Structures and Dynamics of Glass-Forming Colloidal Liquids under Spherical Confinement

Abstract

Recent theories predict that when a supercooled liquid approaches the glass transition, particle clusters with a special "amorphous order" nucleate within the liquid, which lead to static correlations dictating the dramatic slowdown of liquid relaxation. The prediction, however, has yet to be verified in 3D experiments. Here, we design a colloidal system, where particles are confined inside spherical cavities with an amorphous layer of particles pinned at the boundary. Using this novel system, we capture the amorphous-order particle clusters and demonstrate the development of a static correlation. Moreover, by investigating the dynamics of spherically confined samples, we reveal a profound influence of the static correlation on the relaxation of colloidal liquids. In analogy to glassforming liquids with randomly pinned particles, we propose a simple relation for the change of the configurational entropy of confined colloidal liquids, which quantitatively explains our experimental findings and illustrates a divergent static length scale during the colloidal glass transition.PACS numbers: 64.70.kj, 82.70.Dd, 61.20.Ne Understanding the nature of the glass transition is one of the most challenging problems in condensed matter physics [1][2][3][4]. Although ubiquitous and technically important, glasses still elude a universally accepted theoretical description. A molecular glass forms when the temperature of a liquid is quenched below its glass transition temperature T g . Near the transition, the relaxation of a liquid can slow down by many orders of magnitude with only a modest decrease of temperature by a factor of 2 or 3. The classical thermodynamic theory of Adam and Gibbs suggests that such a super-Arrhenius temperature dependence arises from cooperative particle rearrangements in localized regions that are related to the configurational entropy of supercooled liquids [5,6].To illustrate the static correlations associated with these localized regions, "point-to-set" correlations have recently been proposed in the framework of the random first-order transition theory (RFOT) [7][8][9][10][11], which is a modern development of the Adam-Gibbs theory unifying physical insights from the mode coupling theory and the spin glass theory [1,2]. In the RFOT, a gedankenexperiment was conceived [8], where particles outside a cavity of radius R in a supercooled liquid are suddenly frozen while the particles inside the cavity are allowed to freely evolve. The point-to-set correlation length, ξ, is defined as the minimal R such that the particles at the center of cavity are not affected by the pinning field imposed by the boundary. A cavity with R < ξ constrains the system into a local minimum of the free-energy landscape and captures an "amorphous order" particle configuration nucleated within the liquid. Nevertheless, important questions remain unanswered. First, it is still an open question if and how the static correlation develops in 3D experimental systems similar to the gedankenexperiment. Second, recent theory has su...

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