Microscopic fundamentals of the macroscopic interface formation principles

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To predict fluid motion, one needs to specify conditions at the domain boundaries, in particularly when a fluid meets a solid surface. For more than one hundred years, the standard no-slip boundary condition from the textbooks on continuum mechanics, which states that a fluid at a solid substrate has no relative velocity to it, has described much of our everyday experience. However, recent experiments have demonstrated that there is no strong argument to justify the no-slip condition and actually partial slip occurs. The reason for such behaviour turned out to be a thin liquid (interfacial) layer separating liquid and solid phases. The properties of this interfacial layer define the phenomenon of liquid slip and the effects of capillarity, that is, the effects related to the surface tension, and, in general, the nature of boundary conditions for the bulk flow. The interfacial layer becomes important when the system length scale shrinks to the microscale and the physical behaviour is largely influenced by high surface to volume ratio, which is the case for microfluidic flow conditions. So, it has been understood that in order to formulate correct boundary conditions for fluid flows at the microscale, it is necessary to describe rigorously the dynamics of the surface phase in the interfacial layer, interrelations of the surface phase flow with the bulk flow and the processes of interface formation. To summarise, generally one needs to describe capillary flows with forming interfaces.The capillary flows with forming interfaces are at the heart of numerous natural processes and technological applications ranging from coating devices, polymer films and new tools used in emerging technologies, such as micro and nano-fluidics, to biological and medical applications of fluid dynamics. Yet our understanding of fundamental principles of the interface formation is essentially incomplete. The main difficulty in quantitative description of these interfacial layers stems from the fact that they are physical systems with essentially mesoscopic structure which has strong anisotropy involving both macroscopic and molecular scales as well as forces of differing nature.The objective of this interdisciplinary project is to study fundamentals of the interface formation by bridging two major developments in interfacial science, the microscopic approach based on molecular dynamics simulations and the macroscopic theory of interface formation based on the methods of irreversible thermodynamics. Only recently the two approaches have become mature and powerful enough to rigorously address dynamical aspects of the surface phase and formation of interfaces and the time is ripe to perform such fundamental studies from the first microscopic principles.We are going to search for the foundation of macroscopic theories by means of microscopic molecular dynamics studies. This will allow to test and to improve the existing macroscopic theories and to develop new methodologies. The outcome of this proposal can be widely exploited in different research communities to quantitatively model capillary flows with forming interfaces.