Attaining a controlled graded distribution of particles in polymerizing fluid for functionally graded materials

Abstract

The precise control on concentration profile of dispersion in functionally graded material (FGM) is essential for obtaining a desired material. A suitable simulation of parameters and an appropriate model that describes the motion of particles in the fluid can predict various aspects those are needed to produce FGM, by gravity sedimentation or centrifugation technique. Simulation was conducted to observe the changes in concentration profile, while using the following equations applicable to polymerizing fluid, and to determine the terminal velocities (Vm) of particles; Vm = {D 2(ρs - ρl)g*(1 - Φ s)4.65}/(18μ0ebtc) for gravity sedimentation and Vm = {D2(ρs - ρ l,)rω2(1 -Φs) 4.65}/(18μ0 ebtc) for centrifugation, where D is the diameter of the spherical particle, ρs the density of solid particles, ρl the density of fluid, μ the viscosity of fluid, g* the acceleration due to gravity, Φs is the volume fraction of particles, and tc is the elapsed time of curing of thermosetting resin, b is a constant, r is the radius, and ω is the angular velocity. This simulation demonstrates that the time of centrifugation/sedimentation, particle size, distribution of particle size, and centrifugal/gravitational forces can be effectively utilized to attain a desired concentration profile in graded materials. Simulation also revealed that there exist the possibility of two graded profiles, namely low concentration profile and high concentration profile, in one sample of graded material, made either by centrifugation or sedimentation. Low concentration profile is more sensitive to particle size distribution as compared to high concentration profile. The present simulation method is also sensitive to concentration-measuring methods. © 2006 Wiley Periodicals, Inc.