Biomass derived xylose Guerbet surfactants: thermotropic and lyotropic properties from small-angle X-ray scattering

Abstract

A series of novel branched-chain glycosides were synthesised from xylose, an aldopentose and Guerbet alcohols whose total number of carbon atoms ranges from C₈–C₂₄. The thermotropic and lyotropic phases of the highly pure Guerbet xylosides were investigated, using differential scanning calorimetry, optical polarising microscopy and small-angle X-ray scattering. In dry conditions, the shortest compound (total C₈) exhibits a monotropic lamellar (L_α) phase while the C₁₂ compound forms a rectangular columnar (Col_r) phase at room temperature, a rarely reported phase in lipidic systems. The longer ones (C₁₆, C₂₀ and C₂₄) adopt inverse hexagonal (H_II) phases. Upon hydration, the L_α phase of the C₈ compound remains, and while that of the C₁₂ compound exhibits an inverse bicontinuous cubic phase of space group Ia3d in excess water. The C₁₆ and C₂₀ compounds remain in the H_II phase upon hydrating, but the lattice parameters for the hydrated forms increase considerably. An inverse micellar Fd3m cubic phase is observed in the fully hydrated C₂₄ compound. The amphiphilic nature of these compounds coupled with the ability to form inverse non-lamellar phases at room temperature makes them ideal candidates for a variety of applications such as controlled release drug-carriers.