Mechanical properties of plastic-disperse systems at very small deformations

Abstract A system containing flocculated solid particles in a liquid shows viscoelastic behavior at very small deformations. A model is described by means of which the elastic modulus of the system can be correlated with the forces acting between the particles. It is assumed that these forces are due to van der Waals-London attraction, and their contribution to the modulus is calculated. A method is indicated which allows the contribution of the van der Waals-London forces to the modulus of the material to be measured under specified conditions. Experiments on materials containing fat crystals in oil show agreement between predicted and experimental values for this contribution, if it is assumed that the solid particles in the aggregate approach each other to a distance of about 10 A. The energy content of the van der Waals-London bonds in these materials has been estimated from measurements of their rate of breaking in creep experiments, i.e., under the influence of a constant, low shearing stress. The energy content of about 40 kT -units is in satisfactory agreement with the results of stiffness measurements.