Science / Technology - Colloquium
Monday, March 5, 2007
4:00 PM-5:00 PM
Olin Hall
107
Self-assembly of colloidal particles and molecules into ordered structures is a fascinating phenomenon of both fundamental and applied interest. This lecture will demonstrate that the self-assembly phenomena in elastic liquid crystal (LC) media are particularly rich and can be controlled. In LCs the embedded spherical particles can cause elastic distortions of either dipolar or quadrupolar symmetry because of the anisotropic molecular interactions at the colloid-LC interfaces. I will show that the surface treatment of the colloidal particles and the LC confinement determine the nature of inter-particle interactions as well as the formation of colloidal structures. For example, the particles with the dipolar elastic distortions interact similar to the electrostatic dipoles and form chains along the far-field LC director. The particles with tangential surface anchoring and quadrupolar elastic distortions aggregate into chains directed at about 30 degrees to the average orientation of the LC molecules far from the spheres. When the elasticity-mediated colloidal interactions between particles take place at the surfaces of anisotropic fluids, the particle arrangements strongly depend on the boundary conditions at the confining surfaces and can vary from linear chains to hexagonal colloidal structures. Moreover, both in the LC bulk and at the surfaces, the inter-particle interactions and the structures are strongly altered by adding tiny amounts of chiral additives, resulting in twisted colloidal chains and spirals. I will show that even live biological cells (such as Pseudomonas aeruginosa) can be orientationally ordered when placed into the elastic liquid-crystalline matrices of DNA biopolymers. The particle motions are monitored using video-rate optical imaging and the interactions are explored using laser tweezers. The inter-particle colloidal forces exhibit rich angular and distance dependencies, consistent with the symmetry of the elastic distortions around the particles. The experimental observations are modeled considering the LC elastic properties and correctly reproduce the experimentally measured parameters. These findings impinge broadly on understanding of phenomena as diverse as colloidal interactions in anisotropic media and biofilm formation in the presence of extracellular biopolymers, as well as demonstrate the possibility of controlled colloidal self-assembly into tunable photonic crystal structures.
Cost: FREE
Sponsored by: WPI Physics Department, Dr. Stephen Jasperson
Suggested Audiences: College
E-mail:
snj@wpi.edu
Phone: 508-949-0782
Last Modified: February 12, 2007 at 12:46 PM
Powered by the Social Web - Bringing people together through Events, Places, & Common Interests