The dynamic properties of interfaces often play a crucial role in the macroscopic dynamics of multiphase soft condensed matter systems. These properties affect the dynamics of emulsions, of dispersions of vesicles, of biological fluids, of coatings, of free surface flows, of immiscible polymer blends, and of many other complex systems. The study of interfacial dynamic properties, surface rheology, is therefore a relevant discipline for many branches of physics, chemistry, engineering, and life sciences. In the past three to four decades a vast amount of literature has been produced dealing with the rheological properties of interfaces stabilized by low molecular weight surfactants, proteins, (bio)polymers, lipids, colloidal particles, and various mixtures of these surface active components. In this paper recent experiments are reviewed in the field of surface rheology, with particular emphasis on the models used to analyze surface rheological data. Most of the models currently used are straightforward generalizations of models developed for the analysis of rheological data of bulk phases. In general the limits on the validity of these generalizations are not discussed. Not much use is being made of recent advances in nonequilibrium thermodynamic formalisms for multiphase systems, to construct admissible models for the stress-deformation behavior of interfaces. These formalisms are ideally suited to construct thermodynamically admissible constitutive equations for rheological behavior that include the often relevant couplings to other fluxes in the interface (heat and mass), and couplings to the transfer of mass from the bulk phase to the interface. In this review recent advances in the application of classical irreversible thermodynamics, extended irreversible thermodynamics, rational thermodynamics, extended rational thermodynamics, and the general equation for the nonequilibrium reversible-irreversible coupling formalism to multiphase systems are also discussed, and shown how these formalisms can be used to generate a wide range of thermodynamically admissible constitutive models for the surface stress tensor. Some of the generalizations currently in use are shown to have only limited validity. The aim of this review is to stimulate new developments in the fields of experimental surface rheology and constitutive modeling of multiphase systems using nonequilibrium thermodynamic formalisms and to promote a closer integration of these disciplines.

Dynamic properties of interfaces in soft matter: Experiments and theory

The time lag before establishment of a kinetic steady state is calculated for a linear multistate process in which there are only nearest‐neighbor transitions. This time is discussed with regard to general nonequilibrium behavior and the effect of this time lag in the rapid nucleation of a condensed phase in a gas is explored.

Time Lag in Multistate Kinetics: Nucleation

Slow quasistatic deformations of a fluid interface or membrane are investigated theoretically from a micromechanical viewpoint. The surface rate-of-strain tensor is characterized by its invariants, a and/3, which account for the interfacial dilation and shear, respectively. The macroscopic interfacial stretching and shearing tensions and the bending and torsion moments are expressed through integrals over the components of the pressure tensor. The results are applied to derive the Gibbsian fundamental thermodynamic equations of an arbitrarily curved interface from the fundamental equations of the adjacent bulk phases. Then, by means of a variational principle, the conditions for interfacial mechanical equilibrium are derived. © 1990 Academic Press, Inc.

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Frank P. Buff

Papers

The molecular hydrostatic analysis of Gibbs' theory of capillarity