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

Telephone (617) 253-6490
Email: bhalla@mit.edu

Gaurav Bhalla

Graduate Research Assistant

Research Interests

Hydrodynamic theory for osmotic reflection coefficients

My research investigates the osmotic flow of macromolecules in porous membranes. The research is based on the modifications to the point-wise momentum conservation equations necessitated by the presence of finite sized molecules. In particular, my work will extend the model of the Anderson and Malone (1974), wherein a mechanistic model for osmotic flow of macromolecules in porous media is developed from classical transport and thermodynamic considerations.
The significance of the pore is in the confinement of the fluid phase. The presence of the pore wall then acts as a steric hindrance to the solute molecule due to its finite size. The centroid of such a macromolecule cannot be closer than a radius from the solute wall due to these steric limitations. This limit can be thought of as a solute exclusion effect or the development of a solute-wall potential field. The assumption of osmotic equilibrium of the solvent then leads to the development of a radial pressure gradient that must balance the potential force acting on the solute. This pressure gradient in turn has an axial component due to the dependence on the concentration which in turn drives the flow. My approach is novel and has interesting applications in more complicated geometries such as fibrous membrane and gels. Such extensions are the main objective of my work.
A fundamental question that needs to be addressed early on is the issue of the solute-solvent force interaction. The previous work assumes that this interaction occurs at a point, an obvious choice for this point being the center of mass of the solute molecule. However, strictly speaking this force interaction occurs on a surface instead and therefore a "smeared" solute-solvent force transmission would be a better approximation to the true picture. Specifically my plan will address the following:
1 A better description of the solute-solvent force transmission;
2 Prediction of the osmotic reflection coefficient for capillary pores with hard-particle-hard-wall interactions and the effect of the solute size and shape;
3 The osmotic reflection coefficient for capillary pores with charge effects;
4 Prediction of the osmotic reflection coefficient for fibrous membranes and gels with parallel fibers with and without charge effects;
5 Experimental test of the model predictions.

Personal Interests

On my own I like to follow international cricket matches, especially the India versus Pakistan matches. And I follow the stock markets, doing a little bit of day trading on my own, with my almost hypothetical amount of money.