Mechanical properties of nanotubes of polyelectrolyte multilayers

TL;DR

This study measures the elastic properties of polyelectrolyte multilayer nanotubes using resonant AFM, revealing lower Young's modulus values than flat multilayers due to higher water content and lower ionic cross-linking.

Contribution

It provides the first measurement of the elastic modulus of LbL polyelectrolyte nanotubes using resonant AFM, highlighting the influence of water content and growth mode.

Findings

Average Young's modulus of 115 MPa in air

Lower modulus than dry flat multilayers

Higher water content affects mechanical properties

Abstract

The elastic properties of nanotubes fabricated by layer-by-layer (LbL) assembly of polyelectrolytes in the nanopores of polycarbonate track-etched membranes have been investigated by resonant contact Atomic Force Microscopy (AFM), for nanotube diameters in the range of 100 to 200 nm. The elastic modulus of the nanotubes was computed from the resonance frequencies of a cantilever resting on freely suspended LbL nanotubes. An average value of 115MPa was found in air for Young's modulus of these nanostructures, well below the values reported for dry, flat multilayers, but in the range of values reported for water-swollen flat multilayers. These low values are most probably due to the lower degree of ionic cross-linking of LbL nanotubes and their consequently higher water content in air, resulting from the peculiar mode of growth of nanoconfined polyelectrolyte multilayers.