Modelling the rheology of anisotropic particles adsorbed on a two-dimensional fluid interface

Abstract

We present a general approach based on nonequilibrium thermodynamics for bridging the gap between a well-defined microscopic model and the macroscopic rheology of particle-stabilised interfaces. Our approach is illustrated by starting with a microscopic model of hard ellipsoids confined to a planar surface, which is intended to simply represent a particle-stabilised fluid-fluid interface. More complex microscopic models can be readily handled using the methods outlined in this paper. From the aforementioned microscopic starting point, we obtain the macroscopic, constitutive equations using a combination of systematic coarse-graining, computer experiments and Hamiltonian dynamics. Exemplary numerical solutions of the constitutive equations are given for a variety of experimentally relevant flow situations to explore the rheological behaviour of our model. In particular, we calculate the shear and dilatational moduli of the interface over a wide range of surface coverages, ranging from the dilute isotropic regime, to the concentrated nematic regime.

Self-assembly of ellipsoidal particles at fluid-fluid interfaces with an empirical pair potential

“…Having established an approximate pair potential that extends Eq. (4) to include these other relevant interactions allows a more thorough investigation into the 410 structure formation, phase behavior and dynamical properties along the lines explored in Luo et al [67]. In addition, we could extend our modelling procedure to allow for ellipsoids that tilt out of the interface, which has been experimentally observed by compressing a surface monolayer [68] and computationally modelled with magnetic particles in a magnetic field [69,70].…”

Dynamic heterogeneity in complex interfaces of soft interface-dominated materials

“…Such models can be created either in the 2d Gibbs dividing surface, or 3d diffuse interface framework 12 . In the former this can be done by starting from a detailed microscopic model that is subsequently coarse-grained to a 2d model 40 , describing in-plane dynamics, and transfer processes between bulk and interface. Both approaches require a fundamental change in how complex interfaces are currently being viewed.…”

Surface Rheology and Structure of Model Triblock Copolymers at a Liquid–Vapor Interface: A Molecular Dynamics Study

“…The latter is also of major importance in the interpretation of experimental data obtained from interfacial shear rheology experiments. 39,40 There have been a couple of Brownian dynamics simulation 41−43 and theoretical 44 studies on the structure and rheology of particle-stabilized interfaces in which the bulk phases carrying the interface were treated implicitly via a steep potential well or not considered at all. While these studies provided physical insights into the surface structure− rheology relationship and allowed making use of classical NEMD algorithms based on homogeneous deformation of the entire simulation box, 45 they neglected (i) the presence of bulk phases that can dramatically alter the interfacial microstructure 46 and (ii) the contribution of momentum transfer between the bulk and interface to the surface stress relaxation, which has recently been shown to be of crucial importance in interfacial dynamics.…”

“…Computer simulations of interfacial films were mostly limited to low-molecular-weight surfactants and focused mainly on their equilibrium properties such as surface pressure–area isotherms and equilibrium microstructures. ,, Apart from difficulties in setting up simulations of such heterogeneous systems, applying in-plane affine deformation and decomposing the resulting stress signal into surface and bulk contributions are additional technical difficulties present in simulations of these interfacial systems. The latter is also of major importance in the interpretation of experimental data obtained from interfacial shear rheology experiments. , There have been a couple of Brownian dynamics simulation − and theoretical studies on the structure and rheology of particle-stabilized interfaces in which the bulk phases carrying the interface were treated implicitly via a steep potential well or not considered at all. While these studies provided physical insights into the surface structure–rheology relationship and allowed making use of classical NEMD algorithms based on homogeneous deformation of the entire simulation box, they neglected (i) the presence of bulk phases that can dramatically alter the interfacial microstructure and (ii) the contribution of momentum transfer between the bulk and interface to the surface stress relaxation, which has recently been shown to be of crucial importance in interfacial dynamics …”