Biman Bagchi
Ph. D (Brown), F.N.A, F.A.Sc., F.N.A.Sc.
Professor
e-mail : bbagchi@sscu.iisc.ernet.in
Intrenet : http://liquid.sscu.iisc.ernet.in
 
 
 
Research Work
     The main focus of our group has been theoretical studies of dynamical processes in liquids, polymers and glasses. We have used the methods of time dependent statistical mechanics and computer simulations to study various problems of interest in Physical Chemistry/Chemical Physics. In the following, we briefly discuss some of our areas of research.
A.   Chemical Reaction Dynamics
              We have worked on several different aspects of chemical reaction dynamics in liquids and dense gases. We have studied barrierless chemical reactions, activated processes such as isomerization reactions, carried out work on polar solvent effects on electron transfer reactions in solution and also investigated the effects of vibrational quantum modes in the Marcus inverted regime of electron transfer reactions.
          We have also worked on vibrational phase and energy relaxations in neat liquids and in binary mixtures.
B.   Solvation and Solvation Dynamics of Charged Species in Polar Liquids
    We have developed a microscopic theory of solvation and solvation dynamics in dense dipolar liquids which showed the breakdown of the famous "Onsager inverse snow-ball model" of polarization relaxation around a newly created ion due to the translational modes of the solvent. More recently, we have extended and refined his theory to explain the ultrafast Gaussian decay of the solvation time correlation function in liquid water and acetonitrile.
C.   Collective Orientational Relaxation
    We have developed a detailed first-principles statistical mechanical theory of collective orientational relaxation in dense dipolar liquids. The theory is based on a molecular hydrodynamic description where intermolecular correlations are included through a generalized free energy which is a functional of density. We have developed a theory to calculate the dissipative kernels which depend on and in turn also determines the collective orientational density and momentum variables (a kind of a boot-strap method).
D.   Electrochemistry: Transport Properties
    We have developed a microscopic theory of ionic diffusion and limiting ionic conductivity of electrolyte solutions – problems of great interest in electrochemistry. We have derived the classical expressions of Debye, Huckel, Onsager, Fuoss and Falkenhagen for concentration and frequency dependence of conductivity and viscosity of electrolyte solutions.
E.   Binary Mixtures: Anomalous Composition Dependence.
    We have shown that the well-known non-monotonic composition dependence of viscosity can be modelled by suitable construction of interactions among the two un-like species. We have also reproduced the experimentally observed anti-correlation between viscosity and excess volume.
F.   Conjugated Polymers: Electronic and Transport Properties
    Prof. Bagchi, along with Prof. Paul Barbara, Prof. Peter Rossky and others showed that the likely state of MEH-PPV in thin films is a collapsed, semi-ordered defect cylinder. The energy cost involving the formation (from an all trans conformation) of a cis defect and also a saturated defect has been calculated and found to be only a few Kcal/mol.
G.   Polymer Dynamics and Polymer Reactions
    We have worked on several aspects of polymer dynamics and reactions in polymers. We have demonstrated that the well-known Wilemski-Fixman theory of reaction between two ends of a polymer chain is satisfactory for certain values of the Forster rate parameters RF and krad, but is unsatisfactory when RF is large and/or when krad is close to the mean radius of the polymer chain. His group has also calculated the distribution of quantum efficiency for Forster energy transfer between two ends of a collapsing polymer chain subsequent to quench.
H.   Studies in Biophysical Chemistry
    Biophysical chemistry is now a major interest of the group. In the recent past we have developed a theory of dielectric relaxation of aqueous protein solutions. We have developed a molecular theory of chirality induced helical pattern formation in ammonia amphiphiles. More recently, we have studied the folding of head piece of villin (HP-36) by using a reduced hydropathy scale.
I.   Molecular Dynamics in Restricted Geometries
    Our group has studied orientational and solvation dynamics in restricted geometries, like cyclodextrin cavities, micellar and reverse micellar surfaces.
J.   Dynamics near Isotropic-Nematic Phase Transition
    We have carried out both theoretical and molecular dynamics simulation studies of single particle and collective orientational relaxation of the nematogens near the isotropic-nematic phase transition. The theory offers an explanation of the observed power law decay of the orientational order parameter.
K.   Dynamics of Supercooled Liquids
    Dynamics of supercooled liquid has been a subject of long standing interest of the group. Recently we have explored the probability of local density fluctuations, by using the density functional theory. We have also carried out MD simulations of correlated orientational and translational hopping of tagged isolated ellipsoids in binary mixtures.
L.   Applications of Mode Coupling Theory to Liquid State Dynamics
    Professor Bagchi and his group have applied the mode coupling theory of strongly correlated systems to study solvent dynamic effects on chemical relaxation processes, such as rotational and vibrational relaxation, isomerization dynamics, translational diffusion in supercooled liquids.
 
