Monolayers of a solvent-free polymer brush: Part 1. Thermodynamics at the air/water interface

Hydrophobie polymers with low glass transition temperature (polyisoprenes) and a single head group (sulfonate) have been synthesised and characterised as insoluble monolayers on a water surface. A single ionic head group is sufficient to make these hydrophobic polymers surface-active and isotherms of an expanded type have been recorded. These isotherms can be described quantitatively by using a theory based on constant density of the hydrophobic region, Gaussian chain statistics and affine deformation: at a fixed area per head group, the surface pressure is proportional to the length of the hydrophobic tail. The slope of this relationship is proportional to the third power of the area per head group. Chains shorter than 300 repeat units exhibit a systematic deviation from the theory.