Silica nanoparticle suspensions under confinement of thin liquid films.

The paper deals with the effect of geometrical confinement on the structuring of Silica nanoparticle suspensions in thin films. The confinement is produced by a Colloidal Probe AFM. Approaching of the two outer surface leads to oscillatory forces. The force profile reflects the pair correlation function and its period the average distance between the nanoparticles under confinement. The nanoparticle structuring is compared to the particle distribution in bulk by small angle X-ray scattering (SAXS). The SAXS structure factor which presents the Fourier transform of the pair correlation function gives the same interparticle distance for the bulk as the oscillation period of the AFM force curves. The distance scales with particle number density ρ as ρ(-1/3) and is very robust against different suspension parameters (nanoparticle size, ionic strength) and parameters of the outer surfaces (surface potential, roughness and elasticity).