Abstract
Nanoparticles significantly alter the rheological properties of a polymer or monomeric resin with major effect on the further processing of the materials. In this matter, especially the influence of particle material and disperse properties on the viscosity is not yet understood fully, but can only be modelled to some extent empirically after extensive experimental effort. In this paper, a numerical study on an uncured monomeric epoxy resin, which is filled with boehmite nanoparticles, is presented to elucidate the working principles, which govern the rheological behavior of nanoparticulate suspensions and to simulate the suspension viscosity based on assessable material and system properties. To account for the effect of particle surface forces and hydrodynamic interactions on the rheological behavior, a resolved CFD is coupled with DEM. It can be shown that the particle interactions caused by surface forces induce velocity differences between the particles and their surrounding fluid, which result in increased drag forces and cause the additional energy dissipation during shearing. The paper points out the limits of the used simulation method and presents a correction technique with respect to the Péclet number, which broadens the range of applicability. Valuable information is gained for a future mechanistic modelling of nanoparticulate suspension viscosity by elucidating the interdependency between surface forces, shear rate and resulting drag forces on the particles.
Highlights
Numerous reports exist on the strong effect of nanoparticles on the rheological behavior of nanoparticulate suspensions [1]
This proves the significance of surface forces for the rheological behavior of nanoparticulate suspensions
Even without surface forces, the simulated viscosity is slightly larger than Einstein’s prediction, because the dilute limit of 2 vol.% [44] is exceeded and hydrodynamic interactions lead to additional energy dissipation
Summary
Numerous reports exist on the strong effect of nanoparticles on the rheological behavior of nanoparticulate suspensions [1]. Surface forces are considered to be the dominating cause of the strong observable increases in viscosity [2,3]. Despite extensive and persistent effort of the scientific community to develop methods and models to predict the rheological properties of suspensions [5], the range of applicability of such methods and models is still very limited [6,7]. This particular work is done in the focus of the production of lightweight fiber reinforced nano-composite structures for aerospace applications. The key obstacle in this field is the fact that the beneficial effect on the mechanical properties comes with the disadvantage of a steep increase in viscosity, which has a strong effect on the processing [8,9]
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