2008).
2
P.Tierno,P.Reimann,T.H.Johansen,and Francesc Sagu´es
Phys.Rev.Lett.105,230602 (2010).
3
S.B.Pope and E.S.C.Ching,Phys.Fluids A 5,1529
(1993);E.S.C.Ching,Phys.Rev.E 53,5899 (1996).
4
P.Tierno,Francesc Sagu´es,T.H.Johansen,and I.M.
Sokolov in preparation.
Junio de 2011,Barcelona Pruebas de la contribuci´on1