The release of volatile oil has relevance to the diffusion. This is
similar in principle of pervaporation. In this mechanism, volatile
oil is released by partial vaporization through porous membrane.
Diffusion is controlled by the permeability of core material through the membrane of particles. Membrane permeability is
affected by the permeating molecules and the chemical properties
of membrane, its morphology, and its transition temperature.
Furthermore, the driving force for diffusion is related to the vapor
pressure of volatile oil (Reineccius 1995). As stated above, we
could find that the release rate of thyme oil was accelerated by
the porous surface of microcapsules and high storage temperature.
Thus these results indicate that the sustained release properties of
microcapsules can be controlled by the emulsifier types as well as
storage temperatures.