Speaker
Description
Capillarity-driven flows in pores a few nanometers in diameter play an important role in many natural and technological processes, for example in clay swelling, frost heave, catalysis and transport across artificial nanostructures, bio-membranes and tissues [1]. Here we present molecular dynamics simulations modelling the capillary flow of water into silica nano-pores (MCM-41) of around 3 nm diameter pore size. By the usage of water-water [2], water-silica [3] and silica-silica [4] forcefield implementations we are able to simulate the spontaneous imbibition dynamics of water into the silica pores. The simulations confirm that the dynamics of the penetration depth of the fluid $L$ into cylindrical pores after time $t$ can be described by the Lucas-Washburn equation, $L = \sqrt{v_i} \sqrt{t}$. $v_i$ is the so-called "imbibition speed" that depends on the ratio of the fluid parameters, the fluid/wall interaction, the radius of the pores and the hydrodynamic slip-boundary condition [5]. Further, the capillary flow induced strain in the host material resulting from the surface stress release (Bangham effect) and the acting Laplace pressures are investigated on a nanoscopic scale [6]. Of particular interest is the observed anisotropy in magnitude of strain in lateral and longitudinal pore direction which lacks theoretical description yet. Therefore, the simulations contribute valuable insights to the understanding of imbibition induced strains in materials. In combination with small angle and wide angle X-ray scattering (SAXS/WAXS) measurements of imbibition induced strain the simulation will lead to an overall better understanding of capillary-driven flows and its effects on the the host material [7].
[1] Huber, P. Journal of Physics Condensed Matter 2015, 27, 43, DOI: 10.1088/0953-8984/27/10/103102.
[2] Abascal, J. L.; Vega, C. The Journal of Chemical Physics 2005, 123, 234505, DOI: 10.1063/1.2121687.
[3] Cole, D. J.; Payne, M. C.; Csányi, G.; Spearing, S. M.; Ciacchi, L. C. Journal of Chemical Physics 2007, 127, 204704, DOI: 10.1063/1.2799196.
[4] Meißner, R. H.; Schneider, J.; Schiffels, P.; Colombi Ciacchi, L. Langmuir 2014, 30, 3487–3494, DOI: 10.1021/la500285m.
[5] Gruener, S.; Hofmann, T.; Wallacher, D.; Kityk, A. V.; Huber, P. Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 2009, 79, 067301, DOI: 10.1103/PhysRevE.79.067301.
[6] Gor, G. Y.; Huber, P.; Weissmüller, J. Physical Review Materials 2018, 2, 086002, DOI: 10.1103/PhysRevMaterials.2.086002.
[7] Prass, J.; Müter, D.; Fratzl, P.; Paris, O. Applied Physics Letters 2009, 95, 083121, DOI: 10.1063/1.3213564.
