A hierarchical modelling technique is used for analysis of steady state and dynamic characteristics of fuel processing units used in portable power generation applications. The reaction kinetics were obtained by a posteriori reduction of microkinetic models. Two-dimensional Computational Fluid Dynamics (2D CFD) models, 1-D heterogeneous reaction models, idealised reactor models and simplified models based on unit-level mass and energy balances are developed and used to map various operating regions for small-scale devices. In addition to the steady-state device design, the objective of this approach is to illucidate the effect of various design parameters on optimal design, to investigate of fast ignition behaviour and to develop low complexity control-oriented models. Specifically, this talk will focus on the following applications: (i) Fast auto-ignition in catalytic microburners (ii) Model simplification and catalyst patterning for thermally coupled microreactors (iii) Integrated Fuel Processing / Fuel Cell control

One of the major implications of Darwin~Rs evolutionary theory is the fact that all species on this planet are related to each other and that they evolved from one common ancestor. Darwin's articulates this idea in his dream scenario ~V ~Sto have fairly true genealogical trees of each great kingdom of Nature". Today we are close to realizing Darwin~Rs dream through molecular phylogenies. In this talk I will present one of the applications on molecular phylogenetics, particularly in the field of biogeography. Biogeography is the study of distribution of species (biodiversity) in space and time. Here I will discuss how phylogenies have been used to understand the current distribution of species in India.

Supercritical fluids (SCFs) are fluids above its critical temperature and critical pressure. They have several attractive properties such as gas-like diffusivity, liquid-like densities, high compressibility and negligible surface tension. These unique properties make them attractive solvents for many industrial separation processes. Supercritical carbon dioxide (SCCO2) is commonly used because of its abundant availability, near-ambient critical temperature and its non-toxicity. However, polar substances are poorly soluble in SCCO2 but these solubilities can be enhanced by adding 1 to 5 mol % of polar entrainers. The design of any supercritical process needs accurate experimental data on solubilities of solids in the supercritical fluids (SCF).

In this study, both the experimental determination and thermodynamic models of solubilities have been investigated. In determination of solubilities of solids, we have considered three types of non-volatile solids namely long chain naturally available free fatty acids, chlorophenol derivatives and an anti-inflammatory drug. New thermodynamic models and existing models were used to model the experimental data obtained in this study and also data reported in the literature.

Four free fatty acids considered for the study were lauric acid, myristic acid, palmitic acid and stearic acid. The solubilities of these fatty acids were determined with and without cosolvents. For each compound the effect of temperature, pressure and cosolvent concentration has been investigated. The solubilities of lauric acid and myristic acid were correlated with an equation of state (EOS) with single adjustable parameter. The solubilities of palmitic acid and stearic acid were modeled by Mendenz-Santiago and Teja models.

Palmitic acid and stearic acid solubilities in pure SCCO2 were estimated at high temperature and the solubilities were correlated with several models. Temperature independent models considered for the studies were Peng Robinson Equation of state with Kwak Mansoori mixing rules, Mendenz-Santiago and Teja models and reformulated Chrastil model. An enhancement in solubilities of fatty acids in supercritical fluids was observed in presence of cosolvent as well as with increase in pressure.

The solubilities of some chlorophenols have been estimated in SCCO2 with and without cosolvents (methanol and acetone). The solubilities were correlated with Chrastil models and Mendenz-Santiago and Teja models. An enhancement in solubilities of solids in supercritical fluids was observed in presence of cosolvent as well as with pressure. The overall order for the solubilities of chlorophenols is 2, 4-dichlorophenol > 4-chlorophenol > phenol > 2, 4, 6-trichlorophenol > pentachlorophenol, which is the same order as the sublimation pressure of these compounds.

The equilibrium solubility of an anti-inflammatory drug namely, n-(4-ethoxyphenyl)ethanamide in SCCO2 was measured. Both EOS and semi-empirical models were successfully used to correlate the experimental data.

