SACHIN SHANBHAG |
Shanbhag, S.; Lee, J.; Kotov, N.A., "Diffusion in Three Dimensionally Ordered Scaffolds with
Inverted Colloidal Crystal Geometry", Biomaterials, 2005, 26, 5581.
Using Brownian dynamics simulations, we probed the resistance offered by highly ordered ICC scaffolds to nutrient transport. For typical dimensions of the scaffold, we found that the effective diffusivity was reduced to about 30% of the free solution diffusivity (D_eff=0.3 D_0). Modeling cells (very crudely) as finite-sized colloidal particles, we found that the effective diffusivity of a cell in an ICC scaffold decreased linearly with cell size. Online article |
Shanbhag, S.; Larson, R.G., "The Chain Retraction Potential in a Fixed Entanglement Network",
Phys. Rev. Lett., 2005, 94, 076001.
In this paper, we adapted the primitive path identification algorithm to suit a lattice description, and combined it with the bond-fluctuation model to compute the primitive path length distribution. This distribution can be recast into a retraction potential, which specifies the entropic barrier encountered by the tip of a chain, tethered at one end, and forms the underlying basis of the tube model for branched polymers. We found that the potential is quadratic and has a prefactor close to 1.5 as derived by Doi and Kuzuu, and in contradiction with early lattice models. Online article |
Park, S.J.; Shanbhag, S.; Larson, R.G., "A hierarchical algorithm for predicting the linear
viscoelasticity of polymer melts with long-chain branching", Rheol. Acta, 2005, 44, 319.
This paper is a generalization of the "hierarchical model" in which early time fluctuations are included. It presents comparisons with experimental data on 1,4-polybutadienes and 1,4-polyisoprenes for a variety of linear, branched and polydisperse structures. Online article |
Shanbhag, S.; Larson, R.G., "A slip link model of branch-point motion in entangled polymers",
Macromolecules, 2004, 37, 8160.
When a short arm is grown on a linear backbone (asymmetric stars) the existing "tube" theory fails to predict how rapidly the motion of the branch-point becomes quenched. We include an extreme form of branch-point motion in a slip link model and find that it can explain the anomalously rapid quenching of the branch-point if we assume that the time scale of the branch-point motion is set by the time required for the short arm to escape all entanglements, including those newly created while others are destroyed. The algorithm successfully predicts the linear viscoelasticity of H-polymers, where the acceleration induced by the polydispersity offsets the sluggishness introduced by adopting a drastically slow time scale for diffusion of the branch-point. Although the theory becomes unrealistic for long arms, it raises important questions about existing theories of branch-point motion and provides some clues to their resolution. Online article |
Sen, T.K., Shanbhag, S.; Khilar, K.C., "Subsurface colloids in groundwater contamination:
A Mathematical model", Colloids Surf. A., 2004, 232(1), 29.
In this paper, an equilibrium three-phase model based on colloidal induced release, migration and finally capture of these colloidal fines at pore constrictions was developed. It was found that the presence of colloids can either facilitate or inhibit the spreading of contaminants. For a range of conditions, plugging of the porous media occurs resulting in retardation of contaminant transport which can be used to develop new containment techniques. Online article |
Shanbhag, S.; Larson, R.G.; Takimoto, J.-I.; Doi, M., "Deviations from dynamic dilution in
the terminal relaxation of star polymers", Phys. Rev. Lett., 2001, 85, 195502.
In this paper, we proposed a simple virtual space "slip-link" model for relaxation of entangled star polymers that accounts for chain-end fluctuations and constraint release and that explains deviations from the "dynamic dilution" equation observed in recent dielectric and stress relaxation data. In the terminal regime where tube expansion fails to keep up with chain relaxation, relaxation is controlled by rare events in which newly created entanglements near the branch point draw the chain end towards the last remaining old entanglement, where a shallow fluctuation releases it. Online article |
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© 2008 Sachin Shanbhag
Last Modified: 10/01/2008
Last Modified: 10/01/2008