Controlling the composition of a confined fluid by an electric field

Dynamics of field-driven population inversion in a confined colloidal mixture

We study, using Langevin dynamics simulations, the change in composition of a binary colloidal mixture confined in a finite-length channel, induced by an external field. The field-induced transition from a near-bulk composition to an inverted population is studied as a function of time, for different field strengths and system parameters. For state points corresponding to reversible field cycles, the cyclic filling and emptying of the channel by the minority species are compared. Extrapolation of the physical relaxation times to the colloidal regime is performed through a series of simulations at increasing value of the damping parameter. For state points at which the mixture is unstable at zero field, reproducible irreversible cycles are illustrated. For reversible field cycles, the scaling with the particles size of the characteristic cycling time is discussed.

Vapor-liquid coexistence of the Stockmayer fluid in nonuniform external fields

We investigate the structure and phase behavior of the Stockmayer fluid in the presence of nonuniform electric fields using molecular simulation. We find that an initially homogeneous vapor phase undergoes a local phase separation in a nonuniform field due to the combined effect of the field gradient and the fluid vapor-liquid equilibrium. This results in a high-density fluid condensing in the strong field region. The system polarization exhibits a strong field dependence due to the fluid condensation.

Nonadditive penetrable mixtures in nanopores: surface-induced population inversion

We investigate the surface-induced population inversion of the nonadditive penetrable mixtures which exhibits the fluid-fluid demixing transition of the bulk system due to the confinement effect. The result shows that the population inversions are strongly affected by the extra repulsion between unlike species, the mole fraction of species, the width of nanopores, and the nonadditive walls. The extra repulsion between unlike species in a confined system increases the contact density of both species at the wall and promotes the population inversion in nanopores. The population inversion is the typical shift first-order fluid-fluid demixing transition due to the confinement effect in nanopores. The population inversions are only observed in nanopores with finite widths. The population inversion line is shifted toward a higher fluid density with decreasing width of the nanopores and lies slightly in lower density compared with the coexistence curves of the bulk system. The nonadditive wall for the big particles leads to the population inversion in lower density compared with that of the nonadditive wall for the small particles. The population inversion line is terminated at a lower mole fraction.

Binary mixture adsorbed in a slit pore: Field-induced population inversion near the bulk instability

The recently proposed method for modulating through an external field the composition of a binary fluid mixture adsorbed in a slit pore is discussed. The population inversion near the bulk (demixing) instability is first analyzed in the case of a symmetric mixture of nonadditive hard spheres, without field. It is next investigated for a mixture comprising dipolar particles subject to an external field. The influence of several factors on the adsorption curves including bulk composition, pore width, field direction, polarizability versus permanent dipoles, and temperature on this field induced population inversion is shown by Monte Carlo simulation.