Surfactant and polyelectrolyte gel particles for encapsulation and release of aromatic oils

Associative phase separation occurs when oppositely charged surfactants and polyelectrolytes are mixed in near-stoichiometric proportions. This behavior has been exploited in the production of gel particles that range between approximately 100 and 4000 μm in diameter. Here, we investigate their performance as materials for the encapsulation and release of the aromatic oil cymene. The gel particles (ca. 1500 μm in diameter) are prepared by dropwise addition of an oil-in-water suspension made of cymene droplets dispersed in a viscous solution of sodium dodecyl sulfate (SDS) and N,N,N-trimethylammonium derivatized hydroxyethyl cellulose (JR-400™) to a gelling solution of excess SDS. The release of cymene into aqueous (5 wt.% SDS and 4 wt.% pentanol in water) and organic (isooctane) solutions is measured using UV-VIS spectroscopy and analyzed with the shrinking core model. The experimental data and model analysis indicate that the release rate is determined by the effective diffusivity and solubility of the oil in the aqueous gel matrix, both of which depend on the presence of surfactant in the receiving solution, and the swelling of the gel particle.