Synthesis of imidazolium salts and their application in epoxy montmorillonite nanocomposites J. Langat a , S. Bellayer b,1 , P. Hudrlik a , A. Hudrlik a , P.H. Maupin c , J.W. Gilman Sr. b , D. Raghavan a, * a Department of Chemistry, Howard University, 525 College Street, NW, Washington, DC 20059, USA b Fire Research Division, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA c Office of Basic Energy Science, Office of Science, U.S. Department of Energy, Washington, DC 20585, USA Received 10 February 2006; received in revised form 27 June 2006; accepted 28 June 2006 Available online 9 August 2006 Abstract Considerable research has been conducted in improving the performance characteristics of nanocomposites, however, relatively few attempts have been made to address the thermal stability of nanocomposites. An attempt is being made to improve the thermal properties of nanocompo- sites by synthesizing imidazolium salts from 2-methyl imidazole and ion exchanging the salts with clay minerals. This study focuses on the role of the chemistry of imidazolium salt(s) used in functionalizing clay and processing conditions in the formulation of epoxy nanocomposites. The nanodispersion of clay in an epoxy matrix is evaluated qualitatively by X-ray diffraction (XRD), transmission electronic microscopy (TEM), and laser scanning confocal microscopy (LSCM). We demonstrate the use of LCSM for quantitative image analysis and to study the dispersion of clay layers, tagged with a fluorescent dye in the epoxy matrix. XRD and TEM results reveal that the hand mixed nanocomposite has tactoid morphology, while ultrasonicated organoclay (without hydroxyl group) epoxy nanocomposite exhibits a mixed morphology, and an ultrasonicated organoclay (with hydroxyl group) epoxy nanocomposite had well dispersed clay distribution in the epoxy matrix. Results from the three compli- mentary techniques enable the characterization of the clay platelets over several length scales ranging from the micrometer to the nanometer scale. Ó 2006 Elsevier Ltd. All rights reserved. Keywords: Clay nanocomposites; Thermal stability; Confocal microscopy 1. Introduction During the last decade, the area of nanoclay filled polymers has received much attention from both the scientific and tech- nological communities with the expectation that the materials designed will be lighter and more superior to the pristine poly- mers. In particular, the attractiveness of polymereclay nano- composites resides in the potential of adding small amounts of clay platelets to polymeric resin, to dramatically improve mechanical, thermal, barrier, and flame-retardant properties [1e10]. Because of the potential benefits of adding inexpensive clay filler to the polymer matrix, the automotive and aerospace industries view polymereclay hybrid nanocomposites as prom- ising structural materials for the 21st century [11]. Considerable research has been conducted to study the structureeproperty relationship of organically modified claye epoxy nanocomposites [12e18]. Tsai and Sun [19] modeled the load transfer efficiency in nanocomposites and noted that significant enhancement in reinforcement can be achieved by having the clay platelets well dispersed in the polymer matrix. By ion exchanging Na þ , Ca 2þ , or K þ on the clay surface with a long chain cation, attempts have been made to disperse lay- ered particles (hydrophilic) in polymer matrix (hydrophobic). Typically nanoclays treated with alkyl ammonium ions have been used to produce clayeepoxy nanocomposites. The archi- tecture of the alkyl ammonium ion has been commonly chosen * Corresponding author. Tel.: þ1 202 806 4427; fax: þ1 202 806 5442. E-mail address: draghavan@howard.edu (D. Raghavan). 1 Guest Researcher from France. 0032-3861/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2006.06.067 Polymer 47 (2006) 6698e6709 www.elsevier.com/locate/polymer