Formation of microemulsion and liquid crystal in biocompatible sucrose alkanoate systems

Sucrose monoalkanoates (SE) form microemulsions by mixing with lipophilic c osurfactants such as the middle-chain alcohols, or sucrose polyalkanoates. In the case that sucrose monododecanoate is combined with hexanol, a middle -phase microemulsion is produced and coexists with excess water and oil pha ses at optimum mixing fraction of SE and hexanol. The bicontinuous structur e of the microemulsion was confirmed by means of self-diffusion coefficient on NMR measurement. A larger solubilization capability of oil is attained to a mixed mono- and poly-dodecanoate system than that of the middle-chain alcohol. It is probab ly due to the location of most of surfactant molecules at the micro-interfa ce inside the microemulsion. In this system, instead of forming a three-pha se region, a lamellar liquid crystal intrudes into multi-phase region since the surfactant layer is rather rigid as which was supported by the results of SAXS and ESR measurements. Further addition of a short-chain alcohol su ch as propanol to the mixed system leads to the flexible interface, as a co nsequence three-phase microemulsion with large solubilization is formed.