Modeling of LbL multilayers with controlled thickness, roughness, and specific surface area

We present computer simulation results of the layer by layer self-assembling process of colloidal particles. We have generated five multilayer structures of monodisperse spherical particles according to a generalized model of random sequential adsorption of hard spheres. The multilayers, each created at a different single-layer surface coverage, are of similar thickness. We have compared the transparency of the five multilayers and the structure of their outer layers in terms of the two-dimensional pair-correlation function. We have analyzed the variation of multilayer thickness with the number of adsorbed layers. We have also calculated the root-mean-square roughness of the multilayers as a function of the number of adsorption cycles. Finally, we have determined the specific surface area of the porous films as a function of the distance from the solid substrate. Our results suggest that in the limit of low porosity the multilayer transparency decreases exponentially with its porosity. The multilayer thickness is directly proportional to the number of adsorption cycles. The average single-layer thickness grows asymptotically with the single-layer coverage. We have also found that with the number of adsorbed layers the multilayer roughness increases to an asymptotic value. We have observed oscillatory variations of the multilayer specific surface area, decaying exponentially with the distance from the substrate. The decay length of the oscillation increases exponentially with the surface coverage. We have also determined the particle layer interpenetration for each multilayer and we have found that it decreases exponentially with the increase of the coverage. Our results suggest that all the film characteristics strongly depend on the method of its preparation and can be controlled by manipulating the single-layer surface coverage or deposition time. The results can be useful for efficient designing multilayers with desired properties.