Transition from One State to Another Is Quite Complex
Scientists say new discoveries about phase change require revised thinking about one of the basic building blocks of science and the way students are taught about some basic principles of the behavior of matter.
Researchers at Princeton University, Peking University and New York University examined phase change—the transition of matter from one state to another—at the molecular level and discovered it was far more complex than has previously been known. Their study appears in the journal Science. An NYU press release explains that when researchers used computers to look at metal changing from a solid to a liquid state, they found a complex process in which change can follow multiple pathways. Mark Tuckerman, a professor of chemistry and applied mathematics at NYU and one of the study's co-authors said that is contrary to previous understandings. "This means the simple theories about phase transitions that we teach in classes are just not right," he said.
The study shows change happens on multiple and competing pathways and involves at least two steps. In a first step, local defects occur on one pathway at a single lattice point in a crystalline solid. In a second step, these defects, which are very mobile, randomly migrate and can form large, "disordered defect clusters." Tuckerman says these clusters grow from the outside in, rather than from the inside out as was previously thought, and over time become large enough to cause transition from solid to liquid. On a different pathway, the defects grow into a thin line of disorder called "dislocations," which also eventually cause transition from solid to liquid. The research, arising from a ten year study of complex behavior in complex systems, is also described in Science Daily and R&D Magazine.