The angular distribution function of rodlike particles in Langmuir-Blodgett (LB) films is numerically analyzed. The calculation is based on the integral form of the rotatory diffusion equation and, in contrast with previous analyses, does not assume an instantaneous thermal equilibrium. As each particle keeps memory of the flow history on the water surface, the final distribution function is dependent on the initial conditions of the particle. However, when the initial point is so far from the substrate that the memory of initial point is almost lost, the final distribution function is approximately determined by the dimensionless number C=(ζ'G+τ0)/2kBT, where ζ' is the rotational friction coefficient, τ0 the Bingham yield value, a the substrate width, and vd the dipping velocity of the substrate. The presence of a meniscus region around the substrate should be taken into account. The streamlines between the water surface and the substrate surface are smoothly connected, while assuming a cylindrical shape for the meniscus. The angular distribution function obtained by this numerical calculation is in good agreement with the experimental results for a mixed LB system of merocyanine dye/fatty acid.
ASJC Scopus subject areas
- Physics and Astronomy(all)