Elastic Moduli of Asymmetric Ultrathin Free-Standing Polyelectrolyte Nanocomposites

Abstract

We have developed a novel technique for the elucidation of the mechanical behavior of ultrathin free-standing materials and demonstrate results using polyelectrolyte nanocomposites with thicknesses between 1 and 10 nm. In short, a charged molecular template is deposited on a pendant drop and compressed to present a defined surface charge density to the subphase of the drop. The subphase is then cycled alternately between polyelectrolyte solutions to achieve electrostatic layer-by-layer assembly of an ultrathin nanocomposite at the drop surface. The stress response of the membrane-laden drop to dilation of its surface as measured by axisymmetric drop shape analysis is compared with a two-dimensional continuum model. The impact of surface charge density of the template and the film thickness on the two-dimensional elastic modulus, Eg, of the nanocomposite were assessed, and mechanical behavior consistent with that of an elastomeric solid is demonstrated.