Sep 10, 2015
UCLA Professor Thomas Mason
Experiments by UCLA Professor Thomas Mason and former UCLA postdoctoral researcher Kun Zhao, PhD, have revealed a new mechanism for glass formation.
 
Prof. Mason and Dr. Kun Zhao, a former postdoctoral researcher in Prof. Mason's group who is now an assistant professor at Tianjin University in China, have created the first experimental realization of a colloidal glass in which the shape of the constituent particles has been designed to cause highly diverse local polymorphism, which in turn leads to geometrical frustration and the suppression of crystallization even when the colloidal particles are compressed very slowly. This discovery was made in Prof. Mason's UCLA laboratory.
 
The research was published in the Proceedings of the National Academy of Sciences U.S.A. on September 9, 2015, in a paper titled “Shape-designed frustration by local polymorphism in a near-equilibrium colloidal glass”.
 
The special shape-designed kites shown above can be locally packed into many different few-particle configurations: 5-kite configurations, such as the pentagonal star (green), frustrate the ordering of kites into large space-filling crystals of the alternating stripe 4-kite configuration (red). The wide variety of local configurations and their incommensurate nature effectively hide the crystal phase (like a needle in a haystack) and prevent large crystals from forming. The background image is a colored micrograph showing a disordered glass of randomly oriented kites (colors correspond to pointing directions of kites); a ring-like scattering pattern of a dense system of kites several different local configurations are also shown. Experiments are performed by slowly compressing a 2D system of kites (dispersed in water) in a tilted optical cell and using an optical microscope to record movies that reveal the structure and dynamics of the microscopic plate-like kite particles.  Image credit: Thomas G. Mason, UCLA.
 
Understanding the origin of disorder in glassy material is one of the most important unresolved questions in physical science. Sometimes glasses are formed by rapid, out-of-equilibrium quenching of the density that causes small-scale components, such as molecules or particles, to jam into disordered configurations. Other mechanisms that lead to glassy materials include entanglement of long chain-like polymer molecules and strong anisotropic attractions between components. Going beyond these existing types of glassy materials, scientists at UCLA have created and studied the first shape-designed colloidal glass of hard microscopic particles. By designing and lithographically printing many identical microscopic copies of a particular kite shape, they have created a two-dimensional Brownian system of mobile kites, and have shown that this system robustly forms a disordered glass when very slowly compressed, even when it could potentially self-organize into a crystal. They have revealed that the glassy disorder results from a high diversity of different local configurations of kites that frustrates crystallization. This new mechanism of near-equilibrium glass formation by shape-designed frustration can be broadly applied to shapes other than kites, and it provides new insights into the role of entropy and disorder in glassy materials.
 
Prof. Mason is a professor of physical chemistry and of physics at UCLA and leads an interdisciplinary research group in self-assembled soft matter, nanoemulsions, and microrheology.
 
For more information about Prof. Mason’s research visit his homepage.
 
Learn more about Prof. Mason’s research projects in the following UCLA Newsroom articles: