J. Phys. Chem. 1994,98, 364-368
364
Electrokinetic Properties of Aqueous Suspensions of Interacting Rodlike Tobacco Mosaic Viruses in the Gas- and Liquidlike Phase Martin Deggelmamt Christian Craf, Martin Hagenbiichle, Udo HOW,Christian Johner, Hansgerd Kramer, Christoph Martin, and Reinhart Weber' Universitirt Konstanz, Fakultiit fur Physik, 78464 Konstanz, Federal Republic of Germany Received: August 27, 1993'
Electrophoretic mobility and conductivity data of aqueous suspensions of rodlike tobacco mosaic virus (TMV) (length 1 = 300 nm, diameter 2u = 18 nm) are presented in a wide range of particle concentration, below and above the overlap concentration c* = 1 particle/length3. The mobility is investigated in relation to the small ion concentration down to salt-free suspensions. At low small ion concentration a screened Coulomb interaction between the particles appears, i.e., the double layers surrounding the particles begin to overlap. This leads to a decrease of the mobility of TMV particles. Another effect which influences the particle mobility is the change in the dissociation degree of the weak surface groups on the particles which are responsible for the particle charge. It is investigated to what extent potential and particle charge can be determined by means of the standard theories.
Introduction Aqueous suspensions of tobacco mosaic virus (TMV) are good model systems to study the static and dynamic properties of rodlike colloidalparticles.192 TMV has a length of 300 nm and a diameter of 18 nm. On its surface there are acidic and alkaline groups which lead to a negative net charge of the macromolecule when it is suspended in water. Therefore the particle is surrounded by an ionic atmosphere which is usually separated into two layers.3 The inner part of this double layer, the Stern layer, consists of adsorbed ions which are fixed on the particle surface. The outer part is the diffuse layer where the small ions are moving freely. Between the particles there exists a screened Coulomb interaction depending on the particle and the small ion concentration. The mean particle distance is given by their concentration. Increasing the particle concentration leads to an increase of the interaction. The small ions screen the electrostatic interaction. Increasing their concentration lowers the interaction. For suspensionsof rodlike particles it is useful to introduce the overlap concentration c* defined as one rod per cubic particle length. At very low concentration (c