Peng Robinson Equation of sate (PREOS) in combination with Valderrama modification of Kwak and Mansoori mixing rules (mKM) has been used to correlate anti biotics and anti-inflammatory drugs in SCCO2. In this work, the sublimation pressure was used as an adjustable parameter together with the binary interaction parameters. The optimization procedure directly gives the binary interaction parameters along with sublimation pressure expression coefficients From these coefficients, the vapor pressure and enthalpy of sublimation, ( ) was estimated. The estimated Sublimation enthalpies were compared with the values estimated from Bartle et al. model and experimental values. The proposed model found to be successful in estimating sublimation enthalpies from solubilities.

New dimensionally consistent solvate complex models are developed. These models are compared with standard solvate complex models of Chrastil, González et al., Adachi and Lu model and del Valle and Aguilera by correlating several binary and ternary systems. New models were successful in correlating the solubilities both in presence and absence of cosolvents and these models are dimensionally consistent in contrast to the models reported in the literature.

Matter is electrically neutral on macroscopic scales, but interfaces of materials are almost always charged. We are reminded  of this in small ways in our daily lives; for example a plastic ruler becomes charged and attracts bits of paper when  rubbed on clothing.  These interfacial forces being proportional to the surface area are however often dwarfed by volume forces such as gravity. The situation changes dramatically on very small scales (roughly a 100 micron or  less). At an interface of a dielectric and an ionic liquid, these charges cause a significant  flow when an external electric field is switched on.  Such micro-scale flows have important applications in recently developed and rapidly evolving  technologies such as microfluidics and  nanotechnology. In this talk I will first introduce the mathematical tools for describing such small scale electrically driven flows and their  transport properties. Then I  will illustrate with some recent applications. 

Spherical colloids have been used successfully as condensed matter model systems to study fundamental aspects of crystallization, phase behaviour and dynamic processes (glass transition). Relatively new and challenging is the synthesis of enough anisotropic particles such that one can study their phase behaviour in real space. In the first part of my talk, I present a new method for making a new colloidal model system of 'chains of beads' using a combination of dipolar interactions induced by an external electric field, and the interactions between the charged micron-sized particles. We will show that it is possible to make linear chains of beads starting from a dispersion of monodisperse colloidal spheres with yield of above 90%. We will show preliminary results on making chain of beads monodisperse in length and, furthermore, how it is possible to manipulate the flexibility of the chains [1]. In the second part of my talk, I will focus on "directing colloidal self-assembly with biaxial electric fields". Nowadays, one can often predict what structure is needed to obtain certain material properties; the challenge is to experimentally realize the particle interactions that lead to these structures. External fields provide one route. Uniaxial electric and magnetic fields are commonly used to induce dipolar interactions, while multi-axial fields bear promise for higher complexity of the interactions. Here, we focus on a high-frequency biaxial electric field, which can induce 'inverse' dipolar-interactions, and study in detail how it affects the colloidal self-assembly process. We find that spherical particles reproducibly form what we think are non-equilibrium structures of hexagonal 'sheets', which we can make permanent by thermal annealing. Moreover, we can rapidly switch the suspension structure from isotropic, to one-dimensional strings and two-dimensional 'sheets'. This is interesting for applications, because the suspension properties can be strongly anisotropic [2]. Reference: [1]. H. R. Vutukuri, A. Imhof, A. van Blaaderen, to be published [2]. M. E. Leunissen, H. R. Vutukuri, A. van Blaaderen, Advanced Materials 21, 1-5, (2009).

On-line monitoring of particle shape and size distribution is a challenge frequently faced by the traditional pharmaceuticals and fine chemicals industries. The control of particulate processes is particularly compounded by the lack of process understanding and in-situ sensors. With regulatory initiatives such as the US Food and Drug Administration's (FDA) Process Analytical Technology (PAT) program for the pharmaceutical industry and the ongoing improvement in real-time imaging hardware (exemplified by Focused Beam Reflectance Measurement, FBRM and Particle Vision and Measurement, PVM, both from Lasentec), there is a growing interest to develop control technologies using advanced imaging sensors. In this work, I will describe some of our research in image analysis targeted at real-time control of crystallization processes.

