Formation of multilayered structures in the layer by layer deposition of colloid particles

Theoretical calculations of particle film formation in the layer by layer (LbL) self-assembling processes have been performed according to the generalized random sequential adsorption (RSA) scheme. The first (precursor) layer was generated using the standard RSA scheme pertinent to homogeneous surface. Formation of the consecutive layers (up to twenty) was simulated for two kinds of particles of equal size. The interaction of two particles of different kind resulted in irreversible and localized adsorption upon contact, whereas particles of the same kind were assumed to interact via the hard potential (no adsorption possible). Using this algorithm particle coverage (2D density) and volume fraction (3D density) were calculated as well as the film thickness as a function of the number of layers. Additionally, the structure of the film was quantitatively characterized in terms of the 2D and 3D pair correlation functions. The simulations revealed that particle concentration distribution in the film was more uniform for low precursor layer density than for higher density, where well-defined layers of closely packed particles appeared. It was also predicted theoretically that the averaged value of particle volume fraction in the uniform film region was rho(LbL)=0.42, which is very close to the maximum packing density equal to 0.382 predicted from the 3D RSA model. On the other hand, the roughness of the film was the lowest at the highest precursor layer density. It was shown that for low precursor layer density the film thickness increased with the number of layers in a nonlinear way. However, for high precursor layer density, the film thickness increased linearly with the number of layers and the average layer thickness was close to the hexagonal layer thickness equal to 1.73a p. It was concluded that our theoretical results can be effectively exploited for interpretation of the LbL processes involving colloid particles and polyelectrolytes.