(78f) Rheology of oil-water-surfactant interfaces measured from mesoscopic simulations

Understanding the dynamics of interfaces is significant for problems involving immiscible fluids subject to stress or deformation. The response of an interface to a stress is challenging to predict especially in the presence of surface active molecules. The interface response to dilatation and shear deformations can be of elastic and dissipative nature, depending on the concentration of adsorbed molecules on the interface, on the solicitation frequency and on the interaction between molecules. In this work, we develop a numerical experiment that allows to measure the different moduli in a unique framework based on the Dissipative Particle Dynamics (DPD). Insoluble surfactants are considered on an oil-water interface. The DPD parameters are tuned to find the correct surface tension at equilibrium. Pure dilatation and shear oscillations are applied separately. This allows measuring intrinsic elastic and viscous moduli of the interface in response to dilatation and shear deformations. The proposed method is demonstrated on water-oil-surfactant interfaces, but it can be readily applied to computing rheological properties of other complex interfaces.