Equilibrium and Dynamic Surface Tension Behavior of Triblock Copolymer PEO-PPO-PEO in Aqueous Medium

Abstract

Equilibrium surface tension of water-soluble triblock copolymer PEO-PPO-PEO (Pluronics) has been measured to determine critical micelle concentration (CMC). The equilibrium surface tension data have been fitted with Langmuir adsorption isotherm. Dynamic surface tension (DST) of the polymer solutions has been measured at below and above the CMC. Results have been compared with the data of a typical nonionic surfactant C12E9. Significant difference in behavior of DST has been observed, with the P123 showing very slow relaxation below the CMC. Above CMC, DST data of P123 show a long induction period. However, relaxation time has been found to be comparable to C12E9. Ward and Tordai model with Langmuir adsorption isotherm has been used to fit the DST data of P123. Similarly C12E9 data from the literature have been fitted with Ward and Tordai model. A reasonably good fit has been obtained for C12E9, although the long-time data deviate from the model. The model has been found to be inadequate for the triblock copolymer that has been attributed to the change in configuration of the polymer at the surface after adsorption.