Based on the sequence differences, HIV-1 is classified into several families technically called subtypes or clades. Of these various clades, subtype-C strains of HIV-1 are predominant in the world causing almost 56% of the global infections. In India, subtype-C is responsible for nearly 99% of the viral infections. My laboratory at JNCASR focuses on the biological properties of the Indian HIV-1 to understand the factors that underlie the successful expansion of subtype-C strains globally. In my talk, I will present experimental data to demonstrate that subtype-C of HIV-1 dominates the Indian epidemics. Furthermore, I will introduce two independent observations and one hypothesis that these observations, with respect to HIV-1 neuro-pathogenesis, are functionally associated. We propose that a single amino acid variation in the subtype-C Tat protein compromises its chemokine signaling property and as a consequence, recruitment of monocytes to the brain in AIDS. We will argue further that the attenuated chemokine property of subtype-C Tat is directly correlated to the reported low incidence of HIV-associated dementia (HAD), a manifestation of neuron death following viral infection of the brain, in India as compared to that of subtype B HIV infections of the West. I will present data in support of our hypothesis that subtype-C Tat protein is a defective monocyte chemokine. Additionally, I will discuss the implications of this finding and how this hypothesis influenced our understanding of HIV neuro-pathogenesis.

Particulate multiphase flow involves the mechanics, flow, and transport properties of mixtures of fluid and solids.  Their behavior differs significantly from those of molecular fluids, and as a result the classical models, (e.g. the Navier-Stokes equations), are incapable of describing their response to applied forces.  Multiphase systems are intrinsic to the rheology of emulsions and suspensions, flocculation and aggregation, sedimentation and fluidization, flow of granular media, nucleation and growth of small particles, attrition, and solidification processes. Many new and intriguing flow phenomena occur as a result of poorly understood physical mechanisms present here and absent in single phase flows. This talk will be concerned with the flows of solid particles in a pipe going from viscous to turbulent regimes. The first part of the talk will focus on neutrally buoyant particles. It will review some results on (i) the collective migration of particles at low Reynolds number and (ii) the lateral inertial migration of single particles as a function of the Reynolds number, and (iii) will show that particles can modify the transition to turbulence that occurs in a single-phase flow and can indeed trigger the transition. The second part of the talk will examine a bed constituted of sediment particles submitted to a pipe flow. It will discuss (i) the critical condition for incipient motion of the grains, (ii) bed-load transport, and (iii) will show that the evolution of the particle bed exhibits different dune patterns as the flow is increased from the laminar to the turbulent regimes.

Vertebrate arteries undergo several million cycles of pulsatile motion, without appreciable fatigue, over the typical lifetime of an organism. In contrast to traditional engineering materials, they also constantly adapt their geometry, material composition and mechanical properties in response to the changing mechanical and biochemical environment. The structural integrity of blood vessels depends critically on the underlying passive structural proteins along with active muscle cells. In recent years, the study of Tissue Biomechanics has evolved into a fascinating area in which engineers and physicists can contribute towards the understanding of biological tissues and their function. My research focuses on three questions: First, what can we learn from quantifying the mechanical design principles in arteries? Second, how can we reconstruct their complex and composite mechanical properties based on their individual components? Finally, how can we model their biomechanical response? I will address these questions using a combination of experimental techniques and constitutive modeling.

To identify a black hole in the universe one needs to understand behavior of infalling matter around it. In absence of significant molecular viscosity the underlying transport mechanism, which forms an accretion disk, is still an open question when this is presumably a turbulent transport. However, similar problem also arises in explaining turbulence in plane channel flows in a laboratory. In this talk, first I will explain a possible solution of this problem which helps us to understand transport of matter towards a black hole. Next, I will extract the fundamental properties of black holes, e.g. spin, from the behavior of infalling matter which will give a test of Einstein general theory of relativity.

