Photoluminescence of Epoxy/Clay Nanocomposites Margarita Mondrago ´ n, 1 Miguel Angel Cortes, 1 Eduardo Arias, 2 Ciro Falcony, 3 Orlando Zelaya-Angel 3 1 Instituto Polite ´ cnico Nacional, ESIME Azcapotzalco, Av de las Granjas 682, 02250 Me ´ xico, D.F. Me ´ xico 2 Centro de Investigacio ´n en Quı´mica Aplicada, CIQA, Boulevard Enrique Reyna 140, 25253 Saltillo, Coahuilla, Me ´ xico 3 Centro de Investigacio ´n y de Estudios Avanzados del IPN, Departamento de Fı´sica, Apdo. Postal 14-740, Me ´ xico, D.F. Me ´ xico Polymer nanocomposites of an epoxy resin with natu- ral montmorillonite (MMT), organically modified mont- morillonite(OMMT), and halloysite nanotubes(HNTs) were prepared by the solvent casting method. Photolu- minescence (PL) measurements showed that the epoxy nanocomposites with OMMT and HNTs give rise to a red-shift of the emission band associated to bisphenol groups and to well resolved emission spectra, attribut- able to coplanar packing of the polymer chains in the excited states. A significant PL quenching in all the nanocomposites was observed, which depended on type and clay concentration. Atomic force microscopy (AFM) images showed a greater penetration of the ep- oxy resin only into the OMMT and HNT agglomerates. A relationship between the PL behavior and both the extent of confinement of polymer chains in clays agglomerates and the changes in the formation of trapping sites produced from hydroxyl groups could be revealed by AFM images and Fourier transform infrared spectroscopy (FTIR) studies. POLYM. ENG. SCI., 51:1808– 1814, 2011. ª 2011 Society of Plastics Engineers INTRODUCTION The most widely used plastic scintillators are based on polystyrene with added fluorescent dye molecules. How- ever, it has been shown that scintillators based on other polymers exhibit several advantages [1, 2]. In particular, epoxy systems are easy to shrink very little during poly- merization. Recently, transparent polymer nanocomposites films with low coefficient of thermal expansion have been pre- pared using clays [3, 4]. Both properties are relevant to plastic scintillators. On the other hand, to optimize the energy transfer process between the host and the dopants, the polymer fluorescence spectrum must overlap as well as possible with the dye absorption spectrum. Albeit the dielectric properties of epoxy/montmorillonite-clay nano- composites have proven to be affected by the nanostructu- ration imposed by the interactions among their compo- nents, little attention has been paid up to now to the analysis of the photoluminescence (PL) in these nanocom- posites [5]. Montmorillonite (MMT) is a clay mineral often used due to the special interlayer structure of its stacked silicate sheets (thickness 1 nm, length 130–180 nm), which chemical formula is M þ y (Al 2-y Mg y )(Si 4 )O 10 (OH) 2 .nH 2 O [6]. When nanoscale dispersion of this layered clay is achieved, intercalated and/or exfoliated structures are usu- ally observed. In the intercalated form, polymer chains are introduced between the layers that retain their ordered mul- tilayer morphology. In the exfoliated form, the silicate layers are fully delaminated and individually dispersed in the polymer matrix [7, 8]. Ion exchange of the Na þ and Ca 2þ gallery cations in the natural MMT by alkylammo- nium and alkylphosphonium ions may facilitate intercala- tion of the polymer and exfoliation of the silicate layers by lowering their surface energy and improving their wettabil- ity by hydrophilic polymers, or by increasing the gallery spacing. These clays are further called organoclays (OMMT) [9]. Recently, several papers have been published on the optical and electronic properties of conjugated polymer/ MMT-clay nanocomposites [10–12]. Nanoscale architec- ture has been used to control the physical conformation of the polymer chains and the way the chains pack to- gether, which in turn affect the luminescent efficiency and the energy transfer in conjugated polymer [13, 14]. Spe- cifically, the red-shift or blue-shift of the PL spectra of the poly[2-methoxy-5-(2 0 -ethyl-hexyloxy)-1,4-phenylene- vinylene] (MEH-PPV) loaded with organoclays was attributed to changes of chain conformation from compact coil to extended coil or vice versa, respectively [15, 16]. Correspondence to: Dr. Margarita Mondrago ´n; e-mail: mmondragon@ipn.mx DOI 10.1002/pen.21970 Published online in Wiley Online Library (wileyonlinelibrary.com). V V C 2011 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—-2011