Molecular interactions in lyotropic reverse hexagonal liquid crystals: A dielectric spectroscopy study

A dielectric study of reverse hexagonal mesophases (H_II) is presented. Conducted in the frequency range 0.01 -1 MHz and temperature range 293 < T < 319 K, the study reveals complex molecular behavior in and around the interfaces of the mesoscopic structures of the gel. There exist three clearly defined dielectric relaxations related to separate moieties in the interface, as well as a temperature-activated dc conductivity. A critical temperature, T₀ = 307 K, is noted in the results and related to the dehydration of the glycerol monooleate (GMO) head groups. Effectively, this represents a breakdown of the interfacial layer of water. The consequences of this act are clearly visible in the change in behavior of the fitting parameters for all processes. A physical picture emerges whereby at T₀ = 307 K, the "loosening " of the GMO heads accentuates the dangling motion of the phosphatidylcholine (PC) tails, evidenced by counterion motion along the PC head. Furthermore, it precipitates the percolation of the large TAG molecules that are intercalated in the GMO and PC tails.