Confinement of two-dimensional (2D) colloidal systems in the lateral directions can cause important changes in the properties of the system. Likewise, the relaxation of strictly 2D colloidal systems to quasi-2D confinement can induce drastic changes in structure. Of particular interest is the structure of self-assembled magnetorheological (MR) fluids confined in the thin-slit geometry. This system is of interest from both a fundamental science standpoint as a model for the effects of confinement on self-assembly as well as for practical applications indicated by the increasing exploitation of self-assembly for microfluidic applications. Self-assembled MR fluids have been used as structural components in microfluidic systems offering a fast, inexpensive alternative to traditional photolithographic techniques. The characteristic length-scales in microfluidic devices have continued to shrink down to the colloidal size, making studies of self-assembly under extreme confinement a timely undertaking. It has become essential to study these systems in order to enable the design of meaningful applications using such technology.

My doctoral thesis focused upon the self-assembly of MR fluids in confined geometries. In order to study this problem, I developed a versatile Brownian dynamics (BD) code capable of simulating MR colloids of any shape interacting in any general geometry. I used the BD code to study the self assembly of spherical colloids confined in two-dimensional (2D) channels and discovered a number of interesting phenomena that were subsequently published (1,2). In addition to the simulation work, I performed an extensive set of experiments on the self-assembly of MR colloids in 2D microfluidic channels and showed the first experimental observation of re-entrant melting as a function of confining geometry (3). In addition to the 2D studies, I investigated the factors controlling self-assembly in the thin-slit geometry. I elucidated the important physical phenomena affecting the self-assembly of dilute MR fluids in this common microfluidic geometry. I showed how the system transitions from 2D to 3D behavior as the confinement is relaxed from a monolayer to a channel of finite thickness (4,5).

During the course of my Ph.D. I also completed a Masters of Chemical Engineering Practice in which I gained invaluable industrial experience. Since graduating, I took a position as a Lecturer of Chemical and Biological Engineering at Tufts University and spent the 2006-2007 academic year teaching graduate level Transport Phenomena, graduate level Thermodynamics, two undergraduate laboratory courses, and a graduate level course in microfluidic technology. This experience has enabled me to sharpen my teaching skills and given me a great head-start in my development as an academic researcher and teacher. In February of 2007, I was awarded the MIT/MGH postdoctoral fellowship in translational research (2 awards out of more than 50 applicants) and I am currently a postdoctoral fellow in the BioMEMS Resource Center at Massachusetts General Hospital.

(1) Haghgooie, R. and Doyle, P. S.; “Structural analysis of a dipole system in two-dimensional channels”, Phys. Rev. E, 70, 061408, (2004).

(2) Haghgooie, R. and Doyle, P. S.; “Structure and dynamics of repulsive magnetorheological colloids in two-dimensional channels”, Phys. Rev. E, 72, 011405, (2005).

(3) Haghgooie, R., Li, C., Doyle, P. S.; “Experimental study of structure and dynamics in a monolayer of paramagnetic colloids confined by parallel hard walls”, Langmuir, 22, 3601, (2006).

(4) Haghgooie, R. and Doyle, P. S.; “MR fluid structure in quasi-2D”, Europhys. Lett., 77, 18002, (2007).

(5) Haghgooie, R. and Doyle, P. S.; “Transition from 2D to 3D behavior in the self-assembly of magnetorheological fluids confined in thin-slits”, Phys. Rev. E, (in press).