Research Paper Laponite RD/polystyrenesulfonate nanocomposites obtained by photopolymerization Tatiana Batista a , Ana-Maria Chiorcea-Paquim b , Ana Maria Oliveira Brett b , Carla C. Schmitt a , Miguel G. Neumann a, ⁎ a Instituto de Química de São Carlos, Universidade de São Paulo, Caixa Postal 780, 13560-970 São Carlos SP, Brazil b Departamento de Química, Faculdade de Ciências e Tecnologia, Universidade de Coimbra, Portugal abstract article info Article history: Received 7 June 2010 Received in revised form 31 March 2011 Accepted 8 April 2011 Available online 11 May 2011 Keywords: Clay/polymer nanocomposites Laponite Polystyrenesulfonate The present paper describes the synthesis and characterization by dynamic light scattering, X-ray diffraction, scanning electron microscopy and atomic force microscopy of Laponite RD/Sodium polystyrenesulfonate nanocomposites obtained by radical photopolymerization initiated by the cationic dye safranine. The presence of the clay mineral does not affect the hydrotropic aggregation of the monomers, but allows a better deaggregation of the initiator molecules, decreasing the quenching of the excited states that leads to the radicals that initiate polymerization. Increasing the amount of clay mineral loading in the polymerization mixture promotes higher monomer conversion and faster polymerization. The size of the nanocomposite particles, measured by light scattering decreases from 400 to 80 nm for clay mineral loadings of 1.0 wt.%. The X-ray diffraction patterns indicate that the clay mineral does not present a regular crystalline structure in the nanocomposite. Atomic force microscopy studies show films of sodium polystyrenesulfonate polymer with embedded Laponite platelets in its structure, forming 1–8 nm height and 25–100 nm diameter aggregates. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Clay minerals are extensively used in a wide range of applications. They are key components in the formulation of ceramic products, cement, drilling fluids, paints, and paper, among others. An important characteristic that clay minerals are able to provide in such uses is an adequate particle dispersion which is necessary to obtain uniform and stable systems (Pacula et al. 2006). Smectites are aluminosilicate minerals that have layered structures, which allow the intercalation of other compounds forming novel materials that present nanostruc- tures with new properties that might be interesting in several fields ((Annabi-Bergaya 2008; Lagaly 1986; Pinnavaia 1983). The incorporation of clays in polymers for improving their physical and mechanical properties is an important trend in polymer chemistry. It is known that the fully exfoliated platelet structure of nanoclays dispersed in polymer matrices confers excellent mechan- ical and barrier properties (Okada and Usuki 2006; Shi et al. 1996; Tsai et al. 2008). A wide range of polymers derived from monomers like epoxides (Wang and Pinnavaia 1994), styrene (Fu and Qutubuddin 2000), ethers (Pinnavaia et al. 1994), and acrylamide (Muzny et al. 1996) has been used with raw or synthetic clay minerals for development of polymer layered silicate nanocomposites. Polymer- layered silicate nanocomposites are currently prepared in four ways: in situ polymerization, intercalation from a polymer solution, direct intercalation on polymer and sol–gel technology (Okada and Usuki 2006). The in situ polymerization technique was first developed by the Toyota Group to make Nylon-6 nanocomposites from caprolactam monomers (Usuki et al. 1993). A comprehensive review of the synthesis and mechanisms of in situ clay/polymer nanocomposites preparation has been published recently (Tasdelen et al. 2010). Clay/polymer nanocomposites can be classified in three catego- ries: conventional particulate composites (the clay mineral particles exist in their original aggregated state with no insertion of polymer matrix between the layers), intercalated nanocomposites (only a few molecular layers of polymer are incorporated in the clay mineral structure, which might alter the properties of the composite (Annabi- Bergaya 2008)) and exfoliated nanocomposites (the individual clay mineral layers are separated and dispersed in a continuous polymer matrix) (Qutubuddin and Fu 2001). The latter yield the maximum improvement in the nanocomposite properties, as maximal rein- forcement is achieved. The dispersion or exfoliation of clay mineral particles in monomers or polymer matrixes involves three steps: wetting of the surface, intercalation of monomers or polymers into the clay mineral interlamellar spaces, and exfoliation of the clay mineral layers (Qutubuddin and Fu 2001). Polymerization in ordered domains results in different kinetic behaviour (Clapper and Guymon 2006; Uhl et al. 2004). Therefore, it may be assumed that the ordering of the platelets in the clay mineral particles may induce changes in the polymerization behaviour that could influence the final nanocomposite properties. In addition, the relatively large surface of the clay mineral particles could also affect Applied Clay Science 53 (2011) 27–32 ⁎ Corresponding author. Tel.: +55 16 33739940; fax: +55 16 33739952. E-mail address: neumann@iqsc.usp.br (M.G. Neumann). 0169-1317/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.clay.2011.04.007 Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay