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ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞),... more
ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞), is calculated as a function of an appropriately chosen dimensionless time, permitting expression of the height-time dependence as a function of the reciprocal of the exponent in the power-law model, s = 1/n. It is found that the rate of penetration and, therefore, also withdrawal of liquid is dramatically retarded as the liquid becomes more strongly shear-thinning, i.e., as n becomes small relative to unity.
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The structure of hydrogen chloride (dimer, crystal lattice and liquid) has been calculated using an intermolecular potential model that consists of a central Lennard-Jones (12, 6) part, a polarizable dipole and a permanent quadrupole.... more
The structure of hydrogen chloride (dimer, crystal lattice and liquid) has been calculated using an intermolecular potential model that consists of a central Lennard-Jones (12, 6) part, a polarizable dipole and a permanent quadrupole. Good agreement with available experimental data and quantum mechanical results is obtained for all three structures. In addition the potential model gives satisfactory results for the pressure second virial coefficient. Previous potential models for HCl have been unable to reproduce the liquid structure very accurately.
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Molecular simulations using the method of molecular dynamics have been carried out to determine if external fields can be used to increase the efficiency of membrane-based separation processes, examining both direct and several... more
Molecular simulations using the method of molecular dynamics have been carried out to determine if external fields can be used to increase the efficiency of membrane-based separation processes, examining both direct and several alternating electric fields, and across a range of frequencies. The results show that alternating electric fields have considerable promise as a valuable, yet generally neglected, tool for
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... 7. S. Murad, P. Ravi and JG Powles, J. Chem. Phys., 98 (1993) 9971. 8. S. Murad and JG Powles, J. Chem. Phys., 99 (1993) 7271. 9. S. Murad, Adsorption, 2 (1996) 95; F. Paritosh and S. Murad, AIChE J., 42 (1996) 2984. 10. ...
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A novel computer simulation technique for studying fluids in confined geometries has been developed and used to replicate Pfeffer’s experiment on osmosis in semipermeable membranes in 1877. Our results confirm the validity of van’t Hoff’s... more
A novel computer simulation technique for studying fluids in confined geometries has been developed and used to replicate Pfeffer’s experiment on osmosis in semipermeable membranes in 1877. Our results confirm the validity of van’t Hoff’s famous relationship for osmotic pressure over a wide range of concentrations, and also clearly establish its validity even for molecular systems. We believe this is the first theoretical validation of this result for such a wide range of concentrations, where no explicit assumption of ideality is made for the interactions of the solute molecules.
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The effect of external electric fields on enhancing ion mobility, drift velocity, and drift diffusion as a function of solution concentration has been investigated using molecular dynamics simulations. Our results show that the unusual... more
The effect of external electric fields on enhancing ion mobility, drift velocity, and drift diffusion as a function of solution concentration has been investigated using molecular dynamics simulations. Our results show that the unusual nonlinear behavior observed when the solution concentration matches seawater is also observed when the concentration is reduced to half of that value. These results are of significance in designing processes for desalinating seawater using electro-deionization in which the concentration would decrease during salt removal, and for purification of brackish waters which also have lower salt content.
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We present a simple molecular dynamics (MD)-based method for determining the Henry’s constant and gas-solubility in liquids and have applied it to the case of oxygen dissolved in liquid benzene. This method is an extension of an algorithm... more
We present a simple molecular dynamics (MD)-based method for determining the Henry’s constant and gas-solubility in liquids and have applied it to the case of oxygen dissolved in liquid benzene. This method is an extension of an algorithm we presented earlier to study osmosis and reverse osmosis in liquid solutions and gaseous mixtures. It is based on separating a gaseous
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Molecular simulations using the method of molecular dynamics have been carried out to examine the role that external magnetic fields can play in the transport of water via reverse osmosis (RO) across membranes. Our results show that... more
Molecular simulations using the method of molecular dynamics have been carried out to examine the role that external magnetic fields can play in the transport of water via reverse osmosis (RO) across membranes. Our results show that magnetic fields can increase the transport rate of water across such membranes significantly. These observations can have an important impact on making RO separation processes that involve the removal of water from solutions more efficient, since low flux rates across membranes is an important problem encountered in most current RO processes. We are aware of no experimental studies of such effects.
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ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞),... more
ABSTRACT The penetration rate of power-law non-Newtonian liquids in a circular tube driven by the capillary pressure is derived. The dimensionless fractional height of liquid in the tube relative to the equilibrium height, χ = h(t)/h(∞), is calculated as a function of an appropriately chosen dimensionless time, permitting expression of the height-time dependence as a function of the reciprocal of the exponent in the power-law model, s = 1/n. It is found that the rate of penetration and, therefore, also withdrawal of liquid is dramatically retarded as the liquid becomes more strongly shear-thinning, i.e., as n becomes small relative to unity.
