The inverse hexagonal to inverse ribbon phase transition in a mixed phosphatidylcholine-phosphatidylethanolamine system at low hydration is studied using small and wide angle X-ray scattering. It is found that the structural parameters of the inverse hexagonal phase are independent of temperature. By contrast the length of each ribbon of the inverse ribbon phase increases continuously with decreasing temperature over a range of 50° C. At low temperatures the inverse ribbon phase is observed to have a transition to a gel lamellar phase, with no intermediate fluid lamellar phase. This phase transition is confirmed by differential scanning calorimetry
