Particle assembly on patterned surfaces bearing circular (Dots) and rectangular (Stripes) surface features

Irreversible and localized adsorption of spherical particles on surface features of various shapes (collectors) was studied using the random sequential adsorption (RSA) model. Collectors in the form of dots and rectangles were considered, including the two limiting cases of squares and stripes. Numerical simulation of the Monte Carlo type enabled one to determine particle configurations, average coverage of particles, and the distribution for various collector length to particle size ratios (L) over bar = L/d and collector width to particle size ratios (b) over bar = b/d. It was predicted that particle coverage under the jamming state was highly nonuniform, exhibiting a maximum at the center and at the periphery of the collectors. The averaged number of particles < N-P > adsorbed at the jamming state was also determined as a function of the (L) over tilde and (b) over tilde parameters, as well as the averaged number of particles per unit length in the case of stripes. It was revealed that < N-P > was the highest for the circular and square collectors (for a fixed value of (L) over bar). On the other hand, for (L) over bar > 5, our numerical results could be well approximated by the analytical expressions < N-p > = theta(infinity)(L) over bar (2) for circles, < N-p > = 4 theta(infinity)(L) over bar (2)/pi for squares, < N-P > = 4 theta(infinity)(b) over bar/pi for rectangles, and < N-p > = 4 theta(infinity)(b) over bar/pi for stripes (per unit length). It was demonstrated that the theoretical results are in agreement with experimental data obtained for latex particles adsorbing on patterned surfaces obtained by a polymer-on-polymer stamping technique of gold covered silicon and on photolitographically patterned silane layers on silica.