 
Representative publications
1.   R. Biswas and B. Bagchi, Solvation Dynamics in Slow, Viscous Liquids, J. Phys. Chem. (H.L. Friedman festschrift) 100 4261 (1996).
2.   N. Gayathri and B. Bagchi, Quantum and non-Markovian Effects in the Electron Transfer Dynamics in the Marcus Inverted Regime, J. Phys. Chem. 100 3056 (1996).
3.   S. Ravichandran and B. Bagchi, Orientational Relaxation in a Random Dipolar Lattice, Phys. Rev. Lett. 76 644 (1996).
4.   N. Nandi and B. Bagchi, Molecular Origin of the Chirality Driven Helical Pattern Promotion in Amphiphilic Monolayers and Bilayers, J. Am. Chem. Soc. 118 11208 (1996).
5.   R. Biswas and B. Bagchi, Activated Barrier Crossing Dynamics in Slow Viscous Liquids, J. Chem. Phys. 105 7543 (1996).
6.   N. Nandi and B. Bagchi, Ultrafast Solvation Dynamics of an Ion in Cyclodextrin Cavity: The Role of Restricted Environment, J. Phys. Chem. 100 1542 (1996).
7.   S. Bhattacharyya and B. Bagchi, Bimodality in the Dynamic Response of a Supercooled Liquid, J. Chem. Phys. 106 7262 (1997).
8.   N. Nandi and B. Bagchi, Dielectric Relaxation of Biological Water, J. Phys. Chem. B 101 10954 (1997).
9.   R. Biswas and B. Bagchi, Limiting Ionic Conductance of Rigid Symmetrical Ions in Aqueous Solutions: Temperature Dependence and Solvent Isotope Effect, J. Am. Chem. Soc., 119 5946 (1997).
10.   R. Biswas, S. Bhattacharyya and B. Bagchi, Vibrational Energy Relaxation, Non-Polar Solvation Dynamics and Instantaneous Normal Modes: Role of Binary Interaction in the Ultrafast Response of a Dense Liquid, J. Chem. Phys. 108 4963, (1998).
11.   B. Bagchi and R. Biswas, Ionic Mobility and Ultrafast Solvation: Control of a Slow Phenomenon by Fast Dynamics, Accounts of Chemical Research 31 181 (1998).
12.   B. Bagchi and N. Gayathri, Interplay between Ultrafast Polar Solvation and Vibrational Dynamics in Electron Transfer Reactions: Role of High Frequency Vibrational Modes, Advances in Chemical Physics, 107 1 (1999).
13.   N. Gayathri and B. Bagchi, Subquadratic Quantum Number Dependence and Other Anomalies of Vibrational Dephasing in Liquid Nitrogen: Molecular Dynamics Simulation Study from the Triple Point to the Critical Point and Beyond, Phys. Rev. Lett. 82 4851 (1999).
14.   B. Bagchi and R. Biswas, Solvation Dynamics, Ionic Mobility and Vibrational Relaxations: Understanding the Role of Biphasic Solvent Response, Advances in Chemical Physics 109 207 (1999).
15.   A. Chandra, R. Biswas and B. Bagchi, Molecular Origin of Debye-Huckel-Onsager Limiting Law of Ion Conductance and its Extension to High Concentrations: Mode-Coupling Theory Approach to Electrolyte Friction, J. Am. Chem. Soc. (Communication) 121 4082 (1999).
16.   K. Bhattacharyya and B. Bagchi, Slow Dynamics of Constrained Water in Complex Geometries, (Feature Article), J. Phys. Chem. A 104 10603(2000).
17.   A. Chandra and B. Bagchi, Frequency Dependence of Electrolyte of Electrolyte Conductivity , J. Chem. Phys. 112 1876 (2000).
18.   De Hong, Ji Hu, B. Bagchi, P. Rossky and P. Barbara, Single Molecule Spectroscopy of Conjugated Polymers, Nature 405 1030(2000).
19.   A. Chandra and B. Bagchi, Beyond the classical Laws of Electrochemistry: New Microscopic Approach, (Feature Article) J. Phys. Chem. B 104 9067(2000).
20.   N. Nandi, K. Bhattacharyya and B. Bagchi, Dielectric Relaxation and Solvation Dynamics of Water in Complex Chemical and Biological Systems, Chem. Rev. 100 2013(2000).
21.   B. Bagchiand S. Bhattacharyya, Mode Coupling Theory Approach to Liquid State Dynamics, Advances in Chemical Physics 116 67 (2001).
22.   G. Srinivas, Arun Yethiraj and B. Bagchi, Nonexponentiality of Time Dependent Survival Probability and the Fractional Viscosity Dependence of the Rate in Diffusion Controlled Reactions in a PolymerChain, J. Chem. Phys. 114 9170 (2001).
23.   G. Srinivas, A. Mukherjee and B. Bagchi, Non-ideality in the Composition Dependence of Viscosity in Binary Mixtures, J. Chem. Phys. 114 6220 (2001).
24.   K. Miyazaki, G. Srinivas and B. Bagchi, The Enskog Theory of Transport Coefficients of Simple Fluids with Continous Potentials, J. Chem. Phys. 114 6276 (2001).
25.   A. Mukherjee, G. Srinivas and B. Bagchi, Re-entrant Behavior of Relaxation Time with Viscosity at Varying Composition in Binary Mixtures, Phys. Rev. Lett. 86 5926 (2001).
26.   R. Vasanthi, S. Ravichandran and B. Bagchi, Needle-like Motion of Prolate Ellipsoids in the Sea of Spheres, J. Chem. Phys. 114 7989(2001).
27.   B. Bagchi, Relation between Orientational Correlation Time and the Self Diffusion Coefficient of Tagged Probes in Viscous Liquids: A Density Functional Theory Analysis, J. Chem. Phys. 115 (2001).
28.   S. Bhattacharyya and B. Bagchi, Anomalous Orientational Relaxation of Solute Probes in Binary Mixtures, J. Chem. Phys., (In Press).
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 

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