DNA has attractive physicochemical characteristics such as robust thermal and hydrolytic stability. It also has desirable structural characteristics stemming from predictable and specific recognition properties that give rise to a highly regular helical structure which behaves as a rigid rod on length scales upto ~50 nm. Since these rigid rods may be welded together by complementary base-pairing, DNA is now taking on a new aspect where it is finding use as a construction element for architecture on the nanoscale. This field is called structural DNA nanotechnology. I describe approaches adopted by my lab where we demonstrate promising new assembly strategies that include the use of unusual forms of DNA in structural DNA nanotechnology to make chemically responsive DNA scaffolds. I will then go on to show the application of these chemically responsive DNA scaffolds in biological systems.

Many naturally occurring as well as* *man made materials comprise of large number of crystallites with a preferred orientation. The preferred orientation, popularly known as texture, governs various structural and mechanical properties of these materials. Texture may get developed/modified during different states of materials processing like solidification, plastic deformation, annealing and phase transformation. It is possible to tailor texture in materials to enhance a particular property. Traditionally, X-ray and neutron diffraction had been used to study texture in materials. It has been very recently that other techniques based on synchrotron X-rays and SEM based Electron Backscattered Diffraction have been developed for complete characterization of texture in materials. In this presentation, the author will introduce the state of the art in the field and the work that is being carried out in the institute in this area.

Ribavirin, a nucleoside analog, is used in combination with interferon alpha to treat hepatitis C virus (HCV) infection. 30-70% of the patients treated respond to combination therapy, whereas interferon monotherapy elicits a response in only 20% of the patients. Thus ribavirin appears crucial for HCV treatment. However, ribavirin treatment causes a side effect, anemia, where hemoglobin levels in patients are reduced. Due to this adverse effect, patients are forced to reduce the ribavirin dosage or even stop treatment, thereby lowering treatment response. It is therefore important to determine the optimal dosing protocols for ribavirin that maximize the response rates while keeping anemia under control. Models of antiviral response to ribavirin have been developed. No models exist that describe how anemia develops during ribavirin therapy. We have developed a population balance model to predict the reduction of hemoglobin during ribavirin therapy. Model predictions capture experimental observations, yield estimates of erythrocytes~R lifespan in HCV patients, and present a framework for optimization of ribavirin therapy.

A granular material is a collection of discrete, solid particles of macroscopic size dispersed in an interstitial fluid, in which the fluid has an insignificant effect on the particle dynamics. Because they exhibit fascinating properties because of dissipative interactions, due to their importance in geophysical and industrial processes, flows of granular materials have been the focus of large amount of research involving physicists and engineers. A good understanding of the physics of granular materials is desired in order to design efficient processing and handling systems. Granular materials can be heaped like a solid, and can flow like a fluid. Though the two distinct regimes of granular flows are well described by kinetic theory (rapid flows) and plasticity theories (quasi-static), the intermediate dense flow regime, where collisional and frictional interactions are important, is not yet described succesfully. In this thesis, we examine the applicability of kinetic theory for dense granular flows, the structure and dynamics in sheared inelastic hard disks systems and dynamics of sheared non-spherical particles.

At the meso and nano scale, interactions like the van der Waal , steric, acid-base, electrostatic, etc. or externally imposed fields like electric field, thermal gradient or mechanical stresses, etc. often lead to instabilities, self organization and pattern formation in soft, confined thin films. The concept of self organized pattern formation, which is distinct from better known top down patterning methods (various types of Lithography) or the bottom up "Self Assembly" techniques, can be used to create structure formation with sub-micron and meso scale dimensions over large areas (~cm2). However, the utility of the resulting structures, which have a well-defined mean length-scale, is often limited by lack of long range order. Here, we present some strategies by which the pattern dimension, length scale and morphology can be controlled by template induced lateral confinement or by tuning properties like the film thickness, surface and interfacial tension etc. In course of this lecture, we will discuss how novel concepts like beyond the master patterning, patterns on demand by in-situ modification of the structures, fabrication of embedded structures can be achieved by self organization. We show how critical the relative magnitudes vis-a-vis the commensuration of individual lengthscales: that of the natural instability and of the confining template are, on the morphology of the final patterns. In addition, I will also briefly discuss my recent work on spin coating induced colloidal particle array formation using flexible patterned templates.

