Event
ChBE Seminar Series: Orlin Velev
Friday, October 25, 2013
10:00 a.m.-11:00 a.m.
Room 2108, Chemical and Nuclear Enginering Bldg.
Professor Jeffery Klauda
jbklauda@umd.edu
Principles and Engineering of Complex Particles that Interact, Assemble and Self-Propel in Programmed Patterns
Orlin Velev
INVISTA Professor
Department of Chemical and Biomolecular Engineering
North Carolina State University
The design of self-assembling and self-motile particles brings forth a number of fascinating scientific and applied problems. This talk will discuss how external AC fields can assemble asymmetric particles into structures with programmable symmetry and how local field gradients can make complex particles move and perform various functions. Directional polarization interactions drive the assembly of metallodielectric Janus particles into new types of staggered chains and anisotropic crystals. Patchy metallodielectric particles in AC fields form networks and crystals of unusual symmetry by quadrupolar and hexapolar interactions. A new class of permanently bound linear structures was recently field-assembled from binary mixtures of microspheres of opposite charge with strongly attractive interactions. We derive assembly rules for these structures based on the size ratio and number ratio of the two types of particles. The second part of the talk will cover our progress in designing physical mechanisms of making self-propelling particles, and identifying areas of their practical use. External AC electrical fields can be used as means of providing energy, propelling and steering Janus metallo-dielectric spheres and miniature semiconductor diodes that move, correspondingly, by particle-localized AC and DC electrohydrodynamics. We demonstrate how the diode particles can be steered via the symmetry of the AC field and hypothesize how an additional level of engineering can turn them into self-propelling microdevices. We will also present a new class of gel-based self-propelling particles moving on water surface by Marangoni effect. They are driven by a hydrogel reservoir releasing an ethanol flux that is cyclically disrupted by the bulk flows around the particles. Interpretation of the role of ethanol mass-transfer enabled us to design particles that dance in pre-programmed trajectories of translational and rotational steps. Finally, we will discuss how similar self-propelling floaters may serve as a new tool for environmental remediation.
