Buckling of charged diblock copolymer monolayers at the air-water interface

Langmuir films of charged-neutral diblock copolymers spread at the air/water interface were studied. A reversible buckling instability of large characteristic size (10 μm range) is evidenced while compressing the films. A complete characterization of this phenomenon with respect to the polymer length was accomplished using optical microscopy and X-ray surface scattering. The polymer sub-phase concentration appears to control the instability threshold in surface pressure. In order to explain the observed linear variation of the buckling wavelength with the polymer mass, an analogy with the wrinkling of elastic layers is proposed.