Dynamic mechanical behavior of suspensions of fat particles in oil

Suspensions of glyceryl tristearate particles in oil are characterized by their moduli and damping at deformations between 10-5 and 10-2. The measurements have been performed at frequencies around 50 c.p.s. using two methods, one where a specimen supported by a thin metal carrier is excited into bending vibrations, and one where a torsional pendulum is used. Materials with different particle sizes have been studied; these sizes could be varied by varying the crystallization temperature. At 20°-30°C. crystallization temperature, particle sizes of 0.1 μm. and at 55°C., particle sizes of 4 μm., were obtained. For both types of suspensions, a region could be found where modulus and damping were independent of the magnitude of the deformation. At higher strains, modulus decreases and damping increases. For materials with small particles the dependence of the modulus on the solid phase concentration was studied in the region of 20% to 30% and the modulus was found to be proportional with the eighth power of the concentration of solid phase. The moduli of these suspensions are hardly dependent on the frequency in the region of 40 to 1,000 c.p.s. Kneading causes a decrease in the modulus, for suspensions with small particles about a factor of 2, for those with large particles at least a factor of 104. During storage, the modulus increases considerably; in three months time it may be increased by a factor of 5. Using a model based on van der Waals' attraction between the fat particles, some results can be explained, such as the existence of a linearity limit and the order of magnitude of the modulus. We have not yet been able to explain the relationship between modulus and concentration. © 1963.