Surface pressure isotherms and ellipsometric measurements of monolayers of two triblock symmetric copolymers, poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO), at the air−water interface have been carried out. These copolymers are water-soluble, and the difference in hydrophobicity between the blocks is small. This represents a different scenario for brush formation than for most of the hydrophobic−hydrophilic block copolymers reported so far. The surface pressure curves show two different phase transitions. The ellipsometric measurements indicate a thickness transition when the monolayer saturates, which supports the hypothesis for brush formation. The experimental data have been analyzed in terms of the scaling theory of adsorption of polymer brushes. Despite the possibility of diffusion from the interface, the PPO block acts as an efficient anchoring element in the formation of an adsorbed brush, once the adsorption sites at the interface are fully occupied. This is analogous to what has been reported for diblock copolymers with a much larger difference in the hydrophobicity of the blocks.

Dynamic surface tension (DST) experiments have been combined with time-resolved ellipsometry (TRE) to study the adsorption kinetics of symmetric triblock copolymers at the air−water interface. The equilibrium behavior of these adsorbed monolayers has been studied in the preceding paper in this issue (part 1), pointing out evidence for brush formation at sufficiently high surface concentrations. The dynamic results are consistent with a diffusive mechanism delayed by adsorption barriers in the full adsorption regime at lower concentrations. The first-order phase transition scenario evidenced from the equilibrium results is now also perceptible from the dynamic results:  a competition between the bulk diffusion and molecular reorientation mechanisms is found in the brush regime. This two-step adsorption kinetics is characterized by an intermediate plateau, dγ(t)/dt = 0, which gives evidence for phase coexistence while final steady-state equilibrium is attained.