Super-hydrophobic powders obtained by froth flotation: properties and applications

Abstract

Super-hydrophobic materials offer a wide range of industrially relevant applications such as water-repellent construction materials, surface or textile coatings and oil sorbents. Hydrophobic modification of mineral particles is at the heart of the froth-flotation process. I show here that froth-floated fluorite crystals display super-hydrophobic properties: they form highly stable monolayers on flat and curved (“liquid marble”) water surfaces, surround themselves with a gaseous plastron when submerged and selectively disperse and increase the density of oil in an oil–water mixture. I show that resuming the main steps of the flotation process using oleic acid functionalization provides an easy way to render low-solubility calcium salts (CaCO₃, CaF₂) hydrophobic. I study the potential of hydrophobic crystal monolayers to mitigate freshwater evaporation losses for water management: surprisingly, I find that even very compact, polydisperse crystal layers do not reduce water evaporation rates. I finally present a new method based on hydrophobic modification and X-ray scanning at an air–liquid interface to determine the cleavage planes of ground mineral powders with potential applications in mineralogy and catalysis.