Effect of glycols on the self-assembly of amphiphilic block copolymers in water. 1. Phase diagrams and structure identification

The effects of cosolvents such as glycerol, propylene glycol, ethanol, or g lucose (referred here as "glycols") on the phase behavior of a representati ve poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (PEO-PPO -PEO) triblock copolymer (PluronicP105, (EO)(37)(PO)(58)(EO)(37))are presen ted. Regions of lamellar, bicontinuous cubic, hexagonal, and micellar cubic lyotropic liquid crystalline structures (established from small-angle X-ra y scattering measurements) have been delineated in the four ternary isother mal (25 OC) PEO-PPO-PEO-water-glycol phase diagrams. Pronounced effects on the concentration range of stability of the different phases we're found wh en the glycol was varied from ethanol (the least polar glycol examined here ) to glucose (the most polar). For example, glycerol and glucose swell the hexagonal phase to lower copolymer content, while propylene glycol and etha nol do not show this effect. Our experimental observations are discussed in terms of modification of the system "interfacial curvature" affected throu gh the ability of different glycols to swell the PEO-PPO-PEO macromolecule to different, extents. A hypothesis is proposed, based on a correlation bet ween the PEO-PPO-PEO-water-glycol phase behavior and the glycol polarity, t o account for and predict the effect of glycols on the ternary phase behavi or of PEO-PPO-PEO block copolymers.