Liquid Crystal Structural Variability on Water/Mixed Nonionic Surfactants/Caprylic-Capric Triglyceride Systems

Abstract

The systems investigated by small angle x-ray scattering (SAXS), and polarized microscopy were water/sucrose laurate/ethoxylated mono-di-glyceride/oleic phase. The oleic phase was caprylic-capric triglyceride or caprylic-capric triglyceride + ethanol. The mixing ratios (w/w) of sucrose laurate/ethoxylated mono-di-glyceride and ethanol/caprylic-capric triglyceride equal unity. SAXS experiments demonstrate the presence of lamellar (L_α) liquid crystals. The size of the nonpolar compartment, the thickness of the hydrophilic mantle, and the available surface area per mixed surfactants headgroups of the lamellar (L_α) liquid crystals were estimated as a function of oleic phase content. The size of the nonpolar compartment decrease with the increase in the oleic phase content (decrease of water content). The alcohol free system has higher values of the size of the nonpolar compartment compared to the alcohol based system. The thickness of the hydrophilic mantle also decreases with the increase in the oleic phase content. The alcohol free system has lower values of the thickness of the hydrophilic mantle compared to the alcohol based system. The available surface area per mixed surfactants headgroups increases with increasing the oleic phase content. The available surface area per mixed surfactants headgroups in the system free of alcohol is considerably smaller than that in the alcohol based system. The difference in the behaviour between the alcohol free and alcohol based systems is interpreted by the disordering effect of the mesophase by the presence of alcohol in system.

Keywords:

• Available surface area per surfactant headgroup
• lamellar liquid crystal
• periodicity
• scattering intensity
• size of the nonpolar compartment
• small-angle x-ray scattering (SAXS)
• thickness of the hydrophilic mantle

Notes

φ_P is the volume fraction of the polar components of the system. (a_o)_L is the available area per surfactant molecule in the lamellar mesophase determined at the interface between the polar and nonpolar regions. N_S is the mole number of the surfactant; N_A is Avogadro's number and the total volume V_T is expressed in ų.