Formation of Surface Wrinkles in Collapsed Langmuir Films of a Polyhedral Oligomeric Silsesquioxane Containing Diblock Copolymer.

Surface pressure versus mean molecular area isotherms of Langmuir films of a hybrid diblock copolymer of poly(ethylene glycol) (PEG) and poly(methacrylo polyhedral oligomeric silsesquioxane) P(MA-POSS) together with Brewster angle microscopy reveal details of the phase transitions. The formation of a periodic wrinkling pattern in collapsed films is observed by epifluorescence microscopy after applying several compression-expansion cycles above the surface pressure of ≈18 mN/m. The wrinkle formation is reversible upon compression and expansion of the Langmuir films. Two distinct orientations of POSS molecules are assumed in Langmuir films upon compression, vertically for chains close to the water surface and horizontally orientated upper layers with significant amounts of PEG in between them. Thus, the wrinkling forms mainly in the top stiffer MA-POSS blocks above a certain compressional stress. The wrinkles disappear during the Langmuir-Blodgett (LB) transfer. Nevertheless, atomic force microscopy and grazing incidence wide-angle X-ray scattering experiments reveal the formation of highly ordered POSS molecules in LB films.