Linear viscoelastic properties of adhesive soft particle glasses

Abstract

A model is presented to predict the linear viscoelastic rheology of hydrophobically modified adhesive soft particle glasses in an aqueous solution. The hydrophobes on the surfaces of particles in contact preferentially associate with each other, creating an adhesive force between particles. The extent of this adhesive force depends on the number of associating or physically bonded hydrophobes and the strain on the bonds. The model is first presented for two horizontal surfaces with hydrophobes attached to them. The force required for oscillatory movement between these adhesive surfaces exhibits a Maxwellian behavior with a single relaxation time that is about the time for hydrophobe dissociation. The model is extended to predict the storage and loss moduli of adhesive soft particle glasses in ordered cubic lattices. In addition to the adhesive force, the particles also exhibit repulsive elastic and elastohydrodynamic interparticle forces. For situations where there is no adhesive force between particles, the storage modulus is independent of frequency, and the loss modulus is a linear function of frequency. The storage and loss moduli as functions of frequency are richer with adhesive forces. The storage modulus exhibits two plateaus, one at low and one at high frequency. The loss modulus exhibits a local maximum in frequency that occurs at approximately the dissociation rate of the hydrophobes.