Aqueous foams stabilized by temperature-sensitive hairy polymer particles

Abstract

Submicrometer-sized polystyrene (PS) particles carrying poly[2–(diethylamino)ethyl methacrylate] (PDEA) hairs (PDEA–PS particles) were synthesized by free radical dispersion polymerization. The hydrophilicity–hydrophobicity balance of the PDEA could be tuned by varying the temperature at near neutral pH (a lower critical solution temperature of PDEA at pH 6.86, 41 °C) and therefore these sterically-stabilized particles acted as temperature-sensitive stabilizers for aqueous foams. At 25 °C, where the PDEA hairs were hydrated and PDEA–PS particles were colloidally stable in aqueous media, foams were formed which coalesced with time and the size of the bubble increased. At 40 and 45 °C, where the PDEA hairs were partially non-hydrated and PDEA–PS particles were close to flocculation or weakly flocculated, foams were formed and bubble coalescence and size increase speeds were slower than those observed at 25 °C. At and above 50 °C, where the PDEA hairs were non-hydrated and PDEA–PS particles were heavily flocculated in aqueous media, the more stable cream-like foams whose volume was almost the same for 1 week were formed. Scanning electron microscopy studies indicated that the particles mainly adsorbed at the air–water interface as monolayers at 25 °C and as multilayers at and above 40 °C. The foam stability and structure could be controlled by changing the temperature.