Creeping of Salt Solutions: Influence of Surfactants

Salt creeping, the growth of crystals from evaporating salt solutions beyond the solution boundary, is a very common and fascinating phenomenon. It has a significant impact in industrial processes involving high salt concentrations, for the sodification of agricultural soils and for the preservation of salt-contaminated buildings and artworks¹. In spite of its importance, salt creeping remains poorly understood and there are consequently hardly or no measures to control the phenomenon². We present new experiments using a custom-made setup, that allows to reproduce the creeping phenomenon in the laboratory and study the influence of environmental conditions and additives. We show that during evaporation of salt solutions, the creeping starts only when the contact angle reaches a well-defined critical value, allowing us to propose a mechanism for the creeping dynamics. In addition, a nucleation promoting surfactant promotes creeping whereas a nucleation inhibitor prevents it.

(1) Hird, R.; Bolton, M. D. Migration of Sodium Chloride in Dry Porous Materials. Proc. R. Soc. A Math. Phys. Eng. Sci. 2016, 472 (2186), 20150710.
(2) Van Enckevort, W. J. P.; Los, J. H. On the Creeping of Saturated Salt Solutions. Cryst. Growth Des. 2013, 13 (5), 1838–1848.