Nonlinear viscoelasticity, percolation and particles dispersibility of PVA/aluminum hydroxide composite gels

We investigated the rheological properties of a composite gel consisting of poly(vinyl alcohol) and aluminum hydroxide particles, and discussed the relation among nonlinear viscoelasticity, percolation and particles dispersibility. The dynamic viscoelastic measurements revealed that the storage modulus at volume fractions ϕ < 0.04 satisfied with the Krieger–Dougherty equation representing random dispersion of particles. The storage modulus did not show any nonlinear viscoelastic response at ϕ < 0.04. However, the storage modulus at ϕ > 0.06 took a value which is far larger than that expected by the equation, indicating heterogeneous distribution of particles. Additionally, the nonlinear viscoelastic response was recognized clearly at ϕ > 0.06, suggesting a partial contact between particles. The storage modulus at ϕ > 0.18 showed a further increase satisfied with the percolation theory, therefore, the volume fraction is considered to be the percolation threshold of 3-dimension. Microscopic observations of the gel showed a clear network with a mesh size of few μm that is considered to be a partial network of particles.