  Colloidosomes provide a possibility to encapsulate oily substances in water
in the form of core-in-shell structures. In this study, we produced
microcapsules with shell from colloidal particles, where the interparticle
openings are blocked by mixed layers from polymer and surfactant that prevent
the leakage of cargo molecules. The particles and polymer play the role of
bricks and mortar. We used hydrophilic silica particles, which were partially
hydrophobized by the adsorption of potassium oleate to enable them to stabilize
Pickering emulsions. Various polymers were tested to select the most
appropriate one. The procedure of encapsulation is simple and includes single
homogenization by ultrasound. The produced capsules are pH responsive. They are
stable in aqueous phase of pH in the range 3-6, but at pH>6 they are
destabilized and their cargo is released. With the optimized formulation of
silica particles, polymer, oleate and NaCl, we were able to encapsulate various
oils and fragrances, such as tetradecane, limonene, benzyl salicylate and
citronellol. All of them have a limited and not too high solubility in water.
In contrast, no stable microcapsules were obtained with oils that either have
zero water solubility (mineral and silicone oil) or higher water solubility
(phenoxyethanol and benzyl alcohol). By analysis of results from additional
interfacial-tension and thin-film experiments, we concluded that a key factor
for obtaining stable capsules is the irreversible adsorption of the polymer at
the oil/water interface. The hydrophobization of the particles by surfactant
adsorption (instead of silanization) plays an important role for the pH
responsiveness of the produced capsules.
