Effect of linear elongation on carbon nanotube and polyelectrolyte structures in PDMS-supported nanocomposite LbL films.

Polyelectrolyte (PE) multilayer (PEM) thin films prepared by layer-by-layer self-assembly on flexible substrates are exposed to elongation in many fields of technology. Upon elongation, these types of films are showing interesting, but not understood, phenomena, such as controlled wetting, stimuli-responsive nanovalves, and lithography-free surface structuring. To investigate the mechanisms causing these interesting phenomena, we employed spectroscopic investigations of supported PEM films that were prepared from polystyrene sulfonate (PSS)-wrapped single-walled carbon nanotubes (SWNTs) or pyrene-labeled PSS (PSS-PY) and polydiallyldiammonium chloride. Our results show that the SWNTs agglomerated upon deposition into the PEM and showed a strong change in orientation upon uniaxial elongation of the PEM. Upon release of elongation, the resulting wrinkling pattern was changing its wavelength upon time, in the case of the SWNT-containing PEM. Fluorescence measurements of the PSS-PY in the PEM showed that the PEs changed their orientation due to constant mechanical force from elongation up to a time scale of 2 days after beginning the elongation. The results prove that elongated and released PEM films, until now considered static structures, possess strong kinetics, which has to be taken into account for their application.