Effect of hydrophobicity on tensile rheological properties of silica nanoparticle monolayers at the air–water interface

We have proposed a tensile rheological study of silica nanoparticle monolayers at the air–water interface. The surface pressure of the layers exhibits significant oscillation and forms a series of sharp downward peaks in the indentation and ascending cycles of a titanium cone. The oscillation amplitude of surface pressure dΠ is resulted from the tensile deformation of the particle layer and reflects the elastic properties of the layer. The widths τdown and τup of the downward peaks are related to the relaxation time of the layer, which implies the viscosity due to the friction delay between particles. Both dΠ and τ (τdown, τup) are affected significantly by the adsorption energy of particles with the interface and depend strongly on the particle hydrophobicity. This is in line with our previous studies. The results provide deep insight into the viscoelastic behaviour of particle layer, suggesting that the proposed method has the potential for the rheological study of this kind of layers.

The particle layers deposited at the air–water interface were deformed by the indentation and ascending of a titanium cone and consequently resulted in the oscillation of surface pressure.Figure optionsDownload as PowerPoint slideHighlights
► Indentation and retraction of the cone result in tensile deformations of the particle layers.
► The amplitude of surface pressure variation and the relaxation time depend significantly on the particle hydrophobicity.
► The response of surface pressure implies the information of elasticity and viscosity.