Friday, January 14, 2011

How liquids behave

How liquids behave: Liquids have long been known to exhibit a rapid change in properties near a point called the glass transition temperature, where the viscosity of the liquid — its “thickness,” or resistance to flow — becomes very large. But MIT professor Sow-Hsin Chen and his co-researchers have found a different transition point at a temperature about 20 to 30 percent higher, which they call the dynamic crossover temperature. This temperature may be at least as important as the glass transition temperature, and the viscosity at the dynamic crossover temperature seems to have a universal value for a large class of liquids (called glass-forming liquids) that includes such familiar substances as water, ammonia and benzene.

At this new transition temperature, “all the transport properties of the liquid state change drastically,” Chen says. “Nobody realized this universal property of liquids before.”

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