Kinetics of Adsorption and Desorption of PEO−PPO−PEO Triblock Copolymers on a Self-Assembled Hydrophobic Surface

We report on the kinetic behavior of adsorption from solution of a family of triblock copolymers, copoly(ethylene oxide−propylene oxide-ethylene oxide) (PEO−PPO−PEO), on a gold surface modified by a methyl-terminated, self-assembled monolayer (SAM) of a long-chain alkanethiol (CH 3 (CH 2 ) 10 SH). We monitored the kinetics with a surface plasmon resonance (SPR) technique, whose fast time resolution (0.1 s) allowed us to follow the evolution of these systems even for characteristic times of a few seconds. The data were analyzed in the context of a mass transfer corrected Langmuir kinetics model. While the model is only able to reproduce the observations for either very dilute solutions or the initial stages of the process, it nevertheless allows us to discriminate the onset of the different mechanisms of adsorption. This study shows that, for a series of compounds with the same length of the PPO block, the intrinsic kinetics of the adsorption process is affected by the relative balance of the hydrophilic and hydrophobic content within the copolymer: higher hydrophobic content leads to enhanced adsorption rates past the critical micelle concentration (cmc). This is consistent with observations from our earlier study on the morphology of the polymer-coated surfaces by atomic force microscopy.