Deen Group People


Department of Chemical Engineering
Room 66-463
Massachusetts Institute of Technology
77 Massachusetts Avenue
Cambridge, MA 02139-4307 USA

Telephone (617) 253-6490
Email:
pdecha@mit.edu,
dechadil@fas.harvard.edu




Panadda Dechadilok

Graduate Research Assistant

B.A., Physics and Applied Mathematics, Northwestern University, 2002

Research Interests

Hindered Diffusion and Convection in Pores of Well-defined Geometry

It is well known that solutes in liquid-filled pores of molecular dimensions have reduced diffusivities and are sieved during filtration. For solute molecules that are large enough to act as hydrodynamic particles, these phenomena can be explained by a combination of particle-wall hydrodynamic interactions and steric restrictions. To look at the hydrodynamic interactions alone, we know they depend on how close the particle is to the wall, and that they are therefore affected by any force that influences its position. Even if long-range (e.g., van der Waals or electrostatic) forces are negligible, the finite size of the solute restricts its access to the region near the wall and therefore affects its flux. So a precise explanation for the reduction of solute diffusivities is both complex and to date elusive. A reasonable model however will impact studies in microvascular permeability, membrane separation and microfluidic separation to name a few applications.

Theoretical expressions that include these mechanisms have been available for many years, but, even for spheres in pores of constant cross-section, sufficient hydrodynamic information has been lacking until recently. In particular, the local enhanced drag and local lag coefficient for off-axis positions had not been fully characterized. This difficiency has required that results for symmetrically positioned particles ("centerline approximations") be employed in predicting diffusional and convective hindrances. We have recently submitted a paper reviewing the current status of hindered transport theory for neutral spheres in long cylindrical pores or slits, and have shown that such approximations are no longer necessary. Comparisons in the paper have been made between the predictions and recent data obtained by tracking particle positions in microchannels.

Currently, we are investigating the effect of the electrical charge of the solute and the pore wall on the local hydrodynamic coefficients. Recent experimental work has demonstrated that it is possible to change the selectivity of membrane systems by exploiting long-ranged colloidal interactions between the solutes and membrane pore wall, both by changing the equilibrium partitioning coefficient, and the hydrodynamic hindrance factor inside the pores. There have been a number of theoretical analyses of the effects of electrostatic interactions on solute transport in membrane systems, most of which focused on evaluating the equilibrium partition coefficient for a charged solute in a narrow pore. No corresponding calculation has been made however to account for the effects of long-range electrostatic interactions on the hydrodynamic coefficients. Our plan is to calculate the impact of an electrostatic interaction between solutes and pore wall on these hydrodynamic transport coefficients for a charged particle inside a cylindrical pore. In particular, we are interested in the case of which the Debye length is finite, and want to find out how a deformation of an electrical double layer leads to a change in the local enhanced drag and the local lag coefficient, and confirm our results with a particle tracking experiment.

Personal Interests

I have been interested in fluid dynamics since entering graduate school and from the start was looking for research that would entail fluid dynamics in biological systems, but was uncertain what specific project type I would like to work on. By accident I came across Analysis of Transport Phenomena (Professor Deen's book) and realized that I really like its field, despite the fact that I had never taken a transport course. When I looked up papers from the Deen group, I found the transport in membrane research of this group turned my interest into enthusiasm. I had also been looking for a project that would incorporate both numerical simulation and experimental work, and after a discussion with Professor Deen, I found a research home in his hindered transport work. Outside of the lab I enjoy reading international literature ( I like Chekhov) and figure drawing from life with charcoal and graphite.


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