COATED GLASS MICROSPHERES IN ERF APPLICATIONS

ER fluids (ERFs) typically consist of a concentrated dispersion of solid particles in a nonconducting base fluid. As a result, particle sedimentation represents a significant problem for many formulations since, in most cases, the particulate phase is of higher density than the base fluid. To remedy this situation, higher density fluids have been widely used in ERFs (ρ > 1.1 g / cc) rather than less expensive mineral oils that display lower densities (0.8 - 0.9 g / cc). An alternative approach to density "matching" has been explored by Qi and Shaw who have successfully developed ERF particles based on low density, micron-sized hollow glass "balloons" that are polymer coated. These microballons are commercially available from the PQ Corporation and they exhibit an effective density of 0.7 g / cc. Using these materials, it becomes possible to engineer ERF particles that are "neutrally buoyant" in mineral oils by adjusting the coating weight of an ER active polymer on the glass spheres.

In this study, a simple solution coating process was developed exploiting the unique surface chemistry of glass which contains -Si-O-Si- and -Si-OH sites capable of hydrogen bonding with hydrophillic polymers. A number of water-soluble ionic polysaccharides were evaluated as coatings because of their ability to form hydrogen bonds with glass surfaces. A synthetic alcohol-soluble polymer, sulfonated polyphenylene oxide, was also evaluated because of its thermal stability and mechanical durability.