Nick Quirke, Professor of Physical Chemistry and Head of the Computational, Theoretical and Structural Chemistry group at Imperial College, University of London, will present the following seminar from the Pacific Rim Conference in Nanoscience (7-11 September 2004). The seminar will be available for viewing and discussion through the Nanotech Hub at http://nanotech.colayer.net/:
The way fluids flow into and fill regular nanopores is of wide interest, however there are currently no experimental data or validated theoretical models for this nanoscale process. Nanoscale flow is dominated by surface properties and these can be studied using molecular simulation.
We first consider equilibrium and steady state flow in nanopores  and show using molecular dynamics that the tracer diffusivity depends only weakly on the conditions at the fluid–solid interface, whereas the collective diffusivity is a strong function of the hydrodynamic boundary conditions. A relationship between the collective diffusivity and the Maxwell coefficient describing wall collisions is obtained . The Maxwell coefficient is related to the surface friction and interfacial viscosity.
Turning to transient flows we have carried out molecular dynamics simulations of carbon nanotubes imbibing oil at an oil/vapour interface at 300K [3,4]. We find that the smallest (7,7) nanotubes imbibe extremely rapidly ( < or = 800 m/ s) along the inner tube surface with the penetration length L a linear function of time. We derive expressions for the penetration length L and the velocity of the imbibing oil and relate both to the solid-fluid surface tensions and interfacial friction via the Maxwell coefficient. The imbibition of oil by nanotubes is contrasted with the wetting of their external surfaces and that of planar surfaces. Density profiles (and the molecular structure) of the imbibing fluid in the pores are analysed as a function of time. We present  analytical expressions for the density profiles (in x and t) of the imbibing fluid as a function of the minimum decane-pore potential and the pore surface friction. We are therefore able to provide a complete description of imbibition of decane for a wide range of nanopores.
Finally we discuss nanopore- surface junctions and present molecular dynamics results for flow in such systems
1. V. P. Sokhan, D Nicholson and N Quirke, J Chem Phys, 117 ,8531, (2002)
2. V. P. Sokhan and N Quirke, Mol Sim, 30 , 217 (2004),
3. S Supple and N Quirke, Phys Rev Letts, 14501, 90 (2003)
4. S Supple and N Quirke, J Chem Phys (in press)
5. S Supple and N Quirke, J Chem Phys (submitted)
6. S Supple, PhD Thesis, Imperial College (submitted)