Langmuir polymer films: recent results and new perspectives

Langmuir polymer films (LPFs) are very interesting systems to probe quasi-two dimensional dynamics. Although adsorbed on water, the substrate is fluid enough to avoid irreversible pinning at adsorption sites, as with solid substrates. LPFs in dense states can exhibit a high degree of metastability, however reproducible measurements can be performed on films which have not been previously compressed. The shear rheology is one of the most active fields of research, especially because it allows investigation of flow behaviour in LPFs, thus of possible reptation motion in semidilute films under good solvent conditions. It also allows probing glassy behaviour in dense films under poor solvent conditions. In this perspective article, we review the recent literature and discuss unpublished results on the dynamics of the glass transition, recently observed in these quasi-2D systems at low temperatures. We conclude by listing new problems and open questions emerging from this research area.