VTT PUBLICATIONS 385 Characterization and performance of electrorheological fluids based on pine oils Kimmo K. Mäkelä VTT Manufacturing Technology Dissertation for the degree of Doctor of Technology to be presented, with the permission of the Department of Mechanical Engineering of the University of Oulu, for public discussion in Auditorium L6, Linnanmaa, on May 21st, 1999, at 12 noon. TECHNICAL RESEARCH CENTRE OF FINLAND ESPOO 1999 ISBN 951–38–5373–X (nid.) ISSN 1235–0621(nid.) ISBN 951–38–5374–8 (URL: http://www.inf.vtt.fi/pdf/) ISSN 1455–0849 (URL: http://www.inf.vtt.fi/pdf/) Copyright © Valtion teknillinen tutkimuskeskus (VTT) 1999 JULKAISIJA – UTGIVARE – PUBLISHER Valtion teknillinen tutkimuskeskus (VTT), Vuorimiehentie 5, PL 2000, 02044 VTT puh. vaihde (09) 4561, faksi (09) 456 4374 Statens tekniska forskningscentral (VTT), Bergsmansvägen 5, PB 2000, 02044 VTT tel. växel (09) 4561, fax (09) 456 4374 Technical Research Centre of Finland (VTT), Vuorimiehentie 5, P.O.Box 2000, FIN–02044 VTT, Finland phone internat. + 358 9 4561, fax + 358 9 456 4374 VTT Valmistustekniikka, Käyttötekniikka, Metallimiehenkuja 6, PL 1702, 02044 VTT puh. vaihde (09) 4561, faksi (09) 460 627 VTT Tillverkningsteknik, Driftsäkerhetsteknik, Metallmansgränden 6, PB 1702, 02044 VTT tel. växel (09) 4561, fax (09) 460 627 VTT Manufacturing Technology, Operational Reliability, Metallimiehenkuja 6, P.O.Box 1702, FIN–02044 VTT, Finland phone internat. + 358 9 4561, fax + 358 9 460 627 Technical editing Leena Ukskoski Libella Painopalvelu Oy, Espoo 1999 Mäkelä, Kimmo K. Characterization and performance of electrorheological fluids based on pine oils. Espoo 1999, Technical Research Centre of Finland, VTT Publications 385. 71 p. Keywords electrorheological fluids, rheology, pine oil, characterization, viscosity, test methods Abstract The purpose of this work is to study the characteristics and performance of pine oil and its ester as a base fluid material for electrorheological fluids. Here, all the tested fluids had a relatively low concentration level of between 5–15% of weight. As an application for rotary machines, the electrorheological strength and phenomena were studied for keeping the working fluid in a steady position while the machine is not working. The objective of this basic study is to give an introduction to the electrorheological fluids based on polyaniline particles and pine oil and to measure their dependencies on changes in the applied external electric field, temperature, shear rate, dynamic viscosity and concentration, and to study the influence of grinding the particles. Based upon the results of the investigations, the following can be concluded in the case of electrorheological fluids made of polyaniline and pine oil or its ester, treated with hexane, at temperatures between 20–60oC, shear rate 40–490 1/min, electric field strength 0.5–3.5 kV/mm: 1. An increase in electric field through the fluid increases the electrorheological strength of the fluid if the concentration level is more than 5% of weight. 2. If the fluid’s concentration is 5% of weight or less, the fluid does not express electrorheological phenomena. 3. In similar conditions, temperature has no or very little effect on the electrorheological phenomena. 3 4. The relative change in shear rate has only a small effect on the electrorheological effectiveness of the fluid if the concentration is 15% of weight or less. 5. Grinding decreases the electrorheological strength of the electrorheological fluids based on pine oils. 6. The pine oil ester is more effective as a base oil for an electrorheological fluid if the effectiveness is measured purely on the basis of maximum shear strength versus shear rate. 7. The basic idea of making an ER fluid non-hydrous and with a low concentration level was found successful, an average of over 20% increase in viscosity with a sufficient basic level of viscosity, especially if the particle concentration was 10% of weight or above and if pine oil ester was used as the carrier fluid. 4 Preface This work was carried out in the institute of Manufacturing Technology at the Technical Research Centre of Finland and in the Laboratory of Machine Design at the University of Oulu between 1996 and 1999. I would like to express my gratitude to the Ella and Georg Ehrnrooth Foundation and to the Tekniikan Edistämissäätiö for their financial support and to VTT Manufacturing Technology for the authorization to do this work. Professor Tatu Leinonen has given me great help in my studies and by supervising this thesis. I would like to express my sincere thanks to Professor Kenneth Holmberg of VTT Manufacturing Technology for his guidance in my work with this thesis and for the excellent post-graduate school within VTT Manufacturing Technology´s Operational Reliability Laboratory, which gave me the opportunity and time to do this thesis. I would also like to thank Mr. Jorma Niskala and Mr. Ari Saastamoinen for the materials and support needed for this work, and Jouni Enqvist Ph.D. and Ms. Maija Parsio from VTT Chemical Technology for making the ER fluids. Last but not the least, I would like to thank the personnel of my laboratory, especially Mr. Matti Säynätjoki and Mrs. Helena Ronkainen, for their co-operation and help with my studies and testing. Otaniemi, 18 March, 1999 Kimmo K. Mäkelä 5 Contents Abstract............................................................................................................................ 3 Preface.............................................................................................................................. 5 List of symbols .................................................................................................................8 1. Introduction ............................................................................................................ 9 2. Electrorheological fluids ...................................................................................... 14 2.1 Electrorheological phenomena ........................................................................... 14 2.2 Rheology ............................................................................................................ 15 2.3 The rheology of electrorheological fluids........................................................... 16 2.4 Electrorheological fluids .................................................................................... 21 2.4.1 Particles ............................................................................................................ 22 2.4.2 Carrier fluids..................................................................................................... 26 2.4.3 Surfactants......................................................................................................... 27 2.4.4 Additives............................................................................................................ 28 2.4.5 ER-MR and ER-MF fluids................................................................................. 30 3. Test methods.......................................................................................................... 31 3.1 Materials............................................................................................................. 31 3.1.1 Polyaniline................................................................................................. 34 3.1.2 The preparation of ground particles ......................................................... 35 3.1.3 Fatty acid and ester carriers ..................................................................... 37 3.1.4 Paraffinic oil carrier ................................................................................. 37 3.2 Experimental arrangement.................................................................................. 38 4. Results.................................................................................................................... 41 4.1 Experimental parameters.................................................................................... 41 4.2 Influence of shear rate ........................................................................................ 42 4.3 Influence of applied external electric field ......................................................... 44 4.4 Influence of temperature..................................................................................... 45 4.5 Influence of particle size and grinding ............................................................... 48 5. Discussion .............................................................................................................. 50 6. Summary and conclusions.................................................................................... 54 References ......................................................................................................................57 6 List of symbols a Average radius of the particle A Effective area D Average distance between the centres of two particles E Electric field f Friction force fd Dipole force between polarized particles FForce Fp Axial force between the particles h Film thickness k Boltzmann constant Kf Relative permittivity of the carrier liquid Kp Relative permittivity of the particle Mn Mason number N Number of contacts between particles in the whole system n Power-law index n p Number of contacts per particle NA Number of chains per unit area p Dipole moment between particles T Temperature in Kelvin u Velocity Wsep Force needed