Effects of temperature and concentration on the structure of ethylene oxide-propylene oxide-ethylene oxide triblock copolymer (Pluronic P65) in aqueous solution: a molecular dynamics simulation study

The effects of temperature and solution concentration on the structure of triblock polymeric surfactant (ethylene oxide)(19)(propylene oxide)(29)(ethylene oxide)(19)(Pluronic P65) have been investigated by fully atomistic molecular dynamics simulations. The Flory-Huggins interaction parameter x, hydrogen bonding and molecular mobility in the aqueous solution of P65 were investigated covering a composition range of 0.1-0.73 (water weight fraction) and a temperature range of 273-373 K. The Flory-Huggins parameters indicated that propylene oxide (PO) segments became hydrophobic with the increase in temperature, whereas ethylene oxide (EO) segments remained hydrophilic, which caused the increase in repulsion between EO and PO segments. The intermolecular hydrogen bonds in P65 solution including water-water hydrogen bonds and water-P65 hydrogen bonds increased with the increase in solution concentration and decreased with the increase in temperature. The critical micellar temperature of Pluronic P65 predicted by Flory-Huggins interaction parameter x and hydrogen bonding was in good agreement with experimental data.