In static friction, chemistry is key to stronger bonds

Inspired by phenomena common to both earthquakes and atomic force microscopy, materials engineers have learned that chemical reactions between two silicon dioxide surfaces cause the bonds at that interface to "age," or strengthen gradually over time. In researchers' understanding of static friction, it's an advance with staying power. "What happens is that when you form one bond across the interface, it actually affects the local environment and makes it harder for other bonds to form," says Izabela Szlufarska , a UW-Madison associate professor of materials science and engineering. "As a result, the process slows down in a very specific way — logarithmically — and that happens in materials such as silica that have strong directional bonding." Silicon dioxide, or silica, is abundant in the Earth's crust and is of great importance for the semiconductor industry. Relevant in several fields in which humidity is a factor, the advance could, for example, enable manufacturers to fine-tune semiconductor wafer bonding processes or help geologists better understand the conditions under which tectonic plates slide and earthquakes occur. "The mechanism we discovered is possible because there are chemical reactions at the interface enabled by water," says Szlufarska. Friction is the force that resists motion, or sliding, between surfaces that touch.