Particle Size Controls on Water Adsorption and Condensation Regimes at Mineral Surfaces

Jean-François Boily,Merve Yeşilbaş

doi:10.1038/srep32136

Abstract

Atmospheric water vapour interacting with hydrophilic mineral surfaces can produce water films of various thicknesses and structures. In this work we show that mineral particle size controls water loadings achieved by water vapour deposition on 21 contrasting mineral samples exposed to atmospheres of up to ~16 Torr water (70% relative humidity at 25 °C). Submicrometer-sized particles hosted up to ~5 monolayers of water, while micrometer-sized particles up to several thousand monolayers. All films exhibited vibrational spectroscopic signals akin to liquid water, yet with a disrupted network of hydrogen bonds. Water adsorption isotherms were predicted using models (1- or 2- term Freundlich and Do-Do models) describing an adsorption and a condensation regime, respectively pertaining to the binding of water onto mineral surfaces and water film growth by water-water interactions. The Hygroscopic Growth Theory could also account for the particle size dependence on condensable water loadings under the premise that larger particles have a greater propensity of exhibiting of surface regions and interparticle spacings facilitating water condensation reactions. Our work should impact our ability to predict water film formation at mineral surfaces of contrasting particle sizes, and should thus contribute to our understanding of water adsorption and condensation reactions occuring in nature.

Highlights

Mineral surfaces exposed to water vapour can stabilise thin water films (Fig. 1) of various degrees of organisation and thicknesses[1,2,3], and their mechanisms of formation and growth are the object of an incessantly growing body of literature[4]
In an effort to attempt to generalise these concepts to a wide range of minerals of atmospheric and terrestrial relevance, we explored water vapour binding and condensation reactions on 21 samples of contrasting (i) mineral structure and (ii) composition, (iii) solubility, (iv) particle morphology/crystal habit (v) surface charge, and (vi) particle size/specific surface area (Supplementary Table 1)
We demonstrate the applicability of Hygroscopic Growth Theory (HGT)[35] to account for the size dependence on water vapour binding in the 21 minerals under study, and discuss the implications and limitations of this and competing models in accurately accounting for molecular and thermodynamics aspects of the adsorption and condensation regimes

Summary

Introduction

Mineral surfaces exposed to water vapour can stabilise thin water films (Fig. 1) of various degrees of organisation and thicknesses[1,2,3], and their mechanisms of formation and growth are the object of an incessantly growing body of literature[4] These films are of widespread occurence in nature, and play key roles in atmospheric, terrestrial and astronomical processes[5,6,7,8]. FTIR spectroscopy provided, at the same time, new insight into the hydrogen bonding environments adapted by thin water films in submicron- in relation to micron-sized minerals These latter efforts notably build upon a recent study in our group focused on the properties of thin ice films formed in the same 21 mineral samples used of this study[34]. We demonstrate the applicability of Hygroscopic Growth Theory (HGT)[35] to account for the size dependence on water vapour binding in the 21 minerals under study, and discuss the implications and limitations of this and competing models in accurately accounting for molecular and thermodynamics aspects of the adsorption and condensation regimes

Methods

Results

Conclusion