Development and Characterization of Hydrocarbon Polyol Polyurethane and Silicone Magnetorheological Polymeric Gels Alan Fuchs, 1 Mei Xin, 1 Faramarz Gordaninejad, 2 Xiaojie Wang, 2 Gregory H. Hitchcock, 2 Hatice Gecol, 1 Cahit Evrensel, 2 George Korol 3 1 Chemical Engineering, University of Nevada, Reno, Nevada 89557 2 Mechanical Engineering, University of Nevada, Reno, Nevada 89557 3 Visteon Automotive Systems, Dearborn, Michigan 48126 Received 3 February 2003; revised 25 May 2003; accepted 16 June 2003 ABSTRACT: Magnetorheological polymeric gels (MRPG) have been developed for use in semi-active magnetorheo- logical fluid (MRF) dampers and other magnetorheological (MR) devices. The novel MRPGs are prepared by suspend- ing iron particles in polymeric gels. Off-state (i.e, no applied magnetic field) viscosity and settling behavior can be con- trolled through the selection of polymeric gels. In this study, tunable rheological properties were investigated with a pis- ton-driven flow type rheometer with a shear rate varying from 20 s -1 to 6,000 s -1 . Silicone MRPG (with 84.5 wt % iron particles) has controllable viscosity and a high shear yield stress over a wide range of shear rates. Silicone MRPG (79.5 wt % iron particles) has the lowest viscosity of those studied. Polyurethane MRPG has the lowest settling rate. The order of addition of magnetic particles and polymer during the polymerization process affects the MRPG final off-state ap- parent viscosity (80% increase in apparent viscosity for sil- icone MRPG polymerized after adding iron particles). This indicates that polymer gels modify the surface properties of the magnetic particles, causing interaction among particles. The dynamic shear yield stress is higher for fluids with better dispersion stability. Polyurethane MRPG, which has the lowest settling rate, has a high dynamic yield stress (23 kPa at 350 mT). Both dynamic and static shear stress values of the MRPGs were found to be similar in magnitude (5– 8 kPa at 120 mT for silicone MRPG with 84.5 wt % iron particles and polyurethane MRPG), indicating that MRPGs can provide consistent performance in devices. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1176 –1182, 2004 Key words: rheology; gels; polyurethanes; silicones INTRODUCTION Magnetorheological fluids (MRFs) can respond to an externally applied magnetic field with a rapid and reversible change in their apparent viscosity. MRFs can be used in a variety of applications. These appli- cations include engine mounts, shock absorbers, clutches, and seat dampers. 1–4 Other applications are exercise equipment and aspherical optical lens polish- ing. 3 Without an applied magnetic field, a typical MRF behaves similarly to a Newtonian fluid. 1,2 When a magnetic field is applied, a dipole moment is induced within the suspended iron particles by which they align “head-to-tail” and form chains parallel to the magnetic field. 2 A MRF becomes a weak viscoelastic solid as the chains form into column-like structures when the applied magnetic field increases. As a result, the rheological properties of the material changes. 5 MRF properties are controllable because of the dra- matic change in their rheological properties under an externally applied magnetic field. Therefore, they pro- vide a new means of controlling electromechanical devices. 3 A new generation of MRFs, known as magnetorheo- logical polymer gels (MRPGs) are used in vibration control and damping devices. 6,7 These fluids have the advantage of providing controllable viscosity of the carrier fluid as well as reducing the settling of mag- netic particles in the fluid. This behavior is possible because the polymer gel distributes itself between the carrier fluid and the surface of the magnetic particles. In this respect, MRPGs are significantly different from traditional MRFs. Previous work on MRPGs 6 describes the develop- ment and characterization of poly(ethylene glycol) (PEG) and polyether polyol based polyurethanes and silicone polymer gels. These polyurethane gels are limited by their poor compatibility with hydrocarbon carrier fluids. These MRPGs were characterized using thermal analysis for determination of the kinetic be- havior of the polymer gels. MRPGs are disclosed in U.S. Patent 6,527,972. 7 These fluids contain partially crosslinked polymer gels, which are synthesized using non-stoichiometric amounts of monomers. They may include plasticizer, Correspondence to: A. Fuchs (afuchs@unr.edu). Journal of Applied Polymer Science, Vol. 92, 1176 –1182 (2004) © 2004 Wiley Periodicals, Inc.