This agrees with previous studies of the GMO/water system. In the temperature range from 80 to 95 °C, the reflections from the H2 structure dominate the scattering. The calculated lattice constant was 5.3 nm, similar to what has been reported in previous studies. The lattice parameter of the mesophases decreases with increasing temperature owing to the reduction of the effective headgroup area of GMO at the interface from dehydration. The integration of 5wt% HEA into this Pn3m-type bicontinuous cubic bulk phase was then compared to the structures without HEA. The corresponding SAXS patterns of GMO60HEA5W35 are presented in Figure . Integrating 5 wt% HEA into the system transforms the Pn3m-type bulk phase into the Ia3d-type structure at 35 and 40 wt% water content with a lattice constant of 14.6 nm and 17.1 nm at 25 °C, respectively. The formation of Ia3d structure was previously reported between 17 and 32wt% of water content at 25 °C. Concerning the coexisting structure at and below 25 °C, peaks are observed with SAXS at q = 1.25, 2.50 and 5.20 nm -1 . These reflections correspond to a coexisting lamellar structure with a d-spacing of 2π/q1 = 4.7 nm. The formation of lamellar structure in the GMO bulk phase was reported at water below 20 wt%. The presence of the Ia3d and lamellar structure in the samples with 35 and 40 wt% water indicates that HEA integrates into the interfacial region of the structures, participating in the self-assembly.