The advent of PAT principles proposed by the USFDA for the life sciences industry has opened up many possibilities for the application of systems engineering tools such as data analysis, reduction, monitoring and control to the area of batch process manufacturing. Such tools are generally oriented towards achieving improved and consistent yields to minimize batch-to-batch variation, as well as provide early advisories related to potential failure / contamination or unacceptability of an evolving batch. Batch fermentation processes are excellent examples of very high value, low volume and demand specific specialty products that follow a proprietary, a priori established manufacturing recipe. The manufacturing costs are significantly high. The process is fraught with risks of contamination by foreign microorganisms and lower product yields due to suboptimal operation or deviations from prescribed behavior due to disturbances. Batch-to-batch variations due to uncertain initial conditions such as quality of inoculums are also commonly seen. There is therefore a strong incentive to develop and deploy strategies for advanced monitoring, fault diagnosis and performance control for such processes. This seminar will focus on some recent approaches for real time performance monitoring, control and quality assurance for pharmaceutical processes. Illustrative examples from representative batch systems will be used to highlight critical issues in the monitoring and control tasks. Validation results involving simulations and experimental data will be presented.

The large-scale implementation of a natural gas based consumer transportation infrastructure has been limited by the absence of the safe and economical techniques of on-board storage of natural gas. Presently, natural gas is stored as compressed natural gas in heavy steel cylinders under pressures of 200-250 atm. However, such a method of storage has certain disadvantages which include costly multi-stage compression costs and limited driving range. Hence, other alternative method of storage like adsorbed natural gas which involves adsorbing natural gas at moderate pressures and room temperatures are currently being explored. Among the currently available storage media, activated carbons and related carbon-based nanoporous structures have garnered tremendous interest due to their unusually high adsorptive capacities. However, systematic improvement of these materials relies on a fundamental understanding of the physical and chemical processes that govern the basic interactions between the gas molecules and their substrate. In an attempt to address these shortcomings, we present here extensive energetic calculations of methane adsorption in model carbonaceous systems using density-functional techniques and grand canonical Monte Carlo simulations. As exact microstructures of activated carbons are notoriously difficult to characterize, we have instead attempted to isolate nanostructures and defects most likely to be found in these materials. These include surfaces, edges, and point defects, as well as chemical functionalization. For each of these nanostructures, we analyze changes in the structural, magnetic, and electronic properties upon adsorption. The defect structures exhibiting strongest methane adsorption are isolated, and the relevant mechanisms dominant in binding are identified.

Vibrofluidised granular beds are often used as an idealisation of granular flows as they provide a convenient approximation to the simplest type of flow: steady state, binary and instantaneous collisions with no rotation. In this research work, we explore the behaviour of vibrofluidised 3D granular beds by developing various models based on the granular kinetic theory approach. In the first case, an inviscid model for a vibrofluidised granular bed was developed using only observable system parameters such as particle number, size, mass and coefficients of restitution. Two closures based on granular kinetic theory were described, one the standard Fourier law relating heat flux to temperature gradient, the other including an additional concentration gradient term. Both closures result in solutions that are in reasonable agreement with the experimental results from the technique of Positron Emission Particle Tracking (PEPT) without any fitting parameters. It was found that differences between the predictions of each of the closures were relatively small in comparison to the anisotropy of the experimentally determined temperature distribution. Subsequently, considering the viscous effects on the system, a full Navier-Stokes like viscous model was developed using the Standard Fourier type heat flux based on granular kinetic theory. The resulting granular temperature and packing fraction profiles compare well against the inviscid model and the PEPT experimental results suggesting that the viscous effects are small. The mean velocity profiles from the viscous model show the presence of asymmetric toroidal convection rolls in the system that match well with the shape of the roll observed in the experiments. Quantitatively, the mean velocity profiles show good agreement with the experimental results at relatively low altitudes for a range of experimental values. Additionally, the wall effects were explored in the model which shows that the convection rolls are influenced by the sidewall restitution coefficient, a result that was earlier confirmed using the molecular dynamics (MD) simulations. The viscous model was extended to predict the behaviour of an annular vibrated 3D granular bed. The results from the model were compared with the molecular dynamics (MD) simulations and experimental data obtained using PEPT. A comprehensive analysis to probe other key factors that control the direction and magnitude of convection rolls was carried out. This involved a study on five critical variables namely, the inner and outer wall coefficients of restitution, number of grains, ratio of surface areas of the inner and outer cylinders and base amplitude. The results from a systematic study indicate that all the five variables examined can influence the direction and magnitude of the convection rolls in the system. However, it is determined that to initiate convection rolls the presence of energy dissipation at the walls is required. Finally, a comparison between the double convection rolls previously observed experimentally and in simulation shows excellent agreement suggesting that the model may further be used to study the transition from single convection to double convection roll motion of the grains and to explore the precise experimental conditions under which double rolls occur.

