Rheological Study of Order-to-Disorder Transitions and Phase Behavior of Block Copolymer–Surfactant Complexes Containing Hydrogen-Bonded Small Molecule Additives

Abstract

Dynamic mechanical measurements were used to investigate the effect of small molecule additives on the order-to-disorder transitions (ODTs) of Pluronic, poly(ethylene oxide) (PEO)–poly(propylene oxide) (PPO)–PEO triblock copolymer surfactant melts. The small molecule additives contain multiple functional groups (carboxyl or hydroxyl), which selectively interact with the PEO component of Pluronic via hydrogen bonding, thereby effectively increasing χ of the system and leading to microphase separation in otherwise disordered melts. The ODTs of these Pluronic/small-molecule-additive complexes can be detected by rheology since, upon increasing temperature, crossing the order-to-disorder transition temperature (TODT) results in a sharp decrease in the low frequency storage and loss moduli (G′ and G″, respectively). The crystallization of the PEO component is suppressed with increasing additive loading due to strong hydrogen bond interactions. The TODT is strongly composition dependent and increases up to 145 °...