Dr Ahmad Jabbarzadeh
Telephone: 93512346, email: ahmadj@mech.eng.usyd.edu.au
Molecular Dynamics Simulation of Polymeric Fluids in Thin Film Lubrication
Objective:
Understanding properties of thin liquid films in confined geometry is very important in many applications such as lubrication, coating and polymer processing. At extreme conditions of high shear rates and temperature in ultra-thin films measuring the rheological properties and studying the behavior of the film is very difficult with experimental techniques. Molecular dynamics simulation are used in our studies to investigate the behavior of these thin films that exhibit deviation from continuum mechanics. This is mainly because of inhomogeneity that is a result of wall effect. These thin films show enhanced viscosity and shear thinning effects, We have studied many properties of the confined film, the effect of the wall properties on its behavior, boundary conditions, slip, rheological properties and structural effects.
Background:
Molecular dynamics simulations are used as a first principle method to study physical phenomena. This method is specially useful where there is no existing model for the problem under investigation or the existing models do not work. In principle using Newton's second law and integrating the equations of motion, positions and velocities of the atoms are calculated. Then statistical mechanics principles are used to calculate tome average macroscopic properties such as, temperature, pressure, stress tensor, viscosity, etc of the material. The beauty of molecular dynamics is that you need only few hundred or few thousand atoms to examine the properties of the matter. This means a sample only few nano-meter on each side.
In rheology group we have put emphasis on the rheological properties of confined films and complex flows through narrow channels. We use a complex and realistic model to simulate molecules such as, tetracosane, squalane, short polyethylene molecules and linear and branched molecules (example) . Some of the research work in this area are shown below:
- Model lubricant consisted of branched molecules of 2,3,6,7,10,11,hexapropyldodecane is confined between to solid walls and undergone shear flow at shear rate of 1011 1/s. The film thickness in 7.2 nm. See AVI format (17 MB)
- Simulation of Poiseuille flow throgh a narrow channel and over a sharp corner. Molecules are Hexadecane (C16H34) molecules. See AVI format (10 MB)
- Simulation of C100H202 molecules near the wall asperities. See the Animated GIF format file (6.6 MB) or AVI format (10 MB)
- A single molecule of 2,3,6,7,10,11,hexapropyldodecane is shown in Couette shear flow simulation of these branched molecules. See the Animated GIF format (105 KB) or the AVI format (1.04 MB)
- A single molecule Squalane is shown in Couette shear flow simulation of these branched molecules. See the Animated GIF format (110 KB)or the AVI format (1.1 MB)
- A single molecule tetracosane is shown in Couette shear flow simulation of these linear molecules. See the Animated GIF format (110 KB) or the AVI format (1.1 MB).
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