This talk would start with a brief background in optical characterization and its application to study of micro/nano particles. It is an area of study that is significant for biomedicine, semiconductor metrology, and nanotechnology. Specific applications in high speed single cell cytometry, identification of pathogenic colonies, detection/characterization of nano dust on substrates, micro-devices and nanophotonics would be discussed. To conclude, the significance of chemical engineering discipline in few of the above applications would be highlighted.

First-principles models at electronic and atomic scales offer exciting opportunities for rationally designing novel chemical engineering technologies with a broad range of applications. However, the practicality of using first-principles methods for design is limited by two challenges that are found to recur in several different systems. The first challenge lies in overcoming the large separation of length and time scales, typically ranging from nanometers to centimeters, and picoseconds to minutes. The second challenge is the combinatorial complexity associated with generating structure-property-fabrication phase diagrams for rational design. These challenges render first-principles methods computationally intractable.
In this talk, I will present a bottom-up multiscale modelling framework, which we have developed recently, to overcome these underlying challenges by deriving a hierarchy of atomistic, mesoscopic and continuum models directly from first-principle methods while retaining the accuracy. Bottom-up multiscale models are extremely useful for chemical engineering design as they can i) provide fundamental insights into key mechanisms at different scales that cannot be modelled with classical continuum equations, ii) help discover new materials for improving the performance and/or reducing cost, and iii) enable the prediction of device performance under different operating conditions and/or at long time scales. The strength of these methods will be highlighted through a specific example of design of high-density nanoparticle arrays for catalytic or electronic applications. Current approaches for fabricating high-density nanoparticle arrays rely on trial-and-error. I will present a systematic, rational design strategy that employs bottom-up multiscale models in conjunction with optimal control theory to identify the fabrication conditions that lead to the desired nanoparticle array. Atomistic, coarse-grained and continuum bottom-up multiscale models will be employed to model the self-assembly of the nanoparticles, and to generate a structure-fabrication phase diagram for the nanoparticles array.

A fluid heated to above the critical temperature and compressed to above the critical pressure is known as a supercritical fluid. The densities of supercritical fluids are comparable to that of liquids, while the viscosities and diffusion coefficients are comparable to that of gases. This enhances the rates for diffusion controlled reactions. The low water activity environment shifts the thermodynamic equilibrium of hydrolytic reactions to favor synthesis. Also, reactions in which water is a product can be driven to completion. Since enzymes are insoluble in supercritical fluids, recovery is straightforward. The product fractionation and purification from the reaction mixture are accomplished by reducing the pressure in a sequence of separators. Further, traces of the supercritical fluid on the system will not lead to adverse effects and thus the synthesis of food products and pharmaceuticals in supercritical fluids is considered green. Thus enzymatic reactions in supercritical carbon dioxide combine the advantage of biocatalysis (substrate specifity under mild reaction conditions) and supercritical fluids (high mass-transfer rate, easy separation of reaction products from the solvents and environmentally benign). In this study, three types of enzymatic reactions namely hydrolysis, esterification and transesterification have been investigated. A wide variety of flavors, pharmaceuticals and biodiesel has been synthesized by using these techniques. In each case, the effect of various parameters such as enzyme, temperature, enzyme loading, and water content have been investigated. The rates of the reactions have been modeled based on the Ping-Pong mechanism to determine the kinetic parameters.

