Abstract
The solution behavior in water of some alkyl diglyceryl ethers with different structures (DGE-OMe, IDGE-OMe and IDGE-OH) was investigated through the determination of their binary phase diagrams. Though each alkyl diglyceryl ether formed a lamellar liquid crystalline phase even at low concentrations, their solution behavior was different. In low concentration range, DGE-OMe gave a two-phase region composed of a liquid crystalline phase and a water phase, whereas IDGE-OMe, which is an isomer of DGE-OMe, formed a homogeneous liquid crystalline phase. IDGE-OH with one more hydroxyl group than IDGE-OMe exhibited a solution behavior similar to that of IDGE-OMe.
Fluorescent probe study and thermal analysis on these liquid crystalline phases showed that the planar structure of lamellar liquid crystal of DGE-OMe changed to somewhat a disordered one with increase in water content, while that of IDGE-OMe remained unchanged. The residual area per molecule of DGE-OMe obtained from the surface tension-concentration curve was larger than that of IDGE-OMe.
These facts indicated that this type of surfactants was so less hydrophilic that readily aggregated to form a liquid crystalline phase, and therefore the property of liquid crystal and solution behavior was strongly affected by slight differences in the molecular shape rather than the number of hydroxyl groups.