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Page 1. PINSTECH/NPD-124 MOLECULAR DYNAMICS! APPLICATION TO LIQUID SODIUM Kbawaja Yaldram Abdullah Sadiq Sohail Murad li ( ii I tk > >\ ! ? 1 ! I / \ ! j I ! ! il: M; NUCLEAR PHYSICS DIVISION Pakistan Institute ...
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Molecular dynamics simulations have been used to investigate the effect of confinement on solvation (hydration shell) and solubility of electrolyte solutions (NaCl) confined in nanopores. The co-ordination number and solubility of NaCl in... more
Molecular dynamics simulations have been used to investigate the effect of confinement on solvation (hydration shell) and solubility of electrolyte solutions (NaCl) confined in nanopores. The co-ordination number and solubility of NaCl in water confined in graphitic slit nanopores ...
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... 20 m sl, and droplet size about 5 nm is shown in figure 2. It is seen that the droplets move closer to each other until about 40 000 timesteps, corresponding roughtly to 340ps, and then begin to show signs of bouncing back. After ...
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... This was also in part financed by UKC. Finally, we thank Mr AD Smith and Mr JBWWebber for advice and assistance in the installation and operation of the computer system. References [1] RAHMAN, A., 1964, Phys. Rev. A, 136, 405. ...
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Using molecular simulations, we have investigated heat transfer across the solid–fluid interface of a silica wafer in contact with water vapor. Our results show that the thermal or Kapitza resistance decreases significantly, as the... more
Using molecular simulations, we have investigated heat transfer across the solid–fluid interface of a silica wafer in contact with water vapor. Our results show that the thermal or Kapitza resistance decreases significantly, as the surface becomes more hydrophilic. This is primarily due to increases in adsorption and absorption at the surface, which enhances the intermolecular collision frequency at the interface. Increasing this frequency also reduces the dependence of thermal transport on variations in the interfacial temperature and ...
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Gas separations with faujasite zeolite membranes have been examined using the method of molecular dynamics. Two binary mixtures are investigated, oxygen/nitrogen and nitrogen/carbon dioxide. These mixtures have been found experimentally... more
Gas separations with faujasite zeolite membranes have been examined using the method of molecular dynamics. Two binary mixtures are investigated, oxygen/nitrogen and nitrogen/carbon dioxide. These mixtures have been found experimentally to exhibit contrasting behavior. In O2/N2 mixtures the ideal selectivity (pure systems) is higher than the mixture selectivity, while in N2/CO2 the mixture selectivity is higher than the ideal selectivity. One of the key goals of this work was to seek a fundamental molecular level understanding of such divergent behavior. Our simulation results (using previously developed intermolecular models for both the gases and zeolites investigated) were found to replicate this experimental behavior. By examining the loading of the membranes and the diffusion rates inside the zeolites, we have been able to explain such contrasting behavior of O2/N2 and N2/CO2 mixtures. In the case of O2/N2 mixtures, the adsorption and loading of both O2 and N2 in the membrane are quite competitive, and thus the drop in the selectivity in the mixture is primarily the result of oxygen slowing the diffusion of nitrogen and nitrogen somewhat increasing the diffusion of oxygen when they pass through the zeolite pores. In N2/CO2 systems, CO2 is rather selectively adsorbed and loaded in the zeolite, leaving very little room for N2 adsorption. Thus although N2 continues to have a higher diffusion rate than CO2 even in the mixture, there are so few N2 molecules in the zeolite in mixtures that the selectivity of the mixture increases significantly compared to the ideal (pure system) values. We have also compared simulation results with hydrodynamic theories that classify the permeance of membranes to be either due to surface diffusion, viscous flow, or Knudsen diffusion. Our results show surface diffusion to be the dominant mode, except in the case of N2/CO2 binary mixtures where Knudsen diffusion also makes a contribution to N2 transport.
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CiteULike organises scholarly (or academic) papers or literature and provides bibliographic (which means it makes bibliographies) for universities and higher education establishments. It helps undergraduates and postgraduates. People... more
CiteULike organises scholarly (or academic) papers or literature and provides bibliographic (which means it makes bibliographies) for universities and higher education establishments. It helps undergraduates and postgraduates. People studying for PhDs or in postdoctoral ( ...
