Effect of hydrophobicity on the interfacial rheological behaviors of nanoparticles at decane-water interface

Abstract

In order to elucidate the structure-property relationship of nanoparticle film, the behaviors of silica nanoparticles at water-decane interface have been detected by dynamic interfacial tension and interfacial dilational rheological measurements. Three silica nanoparticles with the similar size but different hydrophobic surfaces have been employed and the influences of bulk concentration have been investigated. Experimental results show that hydrophobically modified nanoparticles will adsorb at the interface to reduce interfacial tension. The interfacial tension becomes lower with the increase of hydrophobicity of nanoparticle at the same bulk concentration. The obvious dynamic behaviors appear and the variations of moduli with droplet aging time become irregular before equilibrium for two hydrophobic nanoparticles when the bulk concentrations are higher that a certain value. This indicates the repeated construction and destruction of the aggregates induced by oscillating droplet at the interface before the formation of equilibrium solid multilayer. The elastic, solid-like network structures are formed by hydrophobic nanoparticles at the interface, which can be proved by the nonlinear response of interfacial tension to the oscillating area. Moreover, the solid-like film shows higher modulus with the increase of hydrophobicity of nanoparticle due to the enhancement of interfacial interactions.