Shell-to-core ratio dependence on modulating interactions between core-shell composite nanoparticles at an air-aqueous interface

Abstract

The current study examined the shell-to-core ratio (λ) dependence on modulating interactions between core-shell composite particles (CPs) at the air-aqueous interface. The CPs were prepared by physical adsorption of poly(vinylpyrrolidone) (PVP) on the surface of silica nanoparticles (NPs). The λ value increases with increasing PVP adsorption density and PVP molecular weight. The resulting CPs are referred to as CPs8, CPs40, CPs360, and CPs1300 respectively, depending on the molecular weight of PVP that being used. The 8 kDa PVP shell is thin, and the CPs8 behave more like hard spheres at the interface. Hence, great shear and compressional elasticities of the CPs8-laden interface were measured. Whereas, higher values of λ (thicker PVP shells) induce a stronger steric barrier, which dominates the self-assembly of the CPs and modulates the microstructure of the CPs-laden interface into more complex and non-hexagonal phases (i.e. anisotropic chains), e.g. for the CPs360 and CPs1300 cases. The enhanced steric repulsion between the polymer shells makes significant contributions in building up the surface pressure before the solid particle cores being sufficiently compressed, which reduces the apparent particle surface coverage, lubricates the CPs-CPs interaction, and facilitates the rearrangement of the CPs under compression and shear, resulting in interfacial films with weak viscoelasticity. The CPs40, however, showed a transition behavior between the “hard” CPs8 and the “softer” CPs360 and CPs1300 at the air-aqueous interface.