Solubilization of Nonionic Polymers in a Lyotropic Lamellar Mesophase: Lecithin-Water-Polyethylene Oxide System

Abstract

Soybean lecithin forms a homogeneous lamellar liquid crystalline phase with water at concentrations of less than 33 wt% water. The solubilization of water-soluble polyethylene oxide polymer into the lamellar phase is studied by 2 H and 31P NMR and polarizing microscopy methods. Between 20 and 33 wt% of water, the liquid crystalline phase is unable to solubilize any appreciable amounts of polymer and the mesophase is destabilized by the addition of about 0.5% of polymer, whereas the solubilization of the polymer increases drastically in the lamellar phase (e.g., 18% polymer at 10% water) with water content less than 10%. The 2H NMR quadrupole splitting values, as well as the 31P NMR chemical shift anisotropy, remain unaffected by replacement of lecithin or water with polymer. The results indicate that the binding of water to the interface and the molecular organization of the choline headgroup are little affected by the presence of polymer molecules in the mesophase.