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.