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Salt hydrates undergo desorption on being heated above certain charging temperatures, releasing water and forming anhydrous salts which have a higher energy content. Since these salts are hygroscopic, energy is easily retrieved back by... more
Salt hydrates undergo desorption on being heated above certain charging temperatures, releasing water and forming anhydrous salts which have a higher energy content. Since these salts are hygroscopic, energy is easily retrieved back by passing water vapor over the anhydrous form. Such a technique of energy conversion, storage and retrieval enables these salts to be impregnated into porous media for thermo-chemical energy application. However, to investigate the thermal transport at the interface of the porous material and the salt, atomistic ...
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Effective energy storage is one of the limitations of emerging renewable energy technologies. Solar and wind energy generation methods have proven to be capable of producing levels of energy that exceed immediate needs and the storage of... more
Effective energy storage is one of the limitations of emerging renewable energy technologies. Solar and wind energy generation methods have proven to be capable of producing levels of energy that exceed immediate needs and the storage of this excess energy often presents a problem. Redox flow batteries (RFBs) have become an attractive form of storage because of their safety, capacity, and small environmental footprint; however, this technology is not yet widely available due to inefficiencies in the ion-exchange membrane. The current technology widely utilizes polymeric membranes. These have stability problems in the highly reactive environment of the RFB and tend to break down, shortening the life of the battery. Also, they present less than desirable selectivity for proton transport which is crucial to the overall efficiency of the battery. It has been proposed that thin zeolite membranes will provide both the stability and selectivity to improve the performance of RFBs and make t...
The interaction of nanoparticle with cells and lipid membranes plays a critical role in the applications of nanoparticles for therapy, cellular image, biodiagnostics and drug delivery systems. It has been shown that such interactions and... more
The interaction of nanoparticle with cells and lipid membranes plays a critical role in the applications of nanoparticles for therapy, cellular image, biodiagnostics and drug delivery systems. It has been shown that such interactions and the deformation of lipid membranes are often determined by physicochemical properties of nanomaterials, such as size, shape and surface composition. Here, we carry out molecular dynamic simulations using various sizes of nanocrystals as a probe to explore the transport of nanomaterials across dipalmitoylphosphatidylcholine (DPPC). A Coarse-Grained model was used to provide insight at large time and length scales. The dynamics properties of the nanocrystals, as well as the structural properties of lipid membrane arising from the interaction between the nanocrystal and the lipid membrane are investigated. Our simulation results are in satisfactory agreement with available experimental. We found that the minimum pressure for penetrating the first layer...
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We report on molecular simulation studies of the ionic flow in the presence of charged carbon nanotubes. Our domain contains three species; viz. positively charged sodium ions, negatively charged chlorine ions and neutral water; and a... more
We report on molecular simulation studies of the ionic flow in the presence of charged carbon nanotubes. Our domain contains three species; viz. positively charged sodium ions, negatively charged chlorine ions and neutral water; and a pair of single-walled carbon nanotube electrodes. One of the nanotube is positively charged and the other is negatively charged. The system of 1024 atoms
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This paper focuses on the use of carbon nanotubes (CNT) for ion separation and encapsulation from a solution containing both positive and negatively charged ions. Metal ion separation from drinking water or during material processing... more
This paper focuses on the use of carbon nanotubes (CNT) for ion separation and encapsulation from a solution containing both positive and negatively charged ions. Metal ion separation from drinking water or during material processing applications can be an important issue. We ...
ABSTRACT Redox flow batteries (RFBs) have become an attractive form of energy storage because of their safety, capacity, and small environmental footprint; however, this technology is not yet widely available due to inefficiencies in the... more
ABSTRACT Redox flow batteries (RFBs) have become an attractive form of energy storage because of their safety, capacity, and small environmental footprint; however, this technology is not yet widely available due to inefficiencies in the ion-exchange membrane. The current technology widely utilizes polymeric membranes that have stability problems in the highly reactive environment of the RFB and tend to break down, shortening the life of the battery. Also, they present less than desirable selectivity for proton transport, which is crucial to the overall efficiency of the battery. It has been proposed that thin zeolite membranes will provide both the stability and the selectivity to improve the performance of RFBs and make their wide-scale application more feasible. A molecular dynamics study of six types of these membranes (ERI, LTA, MFI, BEC, CFI, DON) and the ions present in the vanadium-RFB has been undertaken to determine their transport behavior and investigate the molecular level requirements for their suitability for IEM applications. The hydration of the vanadium(II) [V2+], vanadium(III) [V3+], oxovanadium(IV) [VO2+], and dioxovanadium(V) [VO2+] ions plays a key part in ion transport and was examined in detail. Structures and dynamics of the hydration shells were investigated and found to agree with previously reported findings when available. Ion transport was observed with the BEC, CFI, and DON zeolite framework types and the dynamics/properties of this transport were studied. It was found that a relatively large pore (∼7 Å) was necessary for ion transport due to the strongly bound hydration shell that effectively increases the size of the ion. As the ions pass through the membrane, the shape and structure of their hydration shells remain unchanged. This verifies that the size of the hydrated ion complex is a key factor in zeolite membrane transport. The only ion transport observed through membranes with smaller pores (<5 Å) such as ERI, LTA, and MFI zeolite frameworks was that of the hydronium ion. Therefore, these membranes demonstrate the selective transport of hydronium ions over vanadium ions that is an essential requirement for IEMs in vanadium RFBs.
