From a Landau theory the static scattering intensity distribution I(q) of microemulsions is obtained. As essential ingredient we have included a negative gradient term in the free energy expression. The form of I(q)∼(a2+c1q2+c2q4)−1 yields for a2>0, c1<0, and c2>0 a single broad scattering peak and a q−4 decay at large q, both properties experimentally observed for a variety of microemulsions containing comparable amounts of water and oil. The peak originates from the modulation in the corresponding space correlation function given by γ(r)=(d/2πr)⋅e−r/ξ⋅sin(2πr/d). It is shown that the scattering intensity relation describes experimental literature data remarkably well, using only three fit parameters.

General formulas are derived for the force and torque on a charged rigid macromolecule in electric fields. The theory is based on the Smoluchowski mean field approximation and yields the motion in terms of the electric potential and certain geometric quantities of the particle. If convection can be neglected in the ion conservation equations, the theory makes any further hydrodynamic considerations unnecessary. The formulas of Smoluchowski, Hückel, and Henry for electrophoretic mobility are obtained as simple consequences. Smoluchowski’s formula is generalized to nonconstant surface potentials. The torque on an uncharged rod in moderately strong field is considered.

PACS. 05.40 -Fluctuation phenomena, random processes, and Brownian motion. PACS. 68.10 -Fluid surfaces and interfaces with fluids (inc. surface tension, capillarity, PACS. 87.20C -General theory of interfaces (inc. practical models).wetting and related phenomena).

We investigate the effective conductivity (σe) of a class of amorphous media defined by the levelcut of a Gaussian random field. The three point solid-solid correlation function is derived and utilised in the evaluation of the Beran-Milton bounds. Simulations are used to calculate σe for a variety of fields and volume fractions at several different conductivity contrasts. Relatively large differences in σe are observed between the Gaussian media and the identical overlapping sphere model used previously as a 'model' amorphous medium. In contrast σe shows little variability between different Gaussian media. 05.40.+j, 72.15.Cz