The effect of anomeric head groups, surfactant hydrophilicity, and electrolytes on n-alkyl monoglucoside microemulsions

The effects of the variables of head group structure and salt concentration on microemulsions formed in mixtures of water, alkyl ethylene glycol ethers (C(k)OC₂OC(k)), and n-alkyl β-D-glucopyranosides (C(m)βG₁) are explored. Phase behavior of mixtures containing an anomer of the surfactant (n-alkyl α-D-glucopyranoside, C(m)αG₁), or surfactants with long head groups (n-alkyl maltopyranosides, C(m)G₂), or NaCl or NaClO₄ as electrolyte are systematically reported as a function of temperature and composition. The substitution of n-alkyl α-D-glucopyranosides for n-alkyl β-D-glucopyranosides causes precipitation under some conditions in all mixtures studied. These solubility boundaries begin in the water-surfactant binary mixture at the Krafft boundary, then extend to high concentrations of both surfactant and oil. Increasing the effective length of the surfactant head group by adding C(m)G₂ to water-C(k)OC₂OC(k)-C(m)βG₁ mixtures moves the phase behavior dramatically up in temperature when even small amounts of C(m)G₂ are used. Adding a lyotropic electrolyte, NaCl, to water- C(k)OC₂OC(k)-C(m)βG₁ mixtures moves the phase behavior down in temperature, while the hydrotropic electrolyte NaClO₄ moves the phase behavior up in temperature.