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ABSTRACT We have improved the estimation of the solubility of hydrogen and carbon monoxide in a range of linear alcohols and alkanes (between C4 and C32) by using the method of molecular dynamics (MD) together with experimental data and... more
ABSTRACT We have improved the estimation of the solubility of hydrogen and carbon monoxide in a range of linear alcohols and alkanes (between C4 and C32) by using the method of molecular dynamics (MD) together with experimental data and traditional thermodynamics analysis. The goal of the study was to use a fundamental molecular-based method, after validation, to fill gaps in data in current literature, especially for systems considered challenging for traditional measurement and estimation methods. The simulation system used semi-permeable membranes to mimic actual experimental studies of gas solubility. Our combined analysis of both data and simulation results demonstrated that for higher carbon numbers (CN) both CO and H2 individually have similar Henry’s constant values in the two solvents, with H2 values being roughly 50% higher in both solvents. The data and simulation results were also used to estimate limiting values of the mass-based Henry’s constant for H2 and CO in the higher alcohols (large CN).
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MFI zeolite coated optical fiber sensors have been developed for in situ detection of dissolved organics in water. The sensors operate by monitoring the optical reflectivity changes caused by the selective adsorption of organic molecules,... more
MFI zeolite coated optical fiber sensors have been developed for in situ detection of dissolved organics in water. The sensors operate by monitoring the optical reflectivity changes caused by the selective adsorption of organic molecules, i.e., 2-propanol or pentanoic acid in this study, from aqueous solutions in the zeolitic pores. Reversible and monotonic sensor signals were observed in response to the variation of 2-propanol concentration in water with fast response. However, the sensor exhibited a much slower response to pentanoic acid than to 2-propanol. It was also found that substitution of Si by Al in the MFI framework increased the adsorption of pentanoic acid that resulted in enhanced sensor responses.
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The contact resistance problem between dissimilar or bonded substrates is particularly important at the nanoscale, since the length scales associated with the structures and energy carriers become comparable. We provide a basic... more
The contact resistance problem between dissimilar or bonded substrates is particularly important at the nanoscale, since the length scales associated with the structures and energy carriers become comparable. We provide a basic understanding of nanoscale thermal properties, focusing on nanoscale composition and surface structure effects on local and bulk thermal properties, and discuss how surface modifications can create novel materials and structures that have tunable thermal properties. Since nanoscale flows are ...
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Micro- and macroscale investigations have shown that colliding drops always coalesce for small values of the Weber number We = rhoU2d/sigma. Our molecular dynamic simulations show that nanojets always recoil following head-on collision... more
Micro- and macroscale investigations have shown that colliding drops always coalesce for small values of the Weber number We = rhoU2d/sigma. Our molecular dynamic simulations show that nanojets always recoil following head-on collision even though We --> 0. The duration between collision and recoil is a function of the nanojet impact velocity Uo and the nature of intermolecular interactions. Evaporation, which promotes mixing, occurs during recoil and is enhanced by reducing intermolecular interactions. Thereafter, mixing occurs through diffusion. The mixing dynamics are independent of Uo and the orifice shape. Consistent with a continuum analysis, the characteristic nanojet diameter at stagnation ds,1 proportional to Uo, recoil time following collision tau proportional to Uo-2, and the number of evaporating molecules N proportional to Uo.
