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Research Abstracts Online
January 2008 - March 2009

University of Minnesota Twin Cities
Institute of Technology
Department of Chemical Engineering and Materials Science

PI: Michael Tsapatsis

Evaporation-induced Assembly of Colloidal Crystals From Lysine-Silica Colloids

These researchers are studying the fundamentals of colloidal crystal assembly by an evaporation-assisted coating mechanism. A simplified model of the process based on an equivalent network concept was applied to the problem as a first step in elucidating the interplay of flow and structure in this highly complicated process. Equivalent network simulations suggested a simple criterion for stability of the crystal interface: uniform solvent flux near the interface induced by the geometry of the interfacial plane. Colloidal particle motion is considered to be dominated by convective forces, so that uniform particle fluxes follow directly from uniform solvent flux. Simulations of solvent flow through assembling colloidal structures provided insight into capillary pressure and flow rate distributions throughout a nascent crystal. The geometric interface between colloidal suspension and the assembling crystal was found to be the most important structural feature influencing microstructure propagation; in particular, a declining {311} facet was identified as a potentially stable crystal interface in the convective assembly process.

The outcome of previous work carried out at MSI was a proposed mechanism that may clarify details of the colloidal assembly process. Because the proposed mechanism is based on a pseudo-steady analysis, the researchers are refining our modeling approach via dynamic simulation. A variety of dynamic phenomena may be equally important to those we have identified, including particle restructuring at the interface; how strongly random thermal motion can influence particle trajectories as they approach the crystal interface; and the influence of mutual interparticle repulsion or adhesion by electrostatic and van der Waals forces. These aims will be pursued by means of the well-developed Brownian dynamics simulation methodology, including hydrodynamic interactions between particles.

Group Members

Nicole Atchison, Graduate Student
Damien Brewer, Graduate Student
Leon Cassidy, Undergraduate Student
Jungkuy Choi, Graduate Student
Sunho Choi, Graduate Student
Wei Fan, Visiting Researcher
Missy Gettel, Undergraduate Student
Sandeep Kumar, Graduate Student
J. Alex Lee, Graduate Student
Pyung-Soo Lee, Graduate Student
Sudeep Maheshwari, Graduate Student
Elizabeth Mallon, Graduate Student
Rajiv Ranjan, Graduate Student
Joshua Sheffel, Graduate Student
Mark Snyder, Visiting Researcher
Jared Stoeger, Graduate Student
Ana Torres, Graduate Student
Virany Yuwono, Undergraduate Student
Zhuopeng Wang, Visiting Researcher