Process changes texture of plastics on demand

By applying specific voltages, the team has also shown that it can achieve this control over large and curved surface areas. "By changing the voltage applied to the polymer, we can alter the surface from bumpy to smooth and back again," said Xuanhe Zhao, assistant professor of mechanical engineering and materials science at Duke's Pratt School of Engineering. "There are many instances, for example, when you'd want to be able to change at will a surface from one that is rough to slippery and back again." Scientists have long been able to create different patterns or textures on plastics through a process known as electrostatic lithography, in which patterns are etched onto a surface from an electrode located above the polymer. However, once the patterns have been created by this method, they are set permanently. "We invented a method which is capable of dynamically generating a rich variety of patterns with various shapes and sizes on large areas of soft plastics or polymers," Zhao explained. "This new approach can dynamically switch polymer surfaces among various patterns ranging from dots, segments, lines to circles. The switching is also very fast, within milliseconds, and the pattern sizes can be tuned from millimeter to sub-micrometer." The findings follow Zhao's earlier studies, which for the first time captured how polymers react to changing voltages. Those experiments showed that as the voltage increases, polymers tend to start creasing, finally leading to large craters. This explained in physical terms, for example, why polymers used to insulate electric wires tend to fail over time. The new lithography strategy takes useful insights from this failure mechanism. Potential usages for the new method include creating surfaces that are self-cleaning and water repellant, or even as platforms for controlled-release drug eluting devices.