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The thermal conductivity of dense polyatomic fluid mixtures has been studied using the method of non-equilibrium molecular dynamics. Molecular mixtures of the type spherical-nonspherical and nonspherical-nonspherical, have been... more
The thermal conductivity of dense polyatomic fluid mixtures has been studied using the method of non-equilibrium molecular dynamics. Molecular mixtures of the type spherical-nonspherical and nonspherical-nonspherical, have been investigated. In addition, we have examined the contribution to thermal conductivity from internal rotational modes. Internal rotational contributions are needed for predicting thermal conductivity of polyatomics. Our results combined with those we obtained for pure polyatomics, have shown that the usual approximation made in theories, that these contributions are density independent is incorrect. Finally, we have also developed an approximate method for predicting internal contributions to thermal conductivity, that includes density dependence.
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... G. The NosC-Hoover ... discussion on their interpretation is given, for example, in: JV Sengers and J. Luettmer-Strathmann, The Critical Enhancements in Transport properties of Fluids: Their Correlation, Prediction and Estimation... more
... G. The NosC-Hoover ... discussion on their interpretation is given, for example, in: JV Sengers and J. Luettmer-Strathmann, The Critical Enhancements in Transport properties of Fluids: Their Correlation, Prediction and Estimation (J. Millat, J . H. Dymond, and CA Nieto de Castro ...
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Using molecular simulations, we have investigated heat transfer across the solid–fluid interface between water and silicon and silica wafers, and solid–solid interfaces in superlattices and thin solid films. The system set-up has allowed... more
Using molecular simulations, we have investigated heat transfer across the solid–fluid interface between water and silicon and silica wafers, and solid–solid interfaces in superlattices and thin solid films. The system set-up has allowed us to focus on the resistance associated with both the fluid and solid interfaces. For instance, by maintaining the solid phase at a constant temperature we can focus solely on the fluid-side resistance. Our results show that the thermal or Kapitza resistance at fluid side of the solid–fluid ...
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The pervaporation separation of liquid mixtures of water/ethanol and water/methanol using three zeolite (Silicalite, NaA and Chabazite) membranes has been examined using the method of molecular dynamics. The main goal of this study was to... more
The pervaporation separation of liquid mixtures of water/ethanol and water/methanol using three zeolite (Silicalite, NaA and Chabazite) membranes has been examined using the method of molecular dynamics. The main goal of this study was to identify intermolecular interactions between water, methanol, ethanol and the membrane surface that play a critical role in the separations. This would then allow better membranes
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Time correlation functions for liquid ammonia using an intermolecular potential model developed recently (Mansour and Murad, 1987) are reported. The potential model which consists of a Lennard-Jones central part, a point dipole and... more
Time correlation functions for liquid ammonia using an intermolecular potential model developed recently (Mansour and Murad, 1987) are reported. The potential model which consists of a Lennard-Jones central part, a point dipole and quadrupole and dipole polarizability (multi-body) has been found (Mansour and Murad 1987) to give an accurate representation of many measured thermodynamic and transport properties. The properties reported
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Molecular simulations using the method of molecular dynamics have been carried out to study the dynamics and energetics of ion exchanges between monovalent and bivalent cations in supercritical and subcritical (liquid) electrolyte... more
Molecular simulations using the method of molecular dynamics have been carried out to study the dynamics and energetics of ion exchanges between monovalent and bivalent cations in supercritical and subcritical (liquid) electrolyte solutions (here Li+, and Ca++ in aqueous solutions of LiCl and CaCl2) and an ion exchange membrane (NaA zeolite) using direct simulations of up to a nanosecond or
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Biological membranes are one of the major structural elements of cells, and play a key role as a selective barrier and substrate for many proteins that facilitate transport and signaling processes. Understanding the structural and... more
Biological membranes are one of the major structural elements of cells, and play a key role as a selective barrier and substrate for many proteins that facilitate transport and signaling processes. Understanding the structural and mechanical properties of lipid membranes during permeation of nanomaterials is of prime importance in determining the toxicity of nanomaterials to living cells. It has been shown that the interaction between lipid membranes and nanomaterials and the disruption of lipid membranes are often determined by physicochemical properties of nanomaterials, such as size, shape and surface composition. In this work, molecular dynamic simulations were carried out using various sizes of nanocrystals as a probe to explore the transport of nanomaterials across dipalmitoylphosphatidylcholine (DPPC) bilayers and the changes in the structural and mechanical properties of DPPC bilayers during the permeation. A coarse-grained model was used to provide insight at large time and length scales. In this work, an external driving force helps the nanocrystals across the lipid bilayer. The minimum forces needed to penetrate the model membrane and the interaction of nanocrystals and lipid bilayers were investigated in simulations. The elastic and dynamic properties of lipid bilayers, including the local and bulk properties during the permeation of the nanocrystals, which are of considerable fundamental interest, were also studied. The findings described will lead to better understanding of nanomaterial–lipid membrane interactions and the mechanical and dynamic properties of lipid membranes under permeation.
