Nonlinear viscoelastic behavior of aqueous foam under large amplitude oscillatory shear flow

Abstract

Aqueous foams are dispersions of gas bubbles in water, stabilized by surfactant, and sometimes particles. This multiphasic composition gives rise to complex rheological behavior under deformation. Understanding this behavior is important in many applications. Foam shows nonlinear rheological behavior at high deformation, which can be investigated by the large amplitude oscillatory shear (LAOS) experiments. In the present work, we have performed a systematic LAOS study of foam stabilized by 0.1 mol m−3 hexadecyltrimethylammonium bromide and 0.5 wt.% silica nanoparticles. The Lissajous-Bowditch curves and stress waveforms were analyzed at various strain amplitudes. These curves were fitted by Fourier transform rheology and Chebyshev polynomials to understand the contribution of the higher harmonic terms in LAOS. The intracycle LAOS behavior was explained based on the sequence of physical processes. The foam exhibited intracycle strain-hardening and shear-thinning at high deformation. Shear-thickening behavior was observed at moderate deformations.