Exact solutions for viscous Marangoni spreading.

When surface-active molecules are released at a liquid interface, their spreading dynamics is controlled by Marangoni flows. Though such Marangoni spreading was investigated in different limits, exact solutions remain very few. Here we consider the spreading of an insoluble surfactant along the interface of a deep fluid layer.

Spreading dynamics of reactive surfactants driven by Marangoni convection.

We consider the spreading dynamics of some insoluble surface-active species along an aqueous interface. The model includes both diffusion, Marangoni convection and first-order reaction kinetics. An exact solution of the nonlinear transport equations is derived in the regime of large Schmidt number, where viscous effects are dominant.

Erratum: Polarization of active Janus particles [Phys. Rev. E 89, 050303(R) (2014)].

This corrects the article DOI: 10.1103/PhysRevE.89.

Light-Driven Transport of a Liquid Marble with and against Surface Flows.

Liquid marbles, that is, liquid drops coated by a hydrophobic powder, do not wet any solid or liquid substrate, making their transport and manipulation both highly desirable and challenging. Herein, we describe the light-driven transport of floating liquid marbles and emphasize a surprising motion behavior. Liquid marbles are deposited on a water solution containing photosensitive surfactants.

Polarization of active Janus particles.

We theoretically study the motion of surface-active Janus particles, driven by an effective slip velocity due to a nonuniform temperature or concentration field ψ. With parameters realized in thermal traps, we find that the torque exerted by the gradient ∇ψ inhibits rotational diffusion and favors alignment of the particle axes. In a swarm of active particles, this polarization adds a novel term to the drift velocity and modifies the collective behavior.

Flow pattern in the vicinity of self-propelling hot Janus particles.

We study the temperature field and the resulting flow pattern in the vicinity of a heated metal-capped Janus particle. If its thickness exceeds about 10 nm, the cap forms an isotherm and the flow pattern comprises a quadrupolar term that decays with the square of the inverse distance ~r(-2). For much thinner caps the velocity varies as ~r(-3).

Nonequilibrium fluctuations of an interface under shear.

The steady-state properties of an interface in a stationary Couette flow are addressed within the framework of fluctuating hydrodynamics. Our study reveals that thermal fluctuations are driven out of equilibrium by an effective shear rate that differs from the applied one. In agreement with experiments, we find that the mean-square displacement of the interface is reduced by the flow.

Cryo-electron tomography of nanoparticle transmigration into liposome.

Nanoparticle transport across cell membrane plays a crucial role in the development of drug delivery systems as well as in the toxicity response induced by nanoparticles. As hydrophilic nanoparticles interact with lipid membranes and are able to induce membrane perturbations, hypothetic mechanisms based on membrane curvature or hole formation have been proposed for activating their transmigration. We report on the transport of hydrophilic silica nanoparticles into large unilamellar neutral DOPC liposomes via an internalization process.

Thermophoresis of charged colloidal particles.

Thermally induced particle flow in a charged colloidal suspension is studied in a fluid-mechanical approach. The force density acting on the charged boundary layer is derived in detail. From Stokes' equation with no-slip boundary conditions at the particle surface, we obtain the particle drift velocity and the thermophoretic transport coefficients.

Hindered mobility of a particle near a soft interface.

The translational motion of a solid sphere near a deformable fluid interface is studied in the low Reynolds number regime. In this problem, the fluid flow driven by the sphere is dynamically coupled to the instantaneous conformation of the interface. Using a two-dimensional Fourier transform technique, we are able to account for the multiple backflows scattered from the interface.

Thermodiffusion of charged micelles.

We study diffusion of charged nanoparticles in a temperature gradient and derive the corresponding Ludwig-Soret transport coefficient. Charge effects are found to enhance thermodiffusion by up to 2 orders of magnitude. We show that the inverse Soret coefficient 1/S(T) is a linear function of the colloid density n; the proportionality factor, or second virial coefficient, varies algebraically with inverse salinity, n0(-alpha); the precise value of the exponent alpha depends on the ratio of particle size and Debye length.

The nuclear pore complex mystery and anomalous diffusion in reversible gels.

The exchange of macromolecules between the cytoplasm and the nucleus of eukaryotic cells takes place through the nuclear pore complex (NPC), which contains a selective permeability barrier. Experiments on the physical properties of this barrier appear to be in conflict with current physical understanding of the rheology of reversible gels. This paper proposes that the NPC gel is anomalous and characterized by connectivity fluctuations.