Effect of glycols on the self-assembly of amphiphilic block copolymers in water. 2. Glycol location in the microstructure

The effects of cosolvents on the microstructure of the lyotropic Liquid cry stals formed by poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene ox ide) (PEO-PPO-PEO) triblock: copolymers in water were examined in ternary i sothermal systems consisting of a representative PEO-PPO-PEO copolymer (Plu ronic P105, (EO)(37)(PO)(58)(EO)(37)), water, and a polar cosolvent (glycer ol; propylene glycol, ethanol, or glucose, referred to as "glycols"). The c haracteristic length scales of the lyotropic liquid crystals were establish ed using small-angle X-ray scattering (SAXS). The SAXS data are analyzed an d discussed with respect to (i) influence of the different glycols and the glycol content on the characteristic length scales, (ii) area occupied by o ne macromolecule at the polar/apolar interface, (iii) location of the diffe rent; glycols in the microstructure, and (iv) glycol ability to modify the interfacial curvature through swelling the PEO-PPO-PEO macromolecule to dif ferent extents. The trends in the glycol effects observed in the ternary ph ase diagrams ("macroscopic" information) are confirmed and reinforced by th e detailed microstructural information obtained here by SAXS. A correlation is found between the glycol effect on the microstructure of the lyotropic liquid crystals (the degree of relative swelling) and the glycol polarity ( expressed in terms of octanol/water partition coefficient, dielectric const ant or solubility parameter).