Wetting dynamics of nanoliter water droplets in nanoporous media

Bin Pan; Christopher R Clarkson; Marwa Atwa; Chris Debuhr; Amin Ghanizadeh; Viola I Birss

doi:10.1016/j.jcis.2020.12.108

Wetting dynamics of nanoliter water droplets in nanoporous media

J Colloid Interface Sci. 2021 May:589:411-423. doi: 10.1016/j.jcis.2020.12.108. Epub 2020 Dec 31.

Authors

Bin Pan¹, Christopher R Clarkson², Marwa Atwa³, Chris Debuhr², Amin Ghanizadeh², Viola I Birss⁴

Affiliations

¹ Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB T2N 1N4, Canada.
² Department of Geoscience, University of Calgary, Calgary, AB T2N 1N4, Canada.
³ Department of Chemistry, University of Calgary, Calgary, AB T2N 1N4, Canada; Department of Chemistry, Suez Canal University, El Salam District, Ismailia 41522, Egypt.
⁴ Department of Chemistry, University of Calgary, Calgary, AB T2N 1N4, Canada.

PMID: 33485249
DOI: 10.1016/j.jcis.2020.12.108

Abstract

Hypothesis: The Lucas-Washburn (L-W) equation is the classical theory to describe the dynamics of spontaneous imbibition in single micro-channels and micro-scale porous media. However, for nanoliter droplets imbibition in nanoporous media, the L-W equation may not be suitable, due to the nanoscale liquid-solid interactions, e.g., contact line pinning and capillary condensation. In addition, for an intrinsically hydrophobic nanoporous substrate, spontaneous imbibition of a nanoliter droplet is hypothesized to occur if capillary condensation had occurred internally already.

Experiments: A nanoporous carbon scaffold was synthesized and used as a model nanoporous medium. A recently-developed micro-injection technique was used to generate a series of nanoliter water droplets (2.8-34 nL); the entire wetting dynamics (i.e., apparent contact angle and droplet volume as a function of time) were observed inside an environmental scanning electron microscope.

Findings: The L-W equation does not describe the wetting dynamics of nanoliter water droplets in nanoporous media. A new theoretical model is developed to characterize the corresponding dynamics. It is demonstrated that, even for an intrinsically hydrophobic nanoporous substrate, spontaneous imbibition of a nanoliter droplet can occur if capillary condensation had occurred internally already.

Keywords: Environmental scanning electron microscope; Hydrophobic nanoporous media; Imbibition; Nanoliter droplet; Wetting.