Levich Institute Seminar Announcement, 10/05/2004

Tuesday, 10/05/2004
2:00 PM
Steinman Hall, Room #312
(Chemical Engineering Conference Room)

Professor Mike Solomon
University of Michigan
Department of Chemical Engineering


"Confocal Microscopy, Light Scattering and Particle Shape Effects in Gels of Colloidal Rods"

ABSTRACT

Submicron colloids and nanoparticles are key building blocks for the assembly of functional structures in traditional industries such as paints and ceramics as well as in emerging areas such as sensing and photonics. Unfortunately, colloidal spheres yield a disappointingly short list of ordered structures by self-assembly, perhaps because of the high symmetry of building block shape and potential interactions. Shape anisotropy (anisometry) might expand possibilities for ordered colloidal assembly. For example, shape effects have been exploited at the molecular scale to yield a rich array of liquid crystal structures. Here we address the effect of anisometry on the structure and dynamics of colloidal suspensions. Of particular importance is gelation, a slowing down of dynamics in colloidal systems that competes with the assembly of ordered phases. To assess aspect ratio effects on gelation, aggregates and gels were formed from colloidal boehmite rods of approximately monodisperse dimensions and aspect ratios in the range 4-30. In static and dynamic light scattering studies, we found unexpected effects of particle shape on fractal structure and gel internal dynamics. To directly visualize colloidal rod assembly, we developed a model system of fluorescent poly(methyl methacrylate) ellipsoids prepared by extensional deformation of initially spherical colloids in an elastomeric film. Structures were assembled by sedimentation and directly visualized by confocal laser scanning microscopy (CLSM). The distribution of colloidal rod orientations was extracted from three-dimensional image volumes acquired by CLSM. The general possibility of applying shape anisotropy to assemble new kinds of oriented structures in colloidal systems is discussed.

BRIEF ACADEMIC/EMPLOYMENT HISTORY

Michael J. Solomon is associate professor of chemical engineering at the University of Michigan. He received his Ph.D. at the University of California at Berkeley in 1996. After a post-doctoral appointment at the University of Melbourne, Australia, he joined the University of Michigan as an assistant professor in 1997.

CURRENT RESEARCH

Solomon's current research interests are in colloidal assembly, suspension microhydrodynamics, rheology and polymer turbulent drag reduction.