Thermotropic phase behavior and surface-active properties of alkoxyethyl α-d-glucopyranoside

Abstract

To overcome the inherent weakness of the traditional alkyl α-d-glucopyranoside in water solubility and surface activity, a series of sugar-based surfactants alkoxyethyl α-d-glucopyranosides were successfully synthesized by introducing an oxyethene spacer (OCH2CH2). Herein, their thermotropic liquid crystalline and surface-active properties were investigated using DSC, POM and other methods. The phase transition temperature increased with increasing the alkyl chain length, meanwhile all glycosides were found to form the smectic phase since there was the typical focal-comic fan texture during cooling. Moreover, alkoxyethyl α-d-glucopyranosides had better water solubility and finer surface activity than that of the traditional alkyl α-d-glucopyranosides without an oxyethene fragment. Furthermore, the HLB number, solubility, CCMC value, γCMC value and Γmax value of alkoxyethyl α-d-glucopyranoside had a tendency to decrease with increasing the alkyl chain length, whereas the logP value, πCMC value, Αmin value and pC20 value showed the opposite trend with increasing the alkyl chain length. In addition, decyloxyethyl α-d-glucopyranoside showed the strongest emulsifying activity in n-octane/water system and rapeseed oil/water system, and it also had the best foaming properties. Therefore, an effective introduction of an oxyethyl fragment as a hydrophilic spacer indeed made an excellent contribution to improve water solubility and surface activity.