Numéro |
J. Phys. II France
Volume 4, Numéro 6, June 1994
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|
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Page(s) | 1061 - 1074 | |
DOI | https://doi.org/10.1051/jp2:1994184 |
J. Phys. II France 4 (1994) 1061-1074
Electro-optic effects of aqueous fd-virus suspensions at very low ionic strength
H. Kramer1, C. Graf1, M. Hagenbüchle1, C. Johner1, C. Martin1, P. Schwind2 and R. Weber11 Fakultät für Physik, Universität Konstanz, 78434 Konstanz, Germany
2 Fakultät für Biologie, Universität Konstanz, 78434 Konstanz, Germany
(Received 5 November 1993, revised 7 January 1994, accepted 18 February 1994)
Abstract
The orientation in external electric fields of rod-like fd-virus particles (length
nm, diameter
d = 9 nm) in aqueous suspensions is examined by the electric birefringence method. In aqueous suspensions the negatively charged
fd-particles are surrounded by a diffuse Debye cloud of counterions, which is characterized by the Debye-Hückel parameter
. A special experimental set-up is used to vary the ionic strength of the suspension, i.e. the Debye-Hückel parameter, and
therefore the electrostatic interparticle interaction. The birefringence signal
is measured as a function of the strength and frequency of the applied electric field in suspensions of very low ionic strength
(10
M-10
M). At low field strengths Kerr-behaviour is found. From the dependence of the electric anisotropy
on the Debye-Hückel parameter
it is concluded that the orientation of the fd-particles is correlated to an induced dipole due to a deformation of the diffuse
Debye cloud. Saturation electric birefringence values are far from that theoretically expected. This can be interpreted as
a destruction of the diffuse Debye cloud at high electric fields. At low field strengths the frequency dispersion below 1
kHz of
of the electrostatically interacting fd-virus suspensions shows anomalous behaviour. This negative electro-optic effect is
an evidence for the orientation of the particle's long symmetry axis perpendicular to the applied electric field. The dispersion
has a positive maximum at about 2 kHz. This maximum could be explained by different frequency dependencies of the electric
polarizabilities parallel and perpendicular to the long symmetry axis of the fd-rods.
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