Surface tensions of aqueous solutions of 1-O-monoacyl sugar alcohols

Surface tension curves were measured using the Wilhelmy method for the monoacyl glycerols, erythritols and xylitols with the acyl chain lengths of 8, 10, 12 and 14 at 25, 32 and 39 °C. The curves were also measured for the monolauroyl esters of arabitol, ribitol and sorbitol. The critical micelle concentration, CMC, for a series of sugar alcohol esters with different acyl chains decreased as the chain length increased. The numbers and orientations of the hydroxyl groups of the sugar alcohols with the monolauroyl residue did not affect the CMC, while the surface tension at the CMC, γCMC, increased as the number of hydroxyl groups increased except for the monoacyl xylitols. The residual area per molecule was also independent of the types of hydrophilic and hydrophobic moieties, and was in the range of 0.3–0.4 nm2. The CMC values did not depend on the temperature for any of the tested monoacyl sugar alcohols, indicating that the enthalpy of the micellization was nearly zero. Because the free energy of the micellization was negative for every ester, the entropy of micellization was positive.