Spiral diffusion of self-assembled dimers of Janus spheres

Modulating drift dynamics of circle swimmers by periodic potentials

We propose a method to modulate the drifting motion of overdamped circle swimmers in steady fluid flows by means of static sinusoidal potentials. Using Langevin formalism, we study drift velocity as a function of potential strength and wavelength with and without diffusional motion. Drift velocity is essentially quantized without diffusion, but in the presence of noise, the displacement per cycle has a continuous range. As a function of dimensionless potential wave number, domains of damped oscillatory and plateau regimes are observed in the drift velocity diagram. At weak potential and fluid velocity less than powered velocity, there is also a regime where drift velocity exceeds the fluid velocity. Methods based on these results can be used to separate biological and artificial circle swimmers based on their dynamical properties.

Memory effects in spiral diffusion of rotary self-propellers

The coupling of deterministic rotary motion and stochastic orientational diffusion of a self-propeller leads to a spiral trajectory of the expected displacement. We extend our former analysis of spiral diffusion [Phys. Rev. E 94, 030601(R) (2016)10.1103/PhysRevE.94.030601] in the white-noise limit to a more realistic scenario of stochastic noise with Gaussian memory and orientational fluctuations driven by an Ornstein-Uhlenbeck process. A variety of dynamical regimes including crossovers from ballistic to diffusive to ballistic in the angular dynamics are determined by the inertial timescale, orientational diffusivity, and angular speed.

Hydrodynamics of polymers in an active bath

The conformational and dynamical properties of active polymers in solution are determined by the nature of the activity. Here, the behavior of polymers with self-propelled, active Brownian particle-type monomers differs qualitatively from that of polymers with monomers driven externally by colored-noise forces. We present simulation and theoretical results for polymers in solution in the presence of external active noise. In simulations, a semiflexible bead-spring chain is considered, in analytical calculations, a continuous linear wormlike chain. Activity is taken into account by independent monomer or site velocities, with orientations changing in a diffusive manner. In simulations, hydrodynamic interactions (HIs) are taken into account by the Rotne-Prager-Yamakawa tensor or by an implementation of the active polymer in the multiparticle-collision-dynamics approach for fluids. To arrive at an analytical solution, the preaveraged Oseen tensor is employed. The active process implies a dependence of the stationary-state properties on HIs via the polymer relaxation times. With increasing activity, HIs lead to an enhanced swelling of flexible polymers, and the conformational properties differ substantially from those of polymers with self-propelled monomers in the presence of HIs, or free-draining polymers. The polymer mean-square displacement is enhanced by HIs. Over a wide range of timescales, hydrodynamics leads to a subdiffusive regime of the site mean-square displacement for flexible active polymers, with an exponent of 5/7, larger than that of the Rouse (1/2) and Zimm (2/3) models of passive polymers.

Amphiphilic Dimers at Liquid-Liquid Interfaces: A Density Functional Approach

We apply density functional theory to study the structure of dimers at the interface between two partially miscible symmetric liquids. The dimers are built of two tangentially jointed spheres and do not solve the coexisting liquids. The interactions in the system are modeled using Lennard-Jones potentials with different interactions between segments of the dimers and the liquid components. We study how asymmetry of the interactions between dimers and molecules of the liquid, i.e., the degree of dimer amphiphilicity, influences the interfacial structure. Two unexpected phenomena have been found. First, for some systems, the liquid-liquid interface is able to accommodate only a finite amount of dimers. If the amount of added dimers is larger than a threshold value, a part or all of the dimers move to the interior one of the coexisting phase, forming an insoluble sheet inside it, or the initial interface splits into separate parts. The second is a peculiar behavior of the dependence of the interfacial width with an increase of the amount of added dimers. In this case, we observe a discontinuous jump that is connected with reorientation of dimers with respect to the interface.

Density functional approach to the description of the structure of dimer nanoparticles at liquid–liquid interfaces

A density functional approach to the description of the structure of dimer nanoparticles at liquid–liquid interfaces.