Multilayered polymeric nanotube bending elasticity from optical-tweezers micromechanics

Abstract

We measure the bending deformation of SMA/PEI polymer multilayered nanotubes induced by a transverse hydrodynamic flow past optically trapped nanotube-micro-sphere assemblies in overhanging and end-supported beam configurations. Theoretical analysis of the deformation furnishes the bending stiffness and elastic modulus, the latter of which we compare to values from dry “nanopaper” sheets and other polymer multilayer systems reported in the literature. The results suggest that covalent cross-linking between the SMA and PEI layers produces stiff, water-stable laminates, whereas neither component forms a stable solid in water on its own. The proof of principle for optical-tweezers micromechanics demonstrated here furnishes a persistence length EI/(k_BT) ∼ 10 m with elastic modulus E ∼ 1 GPa. Further quantitative refinements of the technique may lead to a robust material characterization for similarly dimensioned soft nano-particulates. The multilayered nanotubes in this study have a higher elastic modulus than generally achieved with polyelectrolyte multilayers, and the mechanical properties are qualitatively consistent with predictions of macro-scale continuum theory.