Mechanical properties of C-60 thin films at the air-water interface

Abstract

Understanding the mechanical properties of ultra-thin films formed by the self-assembly of molecules/nanoparticles/colloids at fluid-fluid interfaces is central to many technological applications. Here, we have carried out interfacial rheology measurements to systematically investigate the concentration dependent viscoelastic response of 2D films of Fullerene C-60 at the air-water interface. With increasing C-60 concentration, amplitude sweep measurements show that the films undergo a transition from viscoelastic liquid-like to viscoelastic solid-like behaviour. Interestingly, for high C-60 concentrations's, the loss modulus G '' reaches a maximum before the onset of power-law shear-thinning in G', the storage modulus, and G ''. The power-law exponents have a ratio 2. This response is typical of systems that show soft glassy behaviour. We also observe a power-law increase in G' and G '' at low frequencies in the frequency response measurements and a transition from Newtonian to shear-thinning behaviour, with increasing shear rate, in steady shear measurements. Our results are in qualitative agreement with the phenomenological soft glassy rheology model. (C) 2015 Elsevier Ltd. All rights reserved.