Ordering of amphiphilic Janus particles at planar walls: A density functional study

Abstract

We investigate the structure formation of amphiphilic molecules at planar walls using density functional theory. The molecules are modeled as (hard) spheres composed of a hydrophilic and hydrophobic part. The orientation of the resulting Janus-particles is described as a vector representing an internal degree of freedom. Our density functional approach involves Fundamental Measure Theory combined with a mean-field approximation for the anisotropic interaction. Considering neutral, hydrophilic and hydrophobic walls, we study the adsorption of the particles, focussing on the competition between the surface field and interaction-induced ordering phenomena. Finally, we consider systems confined between two planar walls. It is shown that the anisotropic Janus interaction yields pronounced frustration effects at low temperatures.

Micelle and Bilayer Formation of Amphiphilic Janus Particles in a Slit-Pore

“…In a study by Hirose et al ., a macroscopic approach (based on Young’s equation) was used to study the wetting properties of Janus systems [22], but not their self-assembly. More recently, we have proposed a density functional theory (DFT) approach [23], where detailed properties such as density and orientation profiles at the surface can be calculated on the basis of the microscopic Hamiltonian. Indeed, to describe the interaction between such particles on an effective level (that is, without taking explicitly into account the solvent), various models have been proposed [1,16,18,24].…”

“…Indeed, to describe the interaction between such particles on an effective level (that is, without taking explicitly into account the solvent), various models have been proposed [1,16,18,24]. In [23] we employed a model originally suggested by Tarazona et al . [18] to describe surfactant molecules on a highly coarse-grained level, that is, by representing the surfactant as a sphere.…”

“…The orientation of the resulting Janus particles is incorporated by a unit vector pointing from the hydrophobic to the hydrophilic side. While the model is appropriate for DFT calculations [23], a drawback is that it requires an ansatz for the symmetry of the density profile. In [23] we restricted ourselves to the investigation of planar structures formed at the planar surfaces.…”

“…While the model is appropriate for DFT calculations [23], a drawback is that it requires an ansatz for the symmetry of the density profile. In [23] we restricted ourselves to the investigation of planar structures formed at the planar surfaces. Indeed, it turned out that (neutral or hydrophilic) surfaces strongly stabilize the formation of bilayers consisting of two layers of oppositely oriented Janus particles.…”

How to model the interaction of charged Janus particles

“…Since then, they have been of large interest due to their anisotropic character, and today not only particles with hydrophilic-hydrophobic interaction [2,3] are synthetically accessible but also magnetic [4][5][6] or charged [7,8] particles. For a better understanding of the particle properties, e ort has been put into theoretical investigations: the self-assembly behaviour and phase diagrams of hard spheres [9][10][11] and soft spheres [12,13] have been studied, for example, as well as the structure formation on surfaces [14,15] and the interaction with surfaces [16] .…”