Comparison of the Mechanical Properties of Self-Assembled Langmuir Monolayers of Nanoparticles and Phospholipids

TL;DR

This study compares the mechanical properties of self-assembled monolayers of nanoparticles and phospholipids, revealing similarities in compressive stiffness but differences in shear response and the influence of particle size distribution.

Contribution

It provides the first direct comparison of the anisotropic mechanical properties of nanoparticle and lipid monolayers, highlighting the effect of nanoparticle polydispersity.

Findings

Nanoparticle and lipid films have similar compressive moduli.

Lipid films exhibit significantly lower shear moduli.

Broader nanoparticle size distribution reduces film stiffness.

Abstract

Nanoparticles with hydrophobic capping ligands and amphiphilic phospholipids are both found to self-assemble into monolayer films when deposited on the air water interface. By separately measuring the anisotropic stress response of these films under uniaxial compression, we obtain both the 2D compressive and shear moduli of a range of different thin nanoparticle and phospholipid films. The compressive moduli of both nanoparticle and lipid films in the solid phase are on the same order of magnitude, whereas the shear moduli of the lipid films are found to be significantly lower. Additionally the moduli of the nanoparticle films depended substantially on the polydispersity of the constituent particles: broader size distribution lowered the stiffness of the nanoparticle film.