Agitated liquid-liquid dispersions are used to provide high contact area between two immiscible liquid phases. This is accomplished by dispersing one phase into the other in the form of drops. Throughput of operation can be increased by increasing the dispersed phase volume fraction. However, at a critical volume fraction, an instability sets in. The dispersed phase becomes continuous and vice versa, nearly catastrophically. This phenomenon, known as phase inversion, has been studied over the last five decades. A mechanistic understanding of the phenomenon is however yet not available. Population balance based approaches in which first order drop breakup and second order coalescence are considered to occur independently fail to predict onset of an instability for realistic kernels.
A new drops formed through breakup and coalescence processes can come in collisional contact with neighbouring drops and coalesce with them to form new drops, which can repeat the same process, and so on, giving rise to a coalescence cascade. The role of coalescence cascades in liquid-liquid dispersions is recognized in this work, and is investigated for its effect on stability of dispersions for the first time using two approaches---kinetic Monte-Carlo (MC) simulations and mean-field models. The MC simulations capture an instability---the average drop size at steady state approaches infinty at a critical value of volume fraction, which mimics the instability leading to inversion of phases. Similar simulations to capture dispersal of sticky particles show a similar phenomenon. Sticky particles can be finely dispersed only if their volume fraction remains below a critical value. At the critical value and above, stickly particles cannot be completely dispersed. The critical volume fraction $\phi_c$ scales with dimensionality $D$ of space as $2^{-D}$. A mean field model with cascades of order up to infinity is developed. The model captures the simulation results very well. Simulations and model results for coalescence of drops in shear and gravitational field are also found to agree well, with substantial role of coalescence cascades on half life of these dispersions. We also show that in this work that addition of commercial grade hydrophobic and hydrophilic silica particles in size range of tens of microns destabilizes liquid-liquid dispersions even at extremely small concentrations, as small as 0.05% by volume. Conductivity of agitated dispersion is measured at high sampling rates to understand the mechanism of destabilisation. Studies show that near inversion, very large transiently connected domains of dispersed phase exist which offer significantly reduced interfacial area so as to increase the fractional interfacial area covered by particles.

Present work in aimed at understanding the hydrodynamics of flow in the annular centrifugal contactors using commercially available computational fluid dynamics software. Full scale simulations are carried out for three different multi-phase problems using volume of fluid (VOF) method of tracking an interface and geo-reconstruct method to construct the interface. Flow field in a partially filled rotating cylinder, closed at the bottom and open at the top, is investigated under no net upward flow condition. The widely known solution of this problem, with no interaction permitted between the liquid and the gas phase, leads to parabolic shape of the interface and solid body like rotation of the liquid at steady state. When interaction is permitted between the two phases in full scale simulation, we find that gas is sucked into the cylinder from the inner region of the open top. It travels downward, changes direction, moves up along the gas-liquid interface and is expelled out from the outer region of the open top. The gas going up along the interface drags liquid with it. The liquid present in the vicinity of the solid wall also climbs up. Both the liquid streams climbing up join at the top and move down along the interface. The 2D axisymmetric simulations thus predict the presence of two circulation loops in liquid, and gas entering from the inner region of the open top and escaping from the peripheral region. Simulations were also carried out for three phase system: carbon tetrachloride-water-air. The air-water interface behaved the same way as in the previous case. The simulations were next carried with liquid entering from the bottom and leaving the top, as in pumping mode. Simulations show that angular momentum of the incoming liquid significantly influences the shape of the gas-liquid interface and the maximum pumping capacity of a rotor. The traces of recirculation loops observed in the liquid phase for no upward flow case are seen with net upward flow case as well. The effect of height of baffles located below the rotor on hydrodynamics of flow through the annular zone, investigated experimentally and computationally earlier in the group, was re examined. In these experiments, critical rotational speed was measured for various baffle heights, annular gaps, and gap below the rotor for no net flow and a fixed steady state liquid height in the annular zone. The simulations carried out earlier with the assumption of flat interface in the annular region captured the dependence of critical angular speed on various parameters except the height of baffles. These simulations were repeated in this work with VOF method so as to compute the shape of the interface as part of the simulations. The predictions showed significant improvement in agreement for one baffle height but none for another case.

