Morphology and stability of water condensation structures on a series of self-similar micropatterned substrates

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In this work, we report on the morphology and stability of water domains growing by condensation on flat chemically micropatterned substrates. The surface pattern consists of hydrophobic hexagonal domains that are distributed following a hexagonal lattice in a hydrophilic continuum. The size and spacing of the hexagons are varied from one sample to the other in such a way as to produce a series of self-similar surface patterns. The size and stability of the water condensation structures growing on these surfaces are investigated in relation to the pattern size and the chemical contrast between the wetted continuum and the non-wetted hydrophobic domains. The water structures that initially grow and spread over the hydrophilic continuum are found to be unstable, collapsing on the hydrophobic domains at a characteristic (normalized) size, which is shown to be independent of the patterns, for a given chemical contrast. This scale invariance of the condensation structures is discussed on the basis of the self-similar variation of the characteristic sizes of the patterns that drive their instability and collapse. Finally, we show that for a high enough chemical contrast, the condensation structure could be tuned into a stable continuum water film that surrounds “dry” spots of non-wetted hydrophobic hexagons.