Novel controllable auxetic effect of linearly elongated supported polyelectrolyte multilayers with amorphous structure.

Polyelectrolyte multilayers (PEMs) deposited on flexible supports are promising candidates for many applications ranging from controlled wettability over stimuli responsive nanovalves to lithography free surface structuring. Since many potential applications involve elongation of these films, we investigated the effect of elongation on the PEM thickness and density with ellipsometry. To our surprise PEM films with known amorphous internal structure show auxetic behavior that depends on the PEM preparation condition. The measured refractive index was compared with simulated values using the Garnet equation to evaluate if the incorporation of water or air causes the observed phenomena.