Modeling transport and filtration of nanoparticle suspensions in porous media.

Recently membrane filters have gained in significance due to the need to provide protection against airborne pollution. A question of importance, and some controversy, is the efficiency of filters for small nanoparticles with diameters below 100 nm as these are considered particularly dangerous due to possible penetration into the lungs. The efficiency is measured by the number of particles blocked by the pore structure after passing though the filter.

Normal mode analysis of a model semirigid polymer.

Dynamic and structural properties of biological polymers are important to their function but it is difficult to obtain information on molecular flexibility at an atomic level. This paper describes how a normal mode analysis can be used to describe the equilibrium and nonequilibrium properties of complex polymer systems such as DNA in solution. A weak coupling between the chain deformation and the local chain orientation simplifies the calculations.

Translocation of a stiff polymer in a microchannel.

The voltage-driven dynamics of a stiff polymer through a nanopore are treated with a bend elastic model. In contrast to flexible polymers described by a stretch elasticity, bend elastic chains can be oriented in an external field, here the anchoring field created by the pore atoms. The trajectory of the chain is calculated using the Langevin equation of motion.

Transport theory at the nanoscale. II. Interface dynamics for film growth.

Conditions for surface nucleation and growth of a film are determined in a diffuse interface model. A method is given, derived from a Fokker-Planck equation for the nonequilibrium particle distribution, which links atomic and mesoscopic events in a rheological description similar to the classical continuum theory of fluid flow. Film nucleation and growth are modeled by the spatially inhomogeneous continuous evolution of the instantaneous density profile which measures the average number of particles or molecules at given time and position.

Transport theory at the nanoscale. I. Surface waves.

Small scale particle motion is the cause of dynamic roughening and plays a role during film growth. To study surface waves on the molecular level, a continuum approach is used that links atomic and macroscopic dynamics though a Fokker-Planck equation for the distribution of particle trajectories. The dynamic equation for the density interfacial profile includes inertia terms indispensable for high frequency fluctuations.

Kinetic theory of gas separation in a nanopore and comparison to molecular dynamics simulation.

Kinetic mesoscopic theory derived from an atomistic model is applied to study permeation and separation of gases in a single rectangular pore. The goal is to judge the analytical method against the results of molecular dynamics simulation and to demonstrate the ease and relevance of analytical theories to calculate density profiles, flux, permeance, and separation factors. The permeance is linked to the amount of gas adsorbed in the pore and the effect of the effective gas-wall interaction on adsorption is explored.

Dynamics of atoms in a condensing cluster.

The dynamics of single particles in a cluster on condensation from the supersaturated vapor phase is studied by a kinetic approach. An insight into the distinctive flow field in the vicinity of a cluster is obtained for initial and late stage evolution. Inside the core the single atoms diffuse freely and the initial velocity decays rapidly with time.

Order in semiflexible polymers at an interface.

In the present paper, the simultaneous effect on a polymer of orientation by a solid surface and strong repulsion at the interface with an incompatible liquid is studied. Semiflexible polymers resist deformations perpendicular to the monomer and have a tendency to align in a given direction in contact with a surface. When a second incompatible liquid is added, a sharp interface between the two liquids forms at a given distance from the substrate.