Superabsorbent Capped Truncated Silica Microcone Arrays: Fabrication and Extended Laplace Pressure and Gibbs Free Energy Study

The ability of a surface to completely absorb a liquid droplet is an important property that can be controlled by geometrical structure and chemical composition of the surface. Here, using Laplace pressure and Gibbs free energy (GFE) considerations, a capped truncated microcone array geometry is proposed to obtain a near zero degree for contact angle (θ) of a water droplet. Our results showed that two essential conditions must be met to achieve a superabsorbent surface. First, negative Laplace pressure and, second, absence of a relative minimum in the plot of GFE versus contact angle. To investigate the effect of surface tension on the wettability, capped truncated microcone array films were prepared on Si (100) substrate using a lithography method. To validate the proposed geometry as a super water-absorbent surface, we compared theoretical calculations with the experimental results. Our theoretical and experimental studies show that the capped truncated SiO₂ microcone array film is a superabsorbent surface with nearly zero contact angle. The amount of 130° ± 3 was measured for the water contact angle of the capped truncated Si microcone array in the hydrophobic state, which is very close to the calculated water contact angle using the minimum of GFE (126.1°). Results proved that the predicted water contact angles are in very good agreement with the experimental measurements.