Droplet size assisted polysiloxane architecting

Abstract

(Super)antiwetting shielding around engineering materials and protecting them against harsh environmental conditions has been achieved in recent years via growing various geometry polysiloxane (or silicone) patterns around them by using droplet assisted growth (DAGS) method, where the polymerization takes place inside of the water droplets acting as reaction vessels. The size and distribution of these reaction vessels are the main factors in making different geometry silicone patterns; however, very little is known about the fate of these droplets throughout the polymerization. Here, we proposed keeping the relative humidity (% RH) inside the reactor stable throughout the polymerization as a new coating parameter to force the size of the reaction vessel water droplets to be the same for building simple shape silicone rods with controlled geometry and distribution. In this manner, we grew simple geometry cylindric micro-rods on surfaces and could tune their length, diameter, inter-rod spacings, and thus the (super)hydrophobicity. Beyond fabricating simple geometry cylindrical micro rods, here, we also demonstrate that by changing the amplitude and the stability of the % RH, it is possible to fabricate different (super)hydrophobic nano-grasses, conical silicone micro-rods, and isotropic silicone nanofilaments (SNF). In the end, the proposed new way of tuning initial and in-situ reaction vessel droplet size can be used as a single factor to formulate different geometry silicone patterns with tunable dimensions, leading to different roughness and thus different degrees of hydrophobicity and superhydrophobicity. Due to its simplicity, silicone patterning with irregular spacing and size is preferred among other coating techniques, but the mathematical description of these irregular patterns is not trivial to explain their (super)hydrophobicity. To a certain extent, the droplet-size-assisted silicone shaping in this work provides a new way to control the length, diameter, morphology, inter-rod spacing, and thus the (super)hydrophobicity of the silicone patterns, especially those in the shape of simple cylindrical micro-rods. This control over silicone architecting will help to prepare new (super)hydrophobic coatings with more controlled morphology and thus wettability; on the other hand, it will support surface scientists modeling the connection between surface geometry and (super)antiwetting of such irregular pillared surfaces that remain elusive.