Effects of temperature and chemical modification on polymer Langmuir films

We previously reported on a rheological study of Langmuir films of poly(tert-butyl methacrylate) (PtBMA), and this work describes further studies on this system. Here, surface pressure-area (Pi-A) isotherms and interfacial shear rheology experiments are performed to better understand the effects of two modifications: varying the temperature between 5 and 40 degrees C and introducing small amounts of carboxylic acid groups by partially hydrolyzing the polymer. Increased temperature produced isotherms with lower plateau surface pressures, Pip, and Pi values shifted to lower areas above Pip. Film properties transition from being primarily viscous to being dominated by elasticity as Pip is crossed for all temperatures studied, even as the value of Pip changes. Increasing the hydrolysis fraction leads to isotherms shifted to lower areas throughout the curve and higher Pip values. Both temperature variation and chemical modification are believed to affect the relative importance of polymer-polymer and polymer-subphase interactions.