Effects of Chain Length on the Thermotropic and Lyotropic Phase Behaviours of Maltosides by Small-angle X-ray Diffraction Study 

Industrially useful surfactants such as alkyl polyglucosides (APGs) and synthetic branched-chain glycosides are interesting biosurfactants and offer an interesting insight into life-science applications. Hence, research presented here a study of the thermotropic and lyotropic phase of 2-hexyldecyl β-D-maltoside (β-Mal-C₁₀C₆) and the corresponding 2-decyltetradecyl β-D-maltoside (β-Mal-C₁₄C₁₀) over a range of temperatures (0–80 °C). Small-angle X-ray diffraction (SAXS) and optical polarizing microscopy (OPM) have been used to characterize the mesophase behaviour. This study has shown that in dry conditions β-Mal-C₁₀C₆ and β-Mal-C₁₄C₁₀ adopt a lamellar crystalline phase (L_c), on the other hand, in excess water these compounds form a fluid lamellar phase (L_α) upon heating and cooling. The study also reported the effects of temperature (0–80 °C) on the d-spacing value using SAXS, and we estimated the surface area  per molecule and water content of the fluid lamellar phase (L_α) in the fully hydrated state for both β-Mal-C₁₀C₆ and β-Mal-C₁₄C₁₀. The former gave the surface area per molecule and water content of  57 Å² and 25 wt % respectively,  however, the latter forms 69 Å² and 20 wt %.