Hydrophobically Covered Hydrogels: Preparation Approaches and Possible Applications

This article overviews methods for preparation of micrometer-sized particles having hydrogel core and hydrophobic shell. It demonstrates that water-in-oil inverse suspension polymerization is a versatile method for one-step synthesis of either non-hollow spherical hydrogel particles or hollow capsules, depending on the nature of the gel-forming polymer. It further shows that rather thin hydrophobic shell provides a good stability of the particles in organic solvents while still does not preclude swellability of the hydrophilic core with water and small water-soluble molecules. A stepwise approach for fabrication of the core-shell hydrogel particles is also described which assumes preparation of hydrogel particles as the first step, their arrangement on surfaces followed by growing of the hydrophobic shell. Two methods for preparation of the hydrophobic shell were explored. The first one assumes free-radical polymerization of the polyisoprene from adsorbed hydrogel particles while the second one implies electrostatically-driven adsorption of polyisoprene latex particles onto oppositely charged hydrogels. Thus-obtained core-shell particles were used in fabrication of switchable coatings.