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.