The pillaring effect of the 1,2-dimethyl-3(benzyl ethyl iso-butyl POSS) imidazolium cation in polymer/montmorillonite nanocomposites Douglas M. Fox a, b, * ,1 , Richard H. Harris Jr. b , Severine Bellayer b,1 , Jeffrey W. Gilman h, ** , Mikhail Y. Gelfer c, d , Benjamin S. Hsaio c, d , Paul H. Maupin b, e, 1 , Paul C. Trulove f , Hugh C. De Long g a Department of Chemistry, American University, Washington, DC 20016, USA b Fire Research Division, Engineering Laboratory, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA c Department of Chemistry, State University of New York at Stony Brook, Stony Brook, NY 11794, USA d National Synchrotron Light Source, Brookhaven National Laboratory, Upton, NY 11973, USA e Office of Basic Energy Sciences, Office of Sciences, U.S. Department of Energy, Washington, DC 20585, USA f Chemistry Department, U. S. Naval Academy, Annapolis, MD 21402, USA g Mathematics, Information, and Life Sciences Directorate, Air Force Office of Scientific Research, Arlington, VA 22203, USA h Polymers Division, Material Measurement Laboratory, National Institute of Standards and Technology, Gaitherburg, MD 20899, USA article info Article history: Received 1 July 2011 Received in revised form 4 September 2011 Accepted 10 September 2011 Available online 16 September 2011 Keywords: POSS Montmorillonite Nanocomposites abstract A polyhedral oligomeric silsesquioxane (POSS) tethered imidazolium surfactant was used to exchange montmorillonite for the preparation of polymer nanocomposites in polystyrene, poly(ethylene-co-vinyl acetate), and polyamide-6 using a melt blending technique. Simultaneous temperature resolved small angle X-ray scattering and wide angle X-ray diffraction was used to monitor the surfactant stability and phase behavior of the polyamide-6 nanocomposites. Good thermal stability of the surfactant was in agreement with thermogravimetric analysis. Transmission electron microscopy revealed a mixed inter- calated/exfoliated structure, with the presence of small tactoids exhibiting gallery spacings greater than 3.8 nm in all three polymers. Fluorescently tagged organically exchanged montomorillonite was used to assess the quality of nanoparticle dispersion. Exchanging the montmorillonite with lower loadings of the POSS surfactant slightly increased the size of clay tactoids, but did not significantly alter the gallery spacing or overall dispersion. The results suggest that the bulky and rigid structure of POSS, as well as its tendency to aggregate into ordered crystals, form a bilayer structure in the clay galleries and prevent montmorillonite from completely exfoliating, even in polyamide-6. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction The addition of silicates and other silicon oxide species to polymers has been shown to significantly improve many desirable properties, including thermal stability, flammability, mechanical strength, and barrier properties [1e 11]. Much of their value lies in their ability to improve polymer performance at relatively low loadings. Layered silicates [1e6] and polyhedral oligomeric silses- quioxanes [10e12] are two such additives that have shown great promise for commercial applications. Polymer e layered silicate nanocomposites (PLSNs) have been extensively studied for over twenty years. They have shown promise for the manufacture of low-cost, light-weight, and high- performance nanocomposites and have even found use in some commercial applications [4,5]. The addition of these materials to polymers have often resulted in reduced flammability, especially when combined with other flame retardants [6,13,14]. However, the high processing temperature of some polymers, such as polyamides or polycarbonate, typically result in the degradation of commonly used organic surfactants, such as alkylammonium cations. To improve the thermal stability of the organically modified layered silicates during processing, imidazolium based ionic liquids have been used as the organic modifiers [15e19]. The incorporation of polyhedral oligomeric silsesquioxane (POSS) into polymers has also received much attention in recent years [20e27]. Unlike traditional organic compounds, most POSS compounds release no volatile organic compounds below 300  C, * Corresponding author. Department of Chemistry, American University, Washington, DC 20016, USA. ** Corresponding author. E-mail addresses: dfox@american.edu (D.M. Fox), jeffrey.gilman@nist.gov (J.W. Gilman). 1 Guest Researcher. Contents lists available at SciVerse ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer 0032-3861/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2011.09.016 Polymer 52 (2011) 5335e5343