Adsorption of PNIPAm110-PEO100-PPO65-PEO100-PNIPAm110 pentablock terpolymer on hydrophobic gold

The adsorptions of a double thermo-sensitive pentablock terpolymer, PNIPAm110-PEO100-PPO65-PEO100-PNIPAm110 (PNIPAm110-F127-PNIPAm110), on hydrophobic gold surfaces at various temperatures were investigated by using quartz crystal microbalance (QCM), atomic force microscopy (AFM), and ellipsometry. The experimental results indicated that the adsorption kinetics, adsorbed amounts and morphologies of the adsorbed terpolymer layers were strongly dependent on the temperatures, which could be correlated with the chain conformation of PNIPAm110-F127-PNIPAm110 in aqueous solution. At the low critical solution temperature (LCST) of PPO block (i.e. 31 °C), PNIPAm110-F127-PNIPAm110 was adsorbed onto hydrophobic gold surface via a two-step adsorption process and adopted a brush-like conformation. While at the LCST of PNIPAm block (i.e. 34 °C), a complex multistep adsorption process was observed, which resulted in a large adsorption amount. By comparing with the adsorption behavior of F127 at the corresponding temperature, it was deduced that the large adsorption amount obtained at 34 °C was mainly attributed to the presence of PNIPAm blocks. The premicellar associative adsorption was thought to play an important role for the observation of this unexpected adsorption behavior at 34 °C, leading to the large adsorption amount and large aggregate structures as revealed by AFM.