The design and control of microstructural evolution is the key to the processing of materials ranging from semiconductors to metals to polymers. In the case of crystalline silicon and its alloys, which are commonly used in the microelectronics industry, nucleation and aggregation of point defects and impurities are responsible for the formation of a wide variety of nano- and microstructures. While these microstructures often are detrimental to electronic devices, they can also be useful if their formation can be precisely controlled. The aim of my work was to develop a quantitative and mechanistic understanding of atomic scale aggregation processes in solids with emphasis on defect evolution in silicon.
In the first part of my talk, I present a multiscale "internally consistent modeling framework" designed to study aggregation in crystalline materials. The key component of this method is a parametrically consistent comparison between atomistic and continuum representation of the aggregation process, in which all parameters needed for the continuum model are derived from the same interatomic potential used to generate the atomistic aggregation data. This consistency allows for the direct probing of the mechanistic accuracy of the continuum rate equations without any ambiguity in the input parameters. The results demonstrate that existing models of vacancy cluster aggregation exclude important dynamic and structural effects that enhance the aggregation rate by providing additional aggregation pathways.
In the second part of my talk, I present a new method for extending the scope of molecular dynamics simulations of clustering in crystals. The method is referred to as "Feature Activated Molecular Dynamics" or FAMD. FAMD exploits the local nature of lattice disturbances around certain types of defects and is shown to greatly reduce the computational burden associated with MD simulation of aggregation. The computational cost of this method is shown to scale linearly with the number of defect entities simulated and not with the overall size of the system. The method is shown to be useful in several different applications beyond homogeneous nucleation.
The modeling and simulation schemes developed in my work exemplify the growing trend in area of materials research - consistent exchange of mechanistic and parametric information across multiple scales, from nanoscale, to microscale, to macro (process) scale. This approach has led to more fundamental understanding of materials physics along with improved efficiencies in the existing technologies and development of new ones.

Surface modification by adsorption of surfactant molecules has a wide range of technological applications such as mineral flotation, nanotribology, detergency and corrosion inhibition. It is important to understand the microstructure and kinetics of film evolution on the surface in order to develop modified surfaces for a desired application. The first part of my talk is concerned with the time evolution of multilayer film thickness measurements and domain formation of octadecylamine molecules adsorbed on a mica surface using atomic force microscopy (AFM) and FTIR spectroscopy. The adsorbed film thickness is determined by measuring the height profile across the mica-amine interface of a mica surface partially immersed in an amine solution. Adsorption of amine on mica is found to occur in three distinct stages with morphologically distinct domain formation and growth occurring during each stage. In the first stage (< 60 s), adsorption is primarily in the monolayer regime. The second stage which occurs between 60- 300 s, is associated with a regime of rapid film growth, and the film thickness changes from about 1.25 nm to 25 nm. Further exposure to the amine solution results in an increase in the domain size and a regime of lateral domain growth is observed. The time evolution of the film growth has been modelled by solving the diffusion equation with a two site Langmuir isotherm. The model quantitatively captures the time at which the thin to thick film transition occurs as well as the time required for complete film growth at longer times. The Ward-Tordai equation is also solved to determine the model parameters in the monolayer adsorption regime which occurs during the initial stages of film growth. The effect of kinetic as well as equilibrium parameters on the film evolution will be discussed. In the last part of my talk I will focus on the influence of surface modification of highly oriented pyrolytic graphite (HOPG) carbon-carbon interactions. The interactions were studied by measuring the pull-off forces between the treated HOPG and diamond like carbon AFM probes. Results show that these forces are not sensitive to relative humidity up to 55%. The study also illustrates that the pull-off forces increase with the immersion temperature of the hexadecane bath used for treating the HOPG.