TYC Soiree: New understanding of liquids and supercritical fluids
Date: 3 December 2015 Time: 17:00 - 19:00
New understanding of liquids and supercritical fluids: their flow, statistical-mechanical, dynamical and thermodynamic properties
A never ending journey. Singularities, Slip, Substrates and Structure: Challenges of modelling the moving contact line problem.
Serafim Kalliadasis, Department of Chemical Engineering, Imperial College
The moving contact line problem occurs when modelling one fluid replacing another as it moves along a solid surface, a situation widespread throughout industry and nature. Classically, the no-slip boundary condition at the solid substrate, a zero-thickness interface between the fluids, and motion at the three-phase contact line are incompatible - leading to the well-known shear-stress singularity. In this talk we will review recent progress made by our group, considering the problem and related physics from the micro to macroscopic length scales. This includes comparing a variety of models used to overcome the singularities, based on slip, disjoining pressure, interface formation and diffuse-interfaces; analysing the impact of random substrate heterogeneities and inclinations; and exploring the detailed nature of the fluid structure in the vicinity of the contact line at the smallest scales by developing rigorously justified models based on the statistical mechanics of fluids.
Between glass and gas: Liquids at supercritical pressures
Vadim Brazhkin, Institute for High Pressure Physics, Russian Academy of Sciences, Russia
A liquid near the melting curve has much more in common with a solid than with a gas – this interesting result has been increasingly appreciated recently in the area of liquids, although not widely by physics community in general. For example, a liquid supports transverse collective modes at high frequency that endow the liquid with shear rigidity at that frequency. Many physical properties, including heat capacity, heat conductivity, electronic conductivity and so on, change only weakly as a result of melting despite the loss of the long-range order. Close to the melting curve, this behavior is observed at very high pressures and temperatures well above the critical point. To denote this state of the liquid, the term “rigid liquid” was proposed. In a rigid liquid, particle motion consists of fairly rare jumps over the activation barrier and oscillatory motion in between the jumps. This is reflected in relaxation time ?, the time between two consecutive particle jumps, being larger than the shortest vibration period ?0 (?0=2?/?0, where ?0 is the maximal frequency of transverse-like modes). Recently, we have shown that the condition ? ? ?0defines a line, the “Frenkel line” on the pressure-temperature (or density-temperature) phase diagram that separates the state of the rigid-liquid from the dense gas. Crossing the Frenkel line on temperature increase results in the disappearance of shear rigidity at all frequencies, specific heat reaching 2kB, and, importantly, the qualitative change of temperature dependence of key system properties such as structure factor features, heat capacity, speed of sound, diffusion coefficient, viscosity and thermal conductivity.
Here we present new results of liquid-to-dense gas transition at very high pressures for real fluids such as iron, water, CO2, CH4. The interconnections of the Frenkel line with the metal-semiconductor transition and different version of percolation lines will be also considered. The data of the location of the lines of liquid-to-dense gas transition at supercritical pressures are very important for supercritical technologies.
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