Morphological Control of Single-Concave Elastomeric Colloid through Cross-Linking and Osmotic Pressure Variations for Chemical Delivery

In this paper, we propose a convenient and simple method for preparing elastomeric buckled spherical shells through double-emulsion solvent evaporation. In this method, polydimethylsiloxane (PDMS) is added to a water-in-oil-in-water emulsion system and stirred. As the solvent evaporates and the colloid solidifies, the aqueous phase inside formed cavity is squeezed out because of cross-linking stress, or this phase permeates the sphere, leading to loss of the internal water phase and the formation of a single-concave, bowl-shaped shell (i.e., a shell with buckling deformation). We could control the morphology of the produced colloidal particles by varying the concentrations of the permeant and cross-linking agent and the molecular weight of the permeant. Moreover, we propose a mechanism explaining the structural changes occurring during the double-emulsion polymerization process, focusing on cross-linking forces and osmotic pressure. Through leveraging of the shells' reversible swelling properties in solvents, the prepared buckled PDMS shells absorbed Nile red molecules into their cavity, which caused their expansion and restoration. Immersing these shells in ethanol resulted in release of the Nile red molecules. Thus, buckled PDMS shells prepared through the proposed method have potential for application in environmental sensing and drug delivery systems.