Dynamic rheological properties of highly concentrated protein-stabilized emulsions

We have measured the dynamic rheological properties of highly concentrated emulsions of soya oil in water, stabilized with sodium caseinate, as a func tion of oil phase volume fraction (phi greater than or equal to 0.70). Expe riments were carried out in oscillatory mode on a controlled stress rheomet er, as a function of applied stress and frequency. At low stresses these em ulsions behave as a gel whose elastic properties, as a function of phi, fol low the empirical model of Princen (J. Colloid Interface Sci. 1986, 112, 42 7) and are controlled by the Laplace pressure of the oil droplets. At highe r stresses, the frequency spectra show a Maxwellian behavior with a single relaxation time. The frequency sweeps can be superimposed at each phi value onto a single master curve scaled against their Maxwellian relaxation time . Strain sweeps, derived from the frequency spectra at these higher stresse s are also superimposable using as scaling factor the ratio, reference stre ss to the applied stress. A frequency-dependent yield stress is also observ ed, the response varying with the oil volume fraction.