Tong Lin and colleagues explain that a method called “layer-by-layer” (LbL) self-assembly produces films and coatings for sensors, drug-delivery devices and many other products. LbL involves setting down alternate layers of positively and negatively charged materials that are held together by electric charges. With this approach, coatings can be custom-designed for specific applications by selecting the composition of each layer. The downside: These multilayer films are not very stable and eventually come apart. Lin and colleagues wanted to develop a way to stabilize those layers with UV light to form a “superhydrophobic” coating, one that uses natural surface forces to highly repel water and other materials.
Laboratory tests showed that the new coating, applied to cotton fabric, repelled water, acids, bases and organic solvents. The coating also was durable, remaining intact on the cotton fabric after 50 trips through a home washing machine. When the researchers applied several layers of the coating on the fabric, the contact angle (a measure of water-repellence) was about 154 degrees, making it even more repellent than car wax (90-degree contact angle), Teflon (95-degree contact angle) or products that repel rainwater from car windshields (110-degree contact angle).