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1. INTRODUCTION The success of modelling monatomic fluids by molecular dynamics methods led to attempts to simulate rigid polyatomics. This was done by solving either Hamilton's, Lagrange's or Euler's equations of motion... more
1. INTRODUCTION The success of modelling monatomic fluids by molecular dynamics methods led to attempts to simulate rigid polyatomics. This was done by solving either Hamilton's, Lagrange's or Euler's equations of motion using Euler angles to represent the orientations. It was ...
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How nanoparticles interact with biological membranes is of significant importance in determining the toxicity of nanoparticles as well as their potential applications in phototherapy, imaging and gene/drug delivery. It has been shown that... more
How nanoparticles interact with biological membranes is of significant importance in determining the toxicity of nanoparticles as well as their potential applications in phototherapy, imaging and gene/drug delivery. It has been shown that such interactions are often determined by nanoparticle physicochemical factors such as size, shape, hydrophobicity and surface charge density. Surface modification of the nanoparticle offers the possibility of
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MFI zeolite coated optical fiber sensors have been developed for in situ detection of dissolved organics in water. The sensors operate by monitoring the optical reflectivity changes caused by the selective adsorption of organic molecules,... more
MFI zeolite coated optical fiber sensors have been developed for in situ detection of dissolved organics in water. The sensors operate by monitoring the optical reflectivity changes caused by the selective adsorption of organic molecules, i.e., 2-propanol or pentanoic acid in this study, from aqueous solutions in the zeolitic pores. Reversible and monotonic sensor signals were observed in response to the variation of 2-propanol concentration in water with fast response. However, the sensor exhibited a much slower response to pentanoic acid than to 2-propanol. It was also found that substitution of Si by Al in the MFI framework increased the adsorption of pentanoic acid that resulted in enhanced sensor responses.
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Data for the viscosity and thermal conductivity coefficients of ethane have been evaluated and represented by an empirical function. Tables of values have been prepared for the range 200-500 K, for pressure to 75 MPa (about 750 atm). The... more
Data for the viscosity and thermal conductivity coefficients of ethane have been evaluated and represented by an empirical function. Tables of values have been prepared for the range 200-500 K, for pressure to 75 MPa (about 750 atm). The tables include an estimate of the anomalous contribution to the thermal conductivity in the neighborhood of the critical point. The estimated uncertainties of the tabular values are + or - 5% and + or - 8% for the viscosity and thermal conductivity coefficient, respectively.
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Computer simulation studies have been carried out, using a novel method, to examine the behavior of fluids in various confined geometries, including, slit pores, square and cylindrical tubular pores, cubic pores, and pores with rough... more
Computer simulation studies have been carried out, using a novel method, to examine the behavior of fluids in various confined geometries, including, slit pores, square and cylindrical tubular pores, cubic pores, and pores with rough walls. The method used to model these pores allows for the permeability of the pore wall to the confined fluid to be controlled precisely between the impermeable and totally permeable limits, while at the same time maintaining the atomic nature of the pore wall. These systems have been studied with several models for the pore wall for a wide range of state conditions. The results obtained for nonuniform density distributions, wall permeabilities, and diffusion coefficients are examined in detail.
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Gas separation efficiencies of three zeolite membranes (Faujasite, MFI, and Chabazite) have been examined using the method of molecular dynamics. Our investigation has allowed us to study the effects of pore size and structure, state... more
Gas separation efficiencies of three zeolite membranes (Faujasite, MFI, and Chabazite) have been examined using the method of molecular dynamics. Our investigation has allowed us to study the effects of pore size and structure, state conditions, and compositions on the permeation of two binary gas mixtures, O(2)N(2) and CO(2)N(2). We have found that for the mixture components with similar sizes and adsorption characteristics, such as O(2)N(2), small-pore zeolites are not suited for separations, and this result is explicable at the molecular level. For mixture components with differing adsorption behavior, such as CO(2)N(2), separation is mainly governed by adsorption and small-pore zeolites separate such gases quite efficiently. When selective adsorption takes place, we have found that, for species with low adsorption, the permeation rate is low, even if the diffusion rate is quite high. Our results further indicate that loading (adsorption) dominates the separation of gas mixtures in small-pore zeolites, such as MFI and Chabazite. For larger-pore zeolites such as Faujasite, diffusion rates do have some effect on gas mixture separation, although adsorption continues to be important. Finally, our simulations using existing intermolecular potential models have replicated all known experimental results for these systems. This shows that molecular simulations could serve as a useful screening tool to determine the suitability of a membrane for potential separation applications.
