Research
Quantum Dynamics And Thermodynamics At Finite Temperatures:
"Newtonian mechanics cannot be improved, it can only by replaced by something essentially different!" [Werner Karl Heisenberg]
Quantum particles, such as electrons and light atoms including hydrogen, are ubiquitous in many chemical and physical systems of current interest. Often understanding the dynamics and thermodynamics of these particles is of crucial importance. Arguably nowhere is this more significant at present than in the search for sources of clean energy. Here proton diffusion through membranes, hydrogen storage materials and electron transport for solar devices are just but a few examples of the role of mobile quantum particles. Since its original formulation in 1948, Feynman's path integral representation of time-dependent quantum mechanics has provided a powerful tool for studying many-body problems at finite temperatures without introducing uncontrolled approximations. We are developing and applying novel path integral techniques to understand the quantum world at the nanoscale and finite temperatures. Fundamental research is directed towards the atomistic level understanding of phase transitions and quantum dynamics at nanoscale confinement.
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Adsorption-Induced Deformation Of Porous Media:
"Experiment without theory is blind; theory without experiment is lame." [Immanuel Kant]
Global warming, caused by a build-up of greenhouse gases, in particular carbon dioxide, in the atmosphere, has led to numerous proposals on how to capture and store carbon dioxide in order to mitigate the damaging emissions from fossil fuels. It is not economically feasible to store the carbon dioxide in nanoporous materials because of their high concentration in the atmosphere. The sequestration of carbon dioxide into geologic formations is very promising method. Moreover, because the binding energy of carbon dioxide with the carbon matrix is higher than methane, the coalbed methane is displaced and desorbed during the carbon dioxide geosequestration. Thus, the invested money can be partially recovered. In practice, injected and compressed carbon dioxide produce a very high internal adsorption stress that can result in swelling of the coal matrix. Detailed understanding and prediction of adsorption-induced deformation of coal matrix upon geosequestration is crucial for avoiding of ecological catastrophes, such as leakage of carbon dioxide from underground reservoirs to water. Moreover, as has been experimentally reported the efficiency of carbon dioxide geosequestration can be drastically reduced due to closing of pores as well as transport channels by the swelled coal matrix. We are developing and applying new theory of adsorption-indiced deformation of porous material in order to understand this complex phenomenon.
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Structural And Energetic Heterogeneity Of Porous Materials:
"All science is either physics or stamp collecting." [Ernest Rutherford]
Nanoporous materials (solid materials having pores of nanometer dimension) have numerous applications in separations, medicine, energy storage, catalysis, environmental protection, biotechnology, electronics, photonics, etc. The reduced dimensionality of nano-scale systems is a key to control the reaction rate, separation efficiency, photonic band gap, delivery of drugs, etc. However, the internal structure of many porous materials (such as: activated carbons and carbon fibers, microporous and mesoporous molecular sieves, carbosils, and others) is still poorly understood. Currently available methods for pore structure characterization are primarily based on macroscopic thermodynamics, and, thus, are not applicable at the nanoscale level. We are developing and applying modern methods of statistical and quantum mechanics to study interactions of fluids with heterogeneous surfaces and nanopores. Fundamental understanding of gas adsorption and separation of fluid mixtures in nanopores is essential for pore structure analysis of ill-defined materials of industrial importance.
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Coarse-Grained Force Fields For Molecular Mechanics Calculations:
"Physics is like sex. Sure, it may give some practical results, but that's not why we do it." [Richard Feynman]
Computer simulations that take into account all the microscopic forces, i.e., fully atomistic simulations, will in principle provide accurate descriptions of complex systems, such as soft materials or bimolecular systems. However, they are strongly limited by the computational resources available that usually do not allow mesoscopically and macroscopically relevant size and time scales to be reached. Coarse-graining (CG) of these complex systems is a fundamental problem of modern statistical mechanics for which a general solution has not been found yet. We are developing and applying novel CG techniques to understand the inherent loss of atomistic information at the CG level.
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Equilibrium Clusters in Concentrated Protein Solutions:
"The information encoded in your DNA determines your unique biological characteristics, such as sex, eye color, age and Social Security number." [Dave Barry]
Spatial distribution of proteins in physiological solutions is very important for living matter; individual particles or clusters of particles can be associated with quite different properties or functions. In particular, a change of structural properties may lead to different diseases. For this reason it is important to understand how different factors influence the structure of proteins in different solutions.We are developing and applying a physics approach to understand the properties of salt-free protein solutions near physiological conditions.
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Adsorption and Separation of Fluid Mixtures in Nanoporous Membranes:
"Only the individual can think, and thereby create new values for society ..." [Albert Einstein]
The study of adsorption and separation of complex fluid mixtures on novel nanoporous materials is appealing from both practical as well as fundamental perspectives. From a practical perspective: developing methods to efficiently capture greenhouse and ozone-depleting gases is a challenge with enormous environmental implications. From a fundamental perspective: nano-spaces have a distinctively strong interaction potential for molecules, giving rise to unusual confinement effects. The nanoconfinement effect can accelerate a separation of fluid mixture components without the use of expensive technologies (e.g. absorption of carbon dioxide onto various amine-based solvents, cryogenic distillation, etc.). We have been studying various subjects related to the fundmanetal understanding of fluids at the nano-scale confinement. In particular, we have been focus on the problem of carbon dioxide capture and storage.
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Reconstruction of Amorphous Ill-Defined Materials:
"The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them." [William Lawrence Bragg]
An amorphous solid is a liquid that does not flow. Like liquid, amorphous material has some short-range order at the atomic length scale due to the nature of chemical bonding. Like solid, amorphous material is rigid and holds its shape. The physicochemical properties of amorphous materials are strongly dependent on the spatial distribution of atoms. Therefore, the microscopic insight into the degree of local order: in particular, the coordination to nearest neighbors, hybridization, and percolation threshold, is crucial to understand how the molecular configuration within a single amorphous phase affects these properties. Theoretical description of ill-defined nonporous materials are far more complicated because these materials consist of two phases: amorphous phase and various pores. The goal of reconstruction algorithms is to built microscopic model that mach experimental structure data (i.e. structure factor, high-resolution TEM images, etc.) of real material, at least in a qualitative way. Unfortunately, this is an ill-posed problem because the number of atomic configurations that mach the experimental structural data are infinite. Can we really reconstruct the three-dimensional atomic structure of ill-defined nanoporous material from incomplete experimental knowledge ?. We are developing and applying novel algorithms (such as Hybrid Reverse Monte Carlo Simulation) in order to solve this fundamental problem.
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