Tuning interfacial properties and processes by controlling the rheology and structure of PNIPAM particles at air/water interfaces

In this work, by combining controlled experiments on single interfaces with measurements on solitary bubbles and liquid foams, we show that Poly N-Isopropyl Acrylamide (PNIPAM) microgels assembled at air/water interfaces exhibit a solid to liquid transition changing the temperature, and that this is associated with the change in the interfacial microstructure of the PNIPAM particles around their volume phase transition temperature VPTT. We show that the solid behaves as a soft 2D colloidal glass, and that the existence of this solid/liquid transition offers an ideal platform for tuning the permeability of air bubbles covered by PNIPAM and to control macroscopic foam properties such as drainage, stability and foamability. PNIPAM particles on fluid interfaces allow new tunable materials, for example foam structures with variable mechanical properties upon small temperature changes.