Phase transitions in monolayer formed by hyperbranched polyester with alkyl-terminated branches at the air/water interface

Investigations of Langmuir and Langmuir–Blodgett molecular films of hyperbranched polyester with alkyl-terminated branches over a wide temperature range revealed an unusual phase transitions. The measured surface pressure–surface area isotherms clearly show that the hyperbranched polyester formed stable and well-defined monolayers at the air/water interface. At temperatures below 313 K ice floe-like structures of a condensed phase were formed already from very low surface pressures. On the increase of the surface pressure the floes of the condensed phase merged forming a uniform monolayer. Above 313 K a surface liquid phase was formed at the interface. It was shown that the phase transition from the surface liquid phase to the condensed phase occurred on temperature decrease. At lower temperatures the compression process was not reversible. The increase of temperature up to about 323 K made the compression process reversible. The monolayers were transferred from the air/water interface onto silicon and mica substrates using the Langmuir–Blodgett technique at different temperatures. The structure of the polyester monolayer formed at the substratesʹ surfaces was investigated.