Jan. 30, 2007 — Dishwashing soap could become a thing of the past. Researchers have found a quick and inexpensive way to structure plastic so that it mimics the properties of the lotus leaf, which has a remarkable nonstick surface.
The technique not only creates a self-cleaning, water repellent surface — for a range of applications from frost-free glass and boat hulls to solar energy panels — it also produces microscopic air pockets in the surface of the material, making it silky smooth to the touch.
"You have less contact with the plastic and more with air, so the material feels like silk," said Ph.D. student Max Groenendijk of the University of Twente in The Netherlands.
Mimicking the self-cleaning lotus leaf is the goal of a few research labs around the world. The leaf has millions of microscopic pillars and a waxy surface that repels water droplets and encourages them to pool into bigger drops.
Once heavy enough, the drops roll off the surface, taking particles of dirt with them. A clean leaf soaks up more life-sustaining sunlight in the competitive understory of the forest.
Various researcher labs have suggested different methods for mimicking the lotus leaf structure in materials. Many of the approaches, however, attempt to structure coatings that are later applied to a material. This requires several production steps, making the process labor-intensive, time-consuming and expensive.
Groenendijk and his team devised a method to create the structure directly into a material, in this case a mold, which can be used and reused to produce any size or shape of self-cleaning product.
The process uses a special high-speed laser, called a femtosecond laser. It shoots short bursts of high-energy light at one-millionth of a billionth of a second onto a steel surface. At that high speed, the laser has very little time to melt the metal or produce craters — a consequence common with other kinds of lasers.
With one burst, the femtosecond laser vaporizes a tiny spot about half the diameter of a human hair, and some billionth of a meter deep. By applying more pulses, Groenendijk can create deeper holes and by careful arrangement of millions of laser bursts, he can write the bumpy structure of a lotus leaf into the metal mold.
