Random packing of polydisperse spheres as a model of shrunken solidified suspensions

We propose a process-based model of shrunken solidified suspensions that are formed, for example, as a result of evaporation of a volatile solvent from a liquid polymer matrix. The suspension shrinks in the vertical direction, which is accompanied by the collective vertical movement of the thickening matrix and filler particles. We assume that the displacement of each volume element of the liquid mixture is directly proportional to the initial distance from the bottom of the casting container. If a particle collides with particles at lower positions, all the lower particles will recursively move downwards. If this is not possible, the rules for sequential ballistic deposition of particles are used. Microstructural properties of the resulting packings are studied in the particle volume fraction interval [0.05,0.38] and for a log-normal distribution of sphere sizes. Since the rigid matrix provides mechanical stability to particle clusters, sample-spanning clusters form at relatively low values of the particle volume fraction, namely between 0.28 and 0.32. All packings are nearly statistically homogeneous. The formation of large particle clusters connecting the opposite sides of the simulation box thus confirms the results extracted from 3D images of relatively small sections of real material obtained using the FIB-SEM method.