Modelling the rheology of anisotropic particles adsorbed on a two-dimensional fluid interface
Luo, A.M. ; Sagis, L.M.C. ; Oettinger, H.C. ; Michele, C. de; Ilg, P. - \ 2015
Soft Matter 11 (2015). - ISSN 1744-683X - p. 4383 - 4395.
complex fluids - capillary interactions - constitutive equation - general formalism - liquid-crystals - dynamics - thermodynamics - emulsions
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.
Nonequilibrium thermodynamics of nucleation
Schweizer, M. ; Sagis, L.M.C. - \ 2014
Journal of Chemical Physics 141 (2014). - ISSN 0021-9606 - 13 p.
homogeneous nucleation - inhomogeneous-media - general formalism - complex fluids - systems - clusters - dynamics - temperature - interface - equations
We present a novel approach to nucleation processes based on the GENERIC framework (general equation for the nonequilibrium reversible-irreversible coupling). Solely based on the GENERIC structure of time-evolution equations and thermodynamic consistency arguments of exchange processes between a metastable phase and a nucleating phase, we derive the fundamental dynamics for this phenomenon, based on continuous Fokker-Planck equations. We are readily able to treat non-isothermal nucleation even when the nucleating cores cannot be attributed intensive thermodynamic properties. In addition, we capture the dynamics of the time-dependent metastable phase being continuously expelled from the nucleating phase, and keep rigorous track of the volume corrections to the dynamics. Within our framework the definition of a thermodynamic nuclei temperature is manifest. For the special case of nucleation of a gas phase towards its vapor-liquid coexistence, we illustrate that our approach is capable of reproducing recent literature results obtained by more microscopic considerations for the suppression of the nucleation rate due to nonisothermal effects.
Dynamics of multiphase systems with complex microstructure. I. Development of the governing equations through nonequilibrium thermodynamics
Sagis, L.M.C. ; Öttinger, H.C. - \ 2013
Physical Review. E, Statistical nonlinear, and soft matter physics 88 (2013)2. - ISSN 1539-3755 - 13 p.
scanning angle reflectometry - in-water emulsions - superficial viscosity - general formalism - bending rigidity - lipid-bilayers - interfaces - surface - fluid - rheology
In this paper we present a general model for the dynamic behavior of multiphase systems in which the bulk phases and interfaces have a complex microstructure (for example, immiscible polymer blends with added compatibilizers, or polymer stabilized emulsions with thickening agents dispersed in the continuous phase). The model is developed in the context of the GENERIC framework (general equation for the nonequilibrium reversible irreversible coupling). We incorporate scalar and tensorial structural variables in the set of independent bulk and surface excess variables, and these structural variables allow us to link the highly nonlinear rheological response typically observed in complex multiphase systems, directly to the time evolution of the microstructure of the bulk phases and phase interfaces. We present a general form of the Poisson and dissipative brackets for the chosen set of bulk and surface excess variables, and show that to satisfy the entropy degeneracy property, we need to add several contributions to the moving interface normal transfer term, involving the tensorial bulk and interfacial structural variables. We present the full set of balance equations, constitutive equations, and boundary conditions for the calculation of the time evolution of the bulk and interfacial variables, and this general set of equations can be used to develop specific models for a wide range of complex multiphase systems.
Normal stresses in surface shear experiments
Sagis, L.M.C. - \ 2013
The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 99 - 103.
in-water emulsions - interfacial permeability - general formalism - bending rigidity - complex fluids - dynamics - viscoelasticity - thermodynamics - liquid/liquid - gas/liquid
When viscoelastic bulk phases are sheared, the deformation of the sample induces not only shear stresses, but also normal stresses. This is a well known and well understood effect, that leads to phenomena such as rod climbing, when such phases are stirred with an overhead stirrer, or to die swell in extrusion. Viscoelastic interfaces share many commonalities with viscoelastic bulk phases, with respect to their response to deformations. There is however little experimental evidence that shear deformations of interfaces can induce in-plane normal stresses (not to be confused with stresses normal to the interface). Theoretical models for the stress-deformation behavior of complex fluid-fluid interfaces subjected to shear, predict the existence of in-plane normal stresses. In this paper we suggest methods to confirm the existence of such stresses experimentally.
