Keith E. Gubbins学术报告
来源：浙江大学化学系
发布时间：2011-11-01
8193
报告题目：High Pressure Effect and Material Deformation due to Confined Nanophases
报告人：Keith E. Gubbins
Member of National academy of engineering W.H.Clark Distinguished
University Professor
Director, Institute for Computational Science &Engineering
North Carolina State University U.S.A.
时间：11月3日（星期四）上午·9:30
地点： 教八218
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Abstract
There is an abundance of anecdotal evidence that nanophases adsorbed within nanoporous materials exhibit high pressures as a result of the confinement. For example, phase changes and chemical reactions that only occur at high pressures in the bulk phase occur in the confined phase at bulk phase pressures that are orders of magnitude lower.1 The structure of confined ice has been studied in carbon nanotubes using molecular simulation2 and experiment,3 and provides convincing evidence for the formation of different kinds of ice nanocrystals, including ice VII and ice IX, phases that only occur at pressures of GPa and above in bulk water. Examples of chemical reactions that occur at low bulk pressures in nano-pores, but only at very high pressures in the bulk phase, have also been frequently observed in experiments4 and molecular simulations5.
We report a study6,7, using semi-grand canonical Monte Carlo and molecular dynamics simulations, of the pressure tensor in nano-pores of simple slit-shaped and cylindrical geometries. We show that for nano-scale pores (pore widths from 0 to 8 molecular diameters) the tangential pressure can be locally very high, tens of thousands of bars, in the pore, even though the bulk phase in equilibrium with the pore is at pressures of one bar or less. Moreover, the in-pore tangential pressure is very sensitive to small changes in the pressure of the bulk phase in equilibrium with the pore phase, indicating a way to experimentally control the in-pore pressure. These very high in-pore pressures result from the strong interaction with the pore walls, which results in compression of the molecules in the confined nanophase, leading to strong repulsive intermolecular forces in the tangential direction. This gives rise to large and positive tangential pressures. The pressure normal to the pore walls is also large, and oscillates between positive and negative values, depending on the pore width. The normal pressure (approximately equal to the solvation pressure) causes changes to the pore width and interlayer spacing on adsorption. Such changes have been observed in recent x-ray and neutron diffraction experiments. We report such changes for nanoporous carbons, silicas and micas, and make qualitative comparisons with experimental results.
1. Gelb, L. D.; Gubbins, K. E.; Radhakrishnan, R.; Sliwinska-Bartkowiak, M. Rep. Progr. Phys., 1999,
62, 1573.
2. Takaiwa, D.;Hatano, I.; Koga, K.; Tanaka, H. Proc. Natl. Acad. Sci. U. S. A., 2008, 105, 39.
3. Matsuda, K.; Hibi,T.; Kadowaki, H.; Katara, H.; Maniwa, Y.Phys.Rev.B, 2006 ,74, 073415.
4. e.g. K. Kaneko, N. Fukuzaki, K. Kakei, T. Suzuki and S. Ozeki, Langmuir, 5, 960 (1989); Byl, O.;
Kondratyuk, P.; Yates, J.T., Jr., J. Phys. Chem. B, 2003, 107, 4277.
5. e.g. Turner, C.H.; Johnson, J.K.; Gubbins, K.E., J. Chem. Phys., 2001, 114, 1851.
6. Yun Long, Jeremy C. Palmer, Benoit Coasne, Małgorzata Śliwinska-Bartkowiak and Keith E. Gubbins,
“Pressure enhancement in carbon nanopores: A major confinement effect”, Physical Chemistry Chemical
Physics, 13, 17163-17170 (2011).
7. Yun Long, Jeremy C. Palmer, Benoit Coasne, Malgorzata Śliwinska-Bartkowiak and Keith E. Gubbins,
“Under Pressure: Quasi-High Pressure Effects in Nanopores”, Microporous and Mesoporous Materials,
DOI: 10.1016/j.micromeso.2011.07.017 (2011).