Introduction: Superhydrophobic Surfaces Based on PDMS Microstructures

By www.gc-a.net

Super–hydrophobic surfaces

The aim of this project is to study super-hydrophobic surfaces and their behavior.

Super-hydrophobic surfaces (SHS) are surfaces which result in contact angles of water on theses surfaces of greater than 150° in conjunction with shallow sliding angles, α. [1]

SHS are very useful and their applications span a broad range including such diverse applications as in the aerospace industry where they are used to minimize aerodynamic drag or keep the aerodynamic surfaces ice free and the medical industry where they are used on/in artificial, insertables for minimization of the clotting cascade or fouling.

Super-hydrophobic materials rely on a composite interface of different contact angles as demonstrated by Cassie's law; essentially, all things been equal, a rougher surface allows for a much higher apparent contact angle than one that has the same composition but a smoother surface.

In nature, this behavior is often describe as Lotus effect, and it is use by plants for self cleaning purpose, and in case of carnivorous plants, feeding.

In order to create these type of surface structures, we will create 4 different masks (they can be all be on the same substrate). The masks will be a square array of square features. The size of the features and the lattice constant will be varied for each mask. We expect the characteristic dimensions to be in the range of 10 to 500 microns. Using the mask set and varying the height of the etched features (through etching or starting thickness) will allow for a small set of molds for soft lithographic patterning in PDMS surfaces. Another dimension will be added to this matrix in that chemical, such as 1H,1H,2H,2H-perfluorooctyl treatment, or plasma (oxygen) of the PDMS creating a four dimensional test. Because of the large ensuing matrix size, we shall probably employ an optimized DEO (design of experiment.)

In the experiment, the effective contact angle, the sliding angle and the velocity of shedding will be analyzed.