  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.
