Biomedical subjects

N R Aluru

Publications and source records attributed to N R Aluru.

7 recordsLinked to original sources

PubMed2006

Hierarchical multiscale simulation of electrokinetic transport in silica nanochannels at the point of zero charge.

Effects of nanoscale confinement and partial charges that stem from quantum calculations are investigated in silica slit channels filled with 1 M KCl at the point of zero charge by using a hierarchical multiscale simulation methodology. Partial charges of both bulk and surface atoms from ab initio quantum calculations that take into account bond polarization and electronegativity are used in molecular dynamics (MD) simulations to obtain ion and water concentration profiles for channel widths of 1.1, 2.1, 2.75, and 4.1 nm. The interfacial electron density profiles of simulations matched well with that of recent X-ray reflectivity experiments. By simulating corresponding channels with no partial charges, it was observed that the partial charges affect the concentration profiles and transport properties such as diffusion coefficients and mobilities up to a distance of about 3 sigma(O)(-)(O) from the surface. Both in uncharged and partially charged cases, oscillations in concentration profiles of K(+) and Cl(-) ions give rise to an electro-osmotic flow in the presence of an external electric field, indicating the presence of an electric double layer at net zero surface charge, contrary to the expectations from classical continuum theory. I-V curves in a channel-bath system using ionic mobilities from MD simulations were significantly different for channels with and without partial charges for channel widths less than 4.1 nm.

Chlorides↗

PubMed2006

Effect of quantum partial charges on the structure and dynamics of water in single-walled carbon nanotubes.

In this work, using quantum partial charges, computed from 6-31G(**)B3LYP density functional theory, in molecular dynamics simulations, we found that water inside (6,6) and (10,0) single-walled carbon nanotubes with similar diameters but with different chiralities has remarkably different structural and dynamical properties. Density functional calculations indicate that tubes with different chiralities have significantly different partial charges at the ends of tubes. The partial charges at the ends of a (10,0) tube are around 4.5 times higher than those of a (6,6) tube. Molecular dynamics simulations with the partial charges show different water dipole orientations. In the (10,0) tube, dipole vectors of water molecules at the end of the tube point towards the water reservoir resulting in the formation of an L defect in the center region. This is not observed in the (6,6) tube where dipole vectors of all the water molecules inside the tube point towards either the top or the bottom water reservoir. The water diffusion coefficient is found to increase in the presence of the partial charges. Water in the partially charged (10,0) tube has a lower diffusion coefficient compared to that of in the partially charged (6,6) tube.

Computer Simulation↗

PubMed2006

Molecular understanding of osmosis in semipermeable membranes.

We investigate single-file osmosis of water through a semipermeable membrane with an uncharged, a positively and a negatively charged nanopore. Molecular dynamics simulations indicate that the osmotic flux through a negatively charged pore (J_) is higher compared to the osmotic flux in a positively charged pore (J+) followed by the osmotic flux in the uncharged pore (J(0)), i.e., J_ > J+ > J(0). The molecular mechanisms governing osmosis, steady state osmosis, and the observed osmotic flux dependence on the nanopore charge are explained by computing all the molecular interactions involved and identifying the molecular interactions that play an important role during and after osmosis. This study helps in a fundamental understanding of osmosis and in the design of advanced nanoporous membranes for various applications of osmosis.

Computer Simulation↗

PubMed2006

Differential ion transport induced electroosmosis and internal recirculation in heterogeneous osmosis membranes.

Water and ion transport through a heterogeneous membrane separating two electrolyte solutions at different concentrations is investigated by using molecular dynamics simulations. The membrane features pairs of oppositely charged pores with identical diameters. Simulation results indicate that the differential transport of K(+) and Cl(-) ions through the membrane pores creates an electrical potential difference across the membrane, which then induces an electroosmotic water flux. The induced electroosmosis creates an internal recirculation loop of water between adjacent pores. The implications of these new observations are discussed.

Chlorides↗

PubMed2005

Scaling of electrokinetic transport in nanometer channels.

Electrokinetic transport is a popular transport mechanism used in nanofluidic systems, and understanding its scaling behavior is important for the design and optimization of nanofluidic devices. In this article, we report on the scaling of electroosmotic flow and ionic conductivity in positively charged slit nanochannels by using continuum and atomistic simulations. The effects of confinement and surface charge are discussed in detail. In particular, we found that the viscosity of the interfacial water increases substantially as the surface charge density increases and the electrophoretic mobility of the interfacial ions decreases. We show that such effects can influence the scaling of the electrokinetic transport in confined nanochannels significantly.

Journal Article↗

PubMed2005

Complex oscillations and chaos in electrostatic microelectromechanical systems under superharmonic excitations.

In this Letter, the formation of complex oscillations of the type 2n M oscillations per period at the Mth superharmonic excitation is reported for electrostatic microelectromechanical systems. A dc bias (beyond "dc symmetry breaking") and an ac signal (at the Mth superharmonic frequency) with an amplitude around "ac symmetry breaking" gives rise to M oscillations per period or period M response. On increasing the ac voltage, a cascade of period doubling bifurcations take place giving rise to 2n M oscillations per period. An interesting chaotic transition (1-band and 2-band chaos) is observed during the first period doubling bifurcation. The nonlinear nature of the electrostatic force is shown to be responsible for the reported observations.

Journal Article↗

PubMed2004

Charge inversion and flow reversal in a nanochannel electro-osmotic flow.

Ion distribution and velocity profiles for electro-osmotic flow in a 3.49 nm wide slit channel with a surface charge density of -0.285 C/m(2) are studied using molecular dynamics simulations. Simulation results indicate that the concentration of the co-ion exceeds that of the counterion in the region 0.53 nm away from the channel wall, and the electro-osmotic flow is in the opposite direction to that predicted by the classical continuum theory. The charge inversion is mainly caused by the molecular nature of water and ions. The flow reversal is caused by the immobilization of counterions adsorbed on the channel wall and due to the charge inversion phenomena.

Journal Article↗