Macromolecular Nanotechnology Effect of montmorillonite on gelation and swelling behavior of sulfonated polyacrylamide nanocomposite hydrogels in electrolyte solutions Jamal Aalaie a , Ebrahim Vasheghani-Farahani a, * , Ali Rahmatpour b , Mohammad Ali Semsarzadeh a a Chemical Engineering Department, Tarbiat Modares University, Jalal Al Ahmad Highway, P.O. Box 14155-143, Tehran, Iran b Polymer Science and Technology Division, Research Institute of Petroleum Industry (RIPI), P.O. Box 18745-4163, Tehran, Iran article info Article history: Received 19 November 2007 Received in revised form 17 February 2008 Accepted 18 April 2008 Available online 29 April 2008 Keywords: Nanocomposite Hydrogel Sulfonated polyacrylamide Swelling Electrolyte solutions Enhanced oil recovery abstract Nanocomposite hydrogels were prepared by cross-linking of aqueous solutions of sulfo- nated polyacrylamide/sodium montmorillonite with chromium triacetate. The gelation process and effects of clay content and ionic strength on swelling behavior were investi- gated. X-ray diffraction patterns indicated that exfoliated type of microstructure was formed. Study of the gelation behavior using dynamic rheometery showed that the limiting storage modulus of the nanocomposite (NC) gels decreased with increasing clay content up to 1000 ppm, but it increased by further increase of Na + -montmorillonite concentration. It was also found that with increasing the clay content, the viscous energy dissipation prop- erties of the nanocomposite gels increased. The swelling ratio of nanocomposite gels in tap water decreased as the concentration of the clay increased. However, nanocomposite gels showed higher resistance against syneresis in electrolyte solutions as compared with unfilled gels. Therefore, they are potentially good candidates for enhanced oil recovery applications. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Hydrophilic cross-linked polymer networks, i.e., hydro- gels, are capable of absorbing and retaining large quanti- ties of water. Because of their unique characteristics like hydrophilicity, swelling in aqueous media, and non-soluble nature in aqueous fluids, they are widely used in many applications such as hygiene, cosmetics, agriculture, medi- cine, biotechnology, and petroleum recovery treatments of mature reservoirs [1–5]. It has been found that increasing cross-linker concentration can enhance mechanical strength of hydrogels. However, a large amount of cross- linker could result in the reduction of swelling capability and mechanical toughness [6,7]. Recently, to overcome the weakness and limitations of the conventional hydro- gels, preparation of nanocomposite hydrogels have at- tracted more attention [8–14]. These nanocomposite (NC) hydrogels have excellent properties, such as mechanical toughness, large deformability, high swelling/deswelling rates, and high transparency. These remarkable improve- ments in properties of nanocomposite hydrogels were as- cribed to their characteristic network structure [9,15]. On the basis of the results of mechanical and swelling/ deswelling properties of NC hydrogels, Haraguchi and Takehisa [11] proposed the existence of a unique organic/ inorganic network structure for poly (N-isopropylamide) (PNIPA) – clay NC hydrogels. Their model is based on a uni- form dispersion of exfoliated inorganic clay in an aqueous medium and PNIPA chains grafted on the clay surface at one or both ends. These NC gels mainly consist of polymer chains connecting neighboring clay sheets. In other words, polymer chains are effectively cross-linked by clay sheets. Also, because of the large distance between the clay sheets, 0014-3057/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.eurpolymj.2008.04.031 * Corresponding author. Tel.: +98 21 88011001; fax: +98 21 88005040. E-mail address: evf@modares.ac.ir (E. Vasheghani-Farahani). European Polymer Journal 44 (2008) 2024–2031 Contents lists available at ScienceDirect European Polymer Journal journal homepage: www.elsevier.com/locate/europolj MACROMOLECULAR NANOTECHNOLOGY