Effects of Dispersant Molecular Structure on the Stabilization of Dispersions Against Agglomeration and Sedimentation

Purdue University, West Lafayette IN

Investigators

Abstract

Many industrially important processes involve suspensions of particles in a liquid. These processes are often hampered by agglomeration of the particles and sedimentation of the aggregates. Process engineers take steps to prevent agglomeration and sedimentation by adding surfactants, compounds that lower the surface tension between two liquids or between a liquid and a solid, that coat the particles and inhibit their agglomeration. However, adding a surfactant can also change the bulk properties of the suspension and make it more difficult to process. This research project involves studying and alternative approach to preventing agglomeration and sedimentation without changing significantly the flow properties of the suspension. The idea is to find surfactants that spontaneously form molecular structures or assemblies in the liquid that prevent particle agglomeration, sedimentation, or both. The researchers are examining a broad array of surfactant-particle systems and determining the characteristics of the system that prevent agglomeration. The results will help enable process engineers in such industrial areas as paints and inks, pharmaceuticals, and cosmetics to design products that remain stable and maintain their beneficial properties over long periods of time. The project also involves students at all academic levels, including high school students, especially those from traditionally underrepresented groups, who are being recruited to participate in the project through Purdue's SEED program. The goal of this project is to screen, evaluate, and select surfactant dispersants for controlling agglomeration and sedimentation of suspended particles. The role of surfactant molecular structure on the formation of assemblies such as micelles and vesicles that can inhibit agglomeration and sedimentation of particles is being investigated. A broad array of surfactants are being examined including single and double hydrocarbon chains connected to single and double polar head groups. Anionic, cationic, and nonionic surfactants with carbon chain lengths from 8 to 16 are being studied. Characteristics of the particles, such as size, composition, density and concentration, is also being included in the study. Agglomerate size is being determined by dynamic light scattering and spectroturbidimetry, and changes in rheological properties are being measured using a constant stress rheometer. Cryo-transmission electron microscopy is being used when appropriate to characterize vesicle and particle structures. Computational studies using Brownian Dynamics and Stochastic Dynamics simulations are being carried out to identify mechanisms of suspension stabilization.