Plasma-assisted growth of polyethylene fractal nano-islands on polyethylene oxide films: Impact of film confinement and glassy dynamics on fractal morphologies
Abstract
Plasma-assisted vapor-phase deposition of (-CH2-)(100) macromolecules is performed onto the surface of pre-deposited polyethylene oxide (PEO). It leads to the formation of two-dimensional 7 nm thick polyethylene (PE) islands of the ramified fractal or ordered dendrite shape.
AFM-infrared nanospectroscopy confirms the phase separation whereas complementary specific heat nanocalorimetry indicates that the crossover from one island shape to another is related to glassy dynamics in underlying PEO. Segmental dynamics is found to be controlled by the thickness of PEO and it manifests in the development of star-shaped PE dendrites on ultrathin (< 30 nm, strongly-confined) PEO.
For thicker (similar to 100 nm, weakly-confined) PEO, the PE islands grow close to a diffusion-limited aggregation regime. Otherwise, segmental mobility in PEO can be controlled by cross-linking which is enhanced under higher discharge power.
The results provide a new physical insight into solvent-free macromolecular diffusion at vacuum/polymer interface and may stimulate the vacuum-compatible development of new polymer-based devices.