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Gas separations with faujasite zeolite membranes have been examined using the method of molecular dynamics. Two binary mixtures are investigated, oxygen/nitrogen and nitrogen/carbon dioxide. These mixtures have been found experimentally... more
Gas separations with faujasite zeolite membranes have been examined using the method of molecular dynamics. Two binary mixtures are investigated, oxygen/nitrogen and nitrogen/carbon dioxide. These mixtures have been found experimentally to exhibit contrasting behavior. In O(2)/N(2) mixtures the ideal selectivity (pure systems) is higher than the mixture selectivity, while in N(2)/CO(2) the mixture selectivity is higher than the ideal selectivity. One of the key goals of this work was to seek a fundamental molecular level understanding of such divergent behavior. Our simulation results (using previously developed intermolecular models for both the gases and zeolites investigated) were found to replicate this experimental behavior. By examining the loading of the membranes and the diffusion rates inside the zeolites, we have been able to explain such contrasting behavior of O(2)/N(2) and N(2)/CO(2) mixtures. In the case of O(2)/N(2) mixtures, the adsorption and loading of both O(2) and N(2) in the membrane are quite competitive, and thus the drop in the selectivity in the mixture is primarily the result of oxygen slowing the diffusion of nitrogen and nitrogen somewhat increasing the diffusion of oxygen when they pass through the zeolite pores. In N(2)/CO(2) systems, CO(2) is rather selectively adsorbed and loaded in the zeolite, leaving very little room for N(2) adsorption. Thus although N(2) continues to have a higher diffusion rate than CO(2) even in the mixture, there are so few N(2) molecules in the zeolite in mixtures that the selectivity of the mixture increases significantly compared to the ideal (pure system) values. We have also compared simulation results with hydrodynamic theories that classify the permeance of membranes to be either due to surface diffusion, viscous flow, or Knudsen diffusion. Our results show surface diffusion to be the dominant mode, except in the case of N(2)/CO(2) binary mixtures where Knudsen diffusion also makes a contribution to N(2) transport.
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We present a technique for estimating intermolecular potential model parameters for polar compounds. This technique has been used for two polar compounds, hydrogen chloride and ammonia. The potential models are then used to study a wide... more
We present a technique for estimating intermolecular potential model parameters for polar compounds. This technique has been used for two polar compounds, hydrogen chloride and ammonia. The potential models are then used to study a wide range of static and dynamic properties using computer simulations. Where possible, results have been compared with experimental data to demonstrate the adequacy of the models. Static properties have been calculated using the methods of Monte Carlo and equilibrium molecular dynamics. The shear viscosity has been obtained using the nonequilibrium molecular dynamics method. Finally, we also report results for a computer simulation study of quadrupolar mixtures. This study investigates the changes in properties caused by a change in the sign of the quadrupole moment of one mixture component.
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Using the method of molecular dynamics (MD), we have estimated the solubility of hydrogen in heavy hydrocarbons for a range of temperatures and pressures. Heavy hydrocarbon systems are known to be challenging not only for experimental... more
Using the method of molecular dynamics (MD), we have estimated the solubility of hydrogen in heavy hydrocarbons for a range of temperatures and pressures. Heavy hydrocarbon systems are known to be challenging not only for experimental measurements but also for reliable estimations using traditional equations of state (EOS). The simulation system used was designed with semi-permeable membranes to mimic actual
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... atoms, except that they are not so free to move and provided one does not try to go among them, as is unnecessary for D. In stark contrast the ... 1. D. Nicholson and NG Parsonage Computer simulation and the statistical mechanics of... more
... atoms, except that they are not so free to move and provided one does not try to go among them, as is unnecessary for D. In stark contrast the ... 1. D. Nicholson and NG Parsonage Computer simulation and the statistical mechanics of adsorption, Academic Press, New York (1982 ...
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... The results show thai even strong non axial quadrupolar interactions do not cause any significant anisoiropy in F2) or T2 . ... References 11] CG Gray. KE Gubbins, S. Murad and KS String, Chem. Phys. Letters 95 (1983) 541, [2] KE... more
... The results show thai even strong non axial quadrupolar interactions do not cause any significant anisoiropy in F2) or T2 . ... References 11] CG Gray. KE Gubbins, S. Murad and KS String, Chem. Phys. Letters 95 (1983) 541, [2] KE Gubbins, CG Gray and JRS Maehado, Mol. ...
