Special Issue Article Journal of Intelligent Material Systems and Structures 1–12 Ó The Author(s) 2015 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/1045389X15577652 jim.sagepub.com Colloidal, electrorheological, and viscoelastic properties of polypyrrole- graft-chitosan biodegradable copolymer Mehmet Cabuk 1 , Mustafa Yavuz 1 and Halil Ibrahim Unal 2 Abstract In this study, colloidal, electrorheological, and viscoelastic properties of conducting polypyrrole, biodegradable chitosan, and polypyrrole-graft-chitosan copolymer were investigated. Some physical properties such as particle size, apparent density, conductivity, magnetic susceptibility, and elemental analysis of the materials were determined. Electrokinetic properties of the materials were investigated by means of zeta (z)-potential measurements in aqueous and non-aqueous (silicone oil) media. The effects of time, pH, various electrolytes, surfactants, and temperature onto z-potentials of the dispersions prepared in aqueous media were examined. It was concluded that the positive z-potential of polypyrrole shifted to more positive regions, and the isoelectric point of the polypyrrole concomitantly shifted to higher pH values after interaction with polycationic chitosan matrix. Polypyrrole-graft-chitosan/silicone oil suspensions were observed to be electrorheological active when subjected to external electric field strength. Creep and creep–recovery tests were applied to the suspensions and a relationship was established between viscoelastic response and z-potential of the mate- rials. Furthermore, polypyrrole-graft-chitosan-based smart electrorheological fluid was observed to behave as a viscoe- lastic material and exhibited a reversible nonlinear viscoelastic deformation under externally applied electric field strength. Keywords Polypyrrole, chitosan, zeta-potential, electrorheological fluids, creep–recovery Introduction There has been considerably increasing interest on syn- thetic polymer/natural polymer hybrid materials in the past decade due to having characteristics of both syn- thetic and natural components. Chitosan (CS) is a nat- ural amino polysaccharide, which contains free amino groups (–NH 2 ) at neutral and alkaline pH values, but they are protonated (NH + 3 ) under acidic conditions, thus making ionic interactions possible upon the reac- tion with anions. In contrast to other natural polymers, CS is a hydrophilic polymer with positive charges that come from weak basic groups, which outfits it with spe- cial characteristics from the technological point of view (Dai et al., 2011; Ramaprasad et al., 2009). The primary techniques applied for modification of chemical and physical properties of CS for widening its practical use are grafting, blending, and composite for- mation, which are all multicomponent polymer systems (Aoi et al., 1997; Mourya and Inamdar, 2008). Conducting polymers having functional macromole- cules possessing conjugate p-bonds have attracted great interest for many years (Hong and Zhou, 1999). Polypyrrole (PPy) is one of the most commonly investi- gated conducting polymer due to its excellent properties such as high electrical conductivity, good environmen- tal stability, and easy synthesis (Lu et al., 2010). PPy has been known to undergo protonation or deprotona- tion process when it was immersed in basic and acidic solutions, resulting in the change in its surface charges. Among their various industrial application areas, elec- trochromic displays, biosensors, batteries, ion selective membranes, and electrorheological (ER) fluids are reported (Sahin et al., 2002; Temmel et al., 2006). 1 Department of Chemistry, Faculty of Science, Su ¨leyman Demirel University, Isparta, Turkey 2 Smart Materials Research Laboratory, Department of Chemistry, Faculty of Science, Gazi University, Ankara, Turkey Corresponding author: Mehmet Cabuk, Department of Chemistry, Faculty of Science, Su ¨leyman Demirel University, Isparta 32260, Turkey. Email: mehmetcabuk@sdu.edu.tr; mhmtcbk@gmail.com at Süleyman Demirel Üniversitesi on March 26, 2015 jim.sagepub.com Downloaded from