Kazem Edmond, Ph.D.

Soft Matter Research Scientist

Self-assembling chains — 2011-2014

We self-assemble flexible chains of bowl-shaped colloidal particles using the depletion interaction. With a rheometer, we study the bulk rheology of suspensions of these solutions. Under shear, the chains stretch, break, and reform, much like worm-like micelles, producing a rich variety of rheological behavior. We anticipate that these novel colloidal materials could provide insight into the rheology of worm-like micellar materials.

Rotational diffusion — 2007-2012

As a liquid approaches its glass transition, the fundamental nature of molecular diffusion changes. While both translational and rotational diffusion slow, spectroscopy experiments with molecular glass-forming materials have determined that rotational diffusion can slow at a far greater rate than translational diffusion. To directly observe this behavior, we dispersed fluorescently labeled tetrahedral clusters of microspheres in suspensions of colloidal spheres [1][2]. The clusters serve as tracers of rotational and translational diffusion, which we tracked simultaneously using confocal microscopy and a unique tracking algorithm [3]. Our colloidal system effectively models behavior seen in molecular materials [4]. The work was done in collaboration with Mark T. Elsesser, Gary L. Hunter, David J. Pine, and Eric R. Weeks.

[1] M.T. Elsesser, A.D. Hollingsworth, K.V. Edmond, D.J. Pine, Langmuir 27 (2010)
[2] K.V. Edmond, H.J. Park, M.T. Elsesser, G.L. Hunter, D.J. Pine, E.R. Weeks, Chaos: An Interdisciplinary Journal of Nonlinear Science 21 (2011)
[3]G.L. Hunter, K.V. Edmond, M.T. Elsesser, E.R. Weeks, Optics Express 19 (2010)
[4] K.V. Edmond, M.T. Elsesser, G.L. Hunter, D.J. Pine, E.R. Weeks, Proceedings of the National Academy of Sciences 109 (2012)
The confinement effect — 2006-2014

Using confocal microscopy, we watch the motion of colloidal particles as they mimic the behavior of a glassy substance. We have found that the motion of our particles are slower when confined, thus producing glassy behavior in a sample that would otherwise be a liquid in an unconfined geometry. In a way, we're controlling or triggering the glass transition by confining our samples to smaller volumes.

[1] C.R. Nugent, K.V. Edmond, H.N. Patel, E.R. Weeks, Physical Review Letters 99 (2007), pp. 025702-025702
[2] K.V. Edmond, C.R. Nugent, E.R. Weeks, The European Physical Journal - Special Topics 189 (2010)
[3] K.V. Edmond, C.R. Nugent, E.R. Weeks, Physical Review E 85 (2012)
Self-assembling cylinders — 2003-2005

Using hydrodynamic flow-focusing, we demonstrate the formation of long-lived cylindrical jets of an aqueous viscoelastic fluid. The jetting fluid, polyacrylamide in water, is driven coaxially within a stream of immiscible oil that subjects it to a strong extensional flow. Using high flow rates, we can adjust the diameter of the jets to between 4 and 90 μm while achieving several centimeters in length. As a proof of principle, we use the jet's liquid-liquid interface as a template for the self-assembly of microspheres into novel rigid and hollow cylinders.

[1] K.V. Edmond, A.B. Schofield, M. Marquez, J.P. Rothstein, A.D. Dinsmore, Langmuir 22 (2006)