Langmuir monolayers of non-ionic polymers: equilibrium or metastability? Case study of PEO and its PPO-PEO diblock...

Stability and reorganization in Langmuir films of PEO in PEO homopolymers and PPO-PEO block copolymers were investigated using film balance measurements. The apparent fractional losses of EO segments transferred into the subphase resulting from successive compression-expansion cycles have been estimated. The apparent loss is mainly Γ(max), M(n) and time-dependent. At surface concentrations Γ⩽0.32 mg/m(2), PEO films are in equilibrium. For 0.32⩽Γ⩽0.7 mg/m(2), the losses remain modest. Further compression leads to densification of the monolayer, requiring the interplay of thermodynamics and kinetic factors In the plateau regime, the loss is higher and constant for 1⩽Γ(max)⩽2 mg/m(2) upon maintaining the achieved surface area for 15 min. Similar losses were obtained for PEO homopolymers of high Mn and PPO353-PEO2295. It suggests that the PEO remains anchored in a metastable state at the air-water interface at surface concentration well above the onset of the plateau. Additional losses are incurred for PEO homopolymers for monolayers kept compressed in the plateau for 2 h. For the interpretation of these phenomena a combination of elements from self-consistent field theory and scaling is desirable with as a trend an increasing contribution of the latter with increasing surface concentration.