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 Ñ its Òthickness,Ó or resistance to flow Ñ 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, Òall the transport properties of the liquid state change drastically,Ó Chen says. ÒNobody realized this universal property of liquids before.Ó The work, carried out by physics professor Francesco Mallamace of the University of Messina, Italy (who is a research affiliate at MIT) and four of his students from Messina, along with Chen, an MIT professor emeritus of nuclear science and engineering, and Eugene Stanley, a physics professor at Boston University, was published on Dec. 28 in the Proceedings of the National Academy of Sciences.

This is very basic research and Chen says it is too early to predict what practical applications this knowledge could produce. ÒWe can only speculate,Ó he says, because Òthis is so new that real practical applications havenÕt really surfaced.Ó But he points out that one of the most widely used building materials in the world, concrete, flows as a liquid-like cement paste during construction, and a better ability to understand its process of transition to solid form might be significant for improving its durability or other characteristics.