Electric birefringence measurements in aqueous fd virus solutions

Abstract

Aqueous solutions of rodlike fd virus particles (length l = 880 nm, diameter d = 9nm) are examined by the transient electric birefringence method. A special experimental setup is used, which allows a very sensitive variation of the screened Coulomb interaction between the particles. The birefringence signal is measured as a function of the virus particle concentration and the ionic strength of the solution. For low applied electric field strength it is demonstrated that anomalous birefringence is an effect of the steric and electrostatic interactions between the fd virus particles. It is shown that this behavior is correlated to a decrease of the rotational diffusion constant Dr. In the case of high ionic strength the deduced values of Dr are in agreement with the theory of Teraoka and Hayakawa1 up to a concentration of 8c* (c* = 1 particle/ length3 is the overlap concentration); at larger concentrations the values are significantly higher than predicted.

Statics and dynamics of strongly charged soft matter

“…The average orientation of a variety of charged rod-like particles (such as Tobacco-Mosaic [244] and FD viruses [245], or different synthetic polyelectrolytes [246]) in electric fields has been determined in birefringence experiments. The anisotropic electric polarizability favors an orientation with the direction of the maximal polarizability parallel to the electric field, as seen in Fig.24.…”

“…This is called the normal birefringence of charged rods. Anomalous birefringence, meaning perpendicular orientation of rods, is typically obtained for long particles, low salt concentration or particle concentrations beyond mutual overlap [246,245,248] and at present only partially understood [249]. It seems likely that the anomalous electric birefringence of charged polymers is caused by the above-mentioned hydrodynamic orientation in cases when the typically much stronger electric polarizability orientation is weakened due to the overlap or evaporation of counterion clouds.…”

Electrooptics of β-FeOOH Particles in Aqueous Media

“…Thus, the sign of the optical anisotropy factor, g/n, in Eq. [4] should be positive. An unusual concentration dependence is noticed in Fig.…”

“…The electrooptic quantities are quite important from the fundamental and practical points of view because they are directly related to the stability of the dispersed colloidal systems at low and high concentrations. In addition to latexes (10), viruses (4,11), and DNA (8), both EB and ELS studies have lately been carried out on optically more complex systems, such as alumina (Al 2 O 3 ) (12), α-and β-FeOOH (13,14), and palygorskite (15), at higher concentrations, where both electrostatic interaction and multiple light scattering are involved (16). The orientation mechanism of those colloid particles by the applied external electric field is of primary importance to understand the surface properties and the bulk electrooptical behavior in aqueous media.…”

Hydrodynamic effects in driven soft matter

“…As will be discussed, the selection of these topics is closely related to novel emerging experimental techniques and activities. Example i) is related to the effect of anomalous birefringence, which is observed in experiments involving charged rod-like particles such as Tobacco-Mosaic [8], FD viruses [9] or synthetic polyelectrolytes [10,11] and cylindrical micelles [12] in electric fields. Normally, charged objects in electric fields orient parallel to an externally applied electric field due to the anisotropic polarizability which is mostly caused by the easily displaceable counterion cloud.…”