Water viscosity in confined nanoporous media and flow through nanofiltration membranes

• Published in: Microporous and mesoporous materials 2020-08, Vol.303, p.110289, Article 110289
• Main Authors: Álvarez-Quintana, Sara, Carmona, Francisco Javier, Palacio, Laura, Hernández, Antonio, Prádanos, Pedro
• Format: Article
• Language: English
• Subjects: Ceramic membranes; Nanoconfined water; Nanofiltration; Water adsorption energy; Water viscosity
• ISSN: 1387-1811; 1873-3093
• DOI: 10.1016/j.micromeso.2020.110289

Nanofiltration flux and selectivity depend on the mass transfer through the nanometric pores. Among other factors, including charges and dielectric constant for the charged species, viscosity is of crucial relevance. Here we study how viscosity changes in confined media in the nanometric range. The models found in the literature, that assume that the ratio of the viscosity of water on the pore walls over that in bulk water is a constant, are totally unsatisfactory to predict the dependence of the Darcy constant on temperature. Pure water flux is studied as a function of temperature for three commercial ceramic membranes. For these membranes, we fit flow versus temperature with a quite good fitting assuming that the first layer of water on the cylindrical pore walls move with a viscosity ηp=η0Ae−EaRT. If the flow is assumed to follow a Carman-Kozeny equation, according to its more realistic granular nature, the resulting porosity and mean grain size are in accordance with the data known and measured by atomic force microscopy (AFM). [Display omitted] •Water permeability through ceramic nanofiltration membranes is studied.•A model for water viscosity inside nanopores is proposed.•The changes in viscosity with temperature are studied.•The Carman-Kozeny model and our water viscosity model agree with the membrane granular morphology.