Abstract
Differential scanning calorymetry (DSC) was conducted to clarify the crystallization behavior of n-hexadecane dispersed in oil-in-water emulsions (n-hexadecane : water=20 : 80). Tween 20 was used for emulsification and four sucrose fatty acid esters; sucrose laurate (L-195), sucrose palmitate (P-170), sucrose stearate (S-170) and sucrose oleate (O-170) were added to n-hexadecane. Crystallization temperature (Tc) of n-hexadecane in the emulsion system was 3.4°C and the melting temperature (Tm) was 17.4°C. Tc and Tm were 16.9°C and 18.5°C for bulk n-hexadecane, respectively. P-170 and S-170 addition resulted in considerable increase in Tc of n-hexadecane/water emulsions but L-195 had only slight effect. O-170, possessing oleic acid moieties as its hydrophobic portion had no effect on Tc of n-hexadecane/water emulsions. In bulk liquid, none of the sucrose esters showed any effect on Tc or Tm of n-hexadecane.
With the addition of P-170 and S-170, small endothermic peaks appeared at 3.6°C and 4.1°C (on heating) and exothermic peaks at -3.2 and -3.0°C (on cooling) appeared in addition to the crystallization and melting peaks of n-hexadecane. These peaks corresponded to phase transitions of molecular aggregates formed emulsion interfaces. The mechanisms for acceleration of crystallization of n-hexadecane and molecular aggregate formation are discussed with consideration to interface adsorption and mesophase formation due to sucrose fatty acid ester addition in n-hexadecane.
