Systematic Study of Interfacial Interactions Between Clays and an Ionomer Yan Gao,* Namita Roy Choudhury, Naba K. Dutta Ian Wark Research Institute, University of South Australia, Mawson Lakes Campus, Mawson Lakes, Adelaide, South Australia 5095, Australia Received 17 May 2009; accepted 8 January 2010 DOI 10.1002/app.32089 Published online 11 May 2010 in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: To study the interfacial interactions between an ionomer [poly(ethylene-co-acrylic acid) neu- tralized by zinc salts (PI)] and clays, PI–clay nanocompo- sites were prepared using a solution method. Two types of commercially available montmorillonite clays respec- tively K10 and KSF were used, and were modified with organic modifiers with chain lengths of 12–18 carbons. The interactions between the PI, clays, and modifiers were evaluated through study of the structure, morphology, and properties of the PI–clay nanocomposites. We found that the modifiers were successfully intercalated into the clay layers (Fourier transform infrared spectroscopy). The clay modified with a long-chain agent showed an exfoli- ated nature in the nanocomposite. The thermal stability and storage modulus of PI were improved greatly by the addition of the clays, especially when the long-chain modi- fier was used (thermogravimetric analysis and dynamic mechanical analysis). The differential scanning calorimetry results show that clay layers are inserted into the clusters because of solvent-directed morphological evolution, so the transition of the ionic domains and the crystallinity of PI are changed. The interaction between PI, the modifier, and the silicate layer played an important role in the determina- tion of the properties of the nanocomposites. V C 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 3395–3405, 2010 Key words: polymer interfaces; ionomers; nanocomposites; organoclay; thermal properties INTRODUCTION Organic–inorganic nanocomposites (NCs) are multi- functional materials with a wide range of interesting properties, and they overcome the poor adhesion/ interface problems of microcomposites, which stem from the ability to control the nanoarchitecture of materials at a very early stage of preparation. 1–4 Sev- eral routes, such as intercalation, 5–8 electrocrystalli- zation, 9 and sol–gel processing, 10,11 can be used to synthesize hybrid materials. Intercalation involves the use of a unique, self-assembling inorganic mate- rial, such as clay, to prepare organic–inorganic hybrid composites, which can be used as host latti- ces for organic materials because of their platy mor- phology with a high aspect ratio (20–2000). 12–23 Weak dipolar and van der Waals forces exist between the clay layers, which result in galleries. The dispersion of clay particles in a polymer ma- trix can result in the formation of two types of NCs: intercalated and exfoliated. Intercalated clay compo- sites have a definite structure formed by the interca- lation of polymers into inorganic layered host latti- ces, and their properties resemble those of the ceramic host. In contrast, exfoliated polymer–clay NCs have low clay contents, with a separation between the galleries and layers that depends on the polymer content of the composite and the properties of the nanoconfined polymer. The properties of the polymer–clay NCs strongly depend on the interac- tions between the polymer and the clays. 24 Montmorillonite (MMT) has a strong intercalation ability to accommodate a number of molecules or polymer chains to become compatible with polymers at a molecular level. A clay with an excess negative charge is miscible with a hydrophilic polymer. To render it compatible with hydrophobic polymers, some organic swelling agents have been used to modify its surface characteristics. 25–33 The conforma- tions of the organic swelling agents in the clay inter- layer space depend on the chain length and their cation-exchange capacity. Yano et al. 34 reported that ammonium ions with 10–12 carbon atoms were suitable for the modification of MMT dispersed in dimethylacetamide. Increasing the carbon number of the surfactant decreased the hydrophilicity of Additional Supporting Information may be found in the online version of this article. *Present address: Institute of Materials Engineering, Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales, Australia. Correspondence to: N. R. Choudhury (namita.choudhury@ unisa.edu.au). Journal of Applied Polymer Science, Vol. 117, 3395–3405 (2010) V C 2010 Wiley Periodicals, Inc.