Morphology and thermodynamics of a microdroplet deposited on a grooved inhomogeneous surface with triangular cross section of the grooves were studied by computer simulations with the use of Surface Evolver program. With increasing volume of the droplet, it initially spreads along the series of grooves assuming the filament-like morphology. After reaching a certain volume, the surface wetted by the droplet is reduced and the droplet assumes the bulge morphology or spreads over the surface bordering on the groove initially occupied (it can be either a neighboring groove or a flat surface). The character of the process is determined by the geometry of the edge of the inhomogeneity studied. The effect described also depends on the number of grooves G and the Young contact angle θY. The change in the shape of the droplet becomes more pronounced with decreasing θY and G. Above a certain number of grooves, in the range of contact angles studied (e.g., G > 6 if θY = 70° and G > 4 if θY = 75°), no morphological transition of the droplet was observed.

The behavior of a droplet deposited on solid surfaces, one in the shape of a narrow strip and the other in the shape of a groove of triangular cross-section, was studied. Surface/interface energy of the droplet on the surfaces was calculated. In addition, Laplace pressure and linear size of the droplet were determined. Unexpected dependence of the shape of the droplet placed on the triangular groove on its volume, that is, the jumpwise change in the droplet shape taking place on increasing of its volume, was revealed. This change was found to show some features of a second-order phase transition.

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A polymer molecule (represented by a statistical chain) end-grafted to a topologically rough surface was studied by static MC simulations. A modified self-avoiding walk on a cubic lattice was used to model the polymer in an athermal solution. Different statistical models of surface roughness were applied. Conformational entropies of chains attached to uncorrelated Gaussian, Brownian, and fractional Brownian surfaces were calculated. Results were compared with the predictions of a simple analytical model of a macromolecule end-grafted to a fractal surface.FigureVisualization of SAW generated by the (023) algorithm on a 3D cubic latticeElectronic supplementary materialThe online version of this article (doi:10.1007/s00894-012-1546-5) contains supplementary material, which is available to authorized users.

Abstract. The applicability of Wenzel's equation to describe a liquid droplet settled on the solid surface regularly patterned with rectangular prisms was examined by means of simulations of the droplet/surface system morphology and energetics. The droplet deposited on the meso-scale surface roughness (i.e. the droplet size was larger than the size of heterogeneities by about an order of magnitude) was considered. Several different approaches to the estimation of the contact angle were employed. The discrepancies between the results of simulated experimental measurements and the predictions based on the Wenzel equation were analyzed and discussed. The influence of three-phase contact line effects on the droplet morphology and the existence of metastable states was shown.