Fabrication of superhydrophobic surfaces from mixtures of aluminum distearate and fatty acids via intermediate organogel formation

Superhydrophobic surfaces were obtained easily from the mixtures of aluminum distearate (AlDS) and typical saturated fatty acids with long alkyl chains by a casting method. In contrast to a mediocre water contact angle of 109 +/- 1A degrees for the surface obtained from only AlDS, the mixture of AlDS and stearic acid (SA) gave a superhydrophobic surface having the contact angle of 164 A +/- 2A degrees and the sliding angle of 3 A +/- 1A degrees at the SA/AlDS weight ratio of 12. A homogeneous surface was not available from only SA on a macroscopic scale. To be superhydrophobic, the surface needs to take a hierarchical structure, like a table coral which consists of several tens of micrometer-size primary structure of widely branched SA crystals. In this study, the hierarchical structures were obtained by crystallizing fatty acids in the organogel composed of AlDS and a solvent, to avoid the formation of needle-like or plate-like bulky crystals as usually seen in the recrystallization of fatty acids.