Modeling interfacial dynamics using nonequilibrium thermodynamics frameworks
Sagis, L.M.C. - \ 2013
The European Physical Journal. Special Topics 222 (2013)1. - ISSN 1951-6355 - p. 105 - 127.
extended irreversible thermodynamics - scanning angle reflectometry - in-water emulsions - adsorption layers - surface rheology - 2-dimensional suspensions - superficial viscosity - reciprocal relations - general formalism - polymer-solutions
In recent years several nonequilibrium thermodynamic frameworks have been developed capable of describing the dynamics of multiphase systems with complex microstructured interfaces. In this paper we present an overview of these frameworks. We will discuss interfacial dynamics in the context of the classical irreversible thermodynamics, extended irreversible thermodynamics, extended rational thermodynamics, and GENERIC framework, and compare the advantages and disadvantages of these frameworks.
An extended rational thermodynamics model for surface excess fluxes
Sagis, L.M.C. - \ 2012
Physica A 391 (2012)4. - ISSN 0378-4371 - p. 979 - 990.
irreversible thermodynamics - general formalism - complex fluids - kinetic-theory - dynamics - fluctuations - interfaces - rheology - bilayers
In this paper, we derive constitutive equations for the surface excess fluxes in multiphase systems, in the context of an extended rational thermodynamics formalism. This formalism allows us to derive Maxwell–Cattaneo type constitutive laws for the surface extra stress tensor, the surface thermal energy flux vector, and the surface mass flux vector, which incorporate a direct coupling to their corresponding bulk fluxes in the adjacent bulk phases. These constitutive laws also incorporate contributions to the time evolution of the surface excess fluxes from spatial inhomogeneities in these flux fields. These phenomenological equations can be used to model the dynamic behavior of complex viscoelastic interfaces in multiphase systems, in the small deformation limit.
Rheology of interfaces stabilized by a 2D suspension of anisotropic particles: a classical irreversible thermodynamics theory
Sagis, L.M.C. - \ 2011
Soft Matter 7 (2011)17. - ISSN 1744-683X - p. 7727 - 7736.
nonequilibrium thermodynamics - superficial viscosity - general formalism - latex-particles - complex fluids - liquid - liquid/liquid - dynamics - viscoelasticity - gas/liquid
Surface rheological properties have a significant impact on the stability of particle-stabilized emulsions and foams. Interfaces stabilized by anisotropic particles display a highly nonlinear surface rheology, even at relatively small deformation rates. The nonlinearity of the response is the result of changes in the microstructure of the interface, induced by the applied deformation. The particles are oriented in the direction of the imposed flow field, and this leads to a decrease in the surface shear viscosity (shear thinning). In this paper we derive nonlinear constitutive equations for the surface stress tensor of an interface stabilized by a mixture of anisotropic particles and low molecular weight surfactants, using the classical irreversible thermodynamics formalism. These equations are valid in the low shear regime, where departures from linear behavior are still small. The effect of the microstructure of the interface on the rheological response is incorporated through the particle orientation tensor Qs. The constitutive equations are able to predict the shear thinning behavior observed experimentally for this type of interface.
Rheology of complex fluid-fluid interfaces: a unified approach based on nonequilibrium thermodynamics
Sagis, L.M.C. - \ 2010
Applied Rheology 20 (2010)2. - ISSN 1430-6395 - p. 24380 - 24380.
extended irreversible thermodynamics - general formalism - surface rheology - dynamics - microbubbles - deformation - equilibrium - equation - systems - layers
Surface rheological properties affect the dynamics of vesicles, nanoparticles, emulsion droplets, foam bubbles, polymer microcapsules, liquid jets, living cells, lung avioli, thin liquid films, and many other multiphase systems. Surface rheology is therefore relevant for a wide range of disciplines in the areas of physics, chemistry, engineering, biology, and medicine. Currently used descriptions of surface rheology have a number of limitations, and in particular are hard to generalize to the large deformation regime. Data are often analyzed with constitutive equations based on straightforward generalizations of models developed for describing bulk phase rheology. Since the latter are in general designed to describe incompressible materials, they are not guaranteed to describe highly compressible interfaces correctly. Here we discuss a unified approach to surface rheology based on nonequilibrium thermodynamics (NET) that provides a consistent set of balance and constitutive equations for the unambiguous determination of surface rheological parameters, both near and far beyond equilibrium. A closer integration of experimental surface rheology and multiphase nonequilibrium thermodynamics would clearly be beneficial for both disciplines