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Using molecular simulations, we have investigated heat transfer across the solid–fluid interface of a silica wafer in contact with water vapor. Our results show that the thermal or Kapitza resistance decreases significantly, as the... more
Using molecular simulations, we have investigated heat transfer across the solid–fluid interface of a silica wafer in contact with water vapor. Our results show that the thermal or Kapitza resistance decreases significantly, as the surface becomes more hydrophilic. This is primarily due to increases in adsorption and absorption at the surface, which enhances the intermolecular collision frequency at the interface. Increasing this frequency also reduces the dependence of thermal transport on variations in the interfacial temperature and ...
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... R., and King AD, "Effect of Pressure on the Surface Tension of n-Hexane", J. Phys. Chem., 79, 1676 (1975). 8. Mollerup JS, Adu. Cryogcn. Engrg., "Correlated and Predicted Thermodynamic Properties of LNG and... more
... R., and King AD, "Effect of Pressure on the Surface Tension of n-Hexane", J. Phys. Chem., 79, 1676 (1975). 8. Mollerup JS, Adu. Cryogcn. Engrg., "Correlated and Predicted Thermodynamic Properties of LNG and Related Mixtures", 21, 1 (1976). 9. Murad S. "Generalized ...
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Abstract Using molecular dynamics, we consider the thermal resistances of superlattices consisting of varying numbers of distinct nanolayers of two different materials. These are placed between two water reservoirs at uniform hot and cold... more
Abstract Using molecular dynamics, we consider the thermal resistances of superlattices consisting of varying numbers of distinct nanolayers of two different materials. These are placed between two water reservoirs at uniform hot and cold temperatures. The interfacial resistances produced between different solid layers can lead to significantly lower heat transfer for a specified temperature difference. Such a large reduction in thermal transport cannot be explained by the interfacial resistance alone. In addition to the interfacial ...
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Abstract An organized nonuniform mass distribution in solids leads to a monotonically varying thermal conductivity in a nanomaterial so that the heat flux is directionally dependent. We investigate through molecular dynamics simulations... more
Abstract An organized nonuniform mass distribution in solids leads to a monotonically varying thermal conductivity in a nanomaterial so that the heat flux is directionally dependent. We investigate through molecular dynamics simulations if the influence of an organized mass distribution in a fluid also leads to thermal rectification. Heat transfer is monitored in a water reservoir placed between two (hot and cold) silicon walls. The distribution of the fluid in the reservoirs is organized by applying an external force to each ...
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We report on molecular simulation studies of the ionic flow in the presence of charged carbon nanotubes. Our domain contains three species; viz. positively charged sodium ions, negatively charged chlorine ions and neutral water; and a... more
We report on molecular simulation studies of the ionic flow in the presence of charged carbon nanotubes. Our domain contains three species; viz. positively charged sodium ions, negatively charged chlorine ions and neutral water; and a pair of single-walled carbon nanotube ...
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Salt hydrates undergo desorption on being heated above certain charging temperatures, releasing water and forming anhydrous salts which have a higher energy content. Since these salts are hygroscopic, energy is easily retrieved back by... more
Salt hydrates undergo desorption on being heated above certain charging temperatures, releasing water and forming anhydrous salts which have a higher energy content. Since these salts are hygroscopic, energy is easily retrieved back by passing water vapor over the anhydrous form. Such a technique of energy conversion, storage and retrieval enables these salts to be impregnated into porous media for thermo-chemical energy application. However, to investigate the thermal transport at the interface of the porous material and the salt, atomistic ...
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The Xe nuclear magnetic resonance chemical shift differences that afford the discrimination between various biological environments are of current interest for biosensor applications and medical diagnostic purposes. In many such... more
The Xe nuclear magnetic resonance chemical shift differences that afford the discrimination between various biological environments are of current interest for biosensor applications and medical diagnostic purposes. In many such environments the Xe signal appears close to that in water. We calculate average Xe chemical shifts (relative to the free Xe atom) in solution in eleven liquids: water, isobutane, perfluoro-isobutane, n-butane, n-pentane, neopentane, perfluoroneopentane, n-hexane, n-octane, n-perfluorooctane, and perfluorooctyl bromide. The latter is a liquid used for intravenous Xe delivery. We calculate quantum mechanically the Xe shielding response in Xe-molecule van der Waals complexes, from which calculations we develop Xe (atomic site) interpolating functions that reproduce the ab initio Xe shielding response in the complex. By assuming additivity, these Xe-site shielding functions can be used to calculate the shielding for any configuration of such molecules around Xe....