Nonlinear Viscoelastic Properties of Semisolid Emulsions

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Abstract
The dynamic viscoelasticproperties of semisolid emulsions (commercial cosmetic creams) at 25°C were measured by means of a Weissenberg rheogoniometer at frequencies ranging from 1.582×10 −3 to 1.582 Hz. In general, these emulsions manifested remarkable nonlinear viscoelasticity even at very small strains; when sinusoidal strains were applied to the emulsions, the resultant stresses were not sinusoidal, in marked contrast to the case in ordinary linear viscoelasticmaterials. Such nonsinusoidal stresses were analyzed by the method proposed by Onogi et al. to give nonlinear viscoelastic functions. The frequency dependences of these nonlinear functions for the emulsions were quite different from those of the viscoelastic functions for polymer solutions or melts, especially in the low frequency range; the viscoelastic functions for the semisolid emulsions showed second plateaus lower than the so‐called rubbery plateau. Some considerations concerning the origin of the nonsinusoidal stresses were given, and it was concluded that the origin was the dynamic yield stress which was originated from the structure in the semisolid emulsions.

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