Comparison of solution intercalation and melt intercalation of polymer±clay nanocomposites Zhiqi Shen a , George P. Simon b, * , Yi-Bing Cheng b a DBCE, CSIRO, P.O. Box 56, Highett, Vic. 3190, Australia b School of Physics and Materials Engineering, Monash University, P.O. Box 69M, Clayton, Vic. 3800, Australia Received 24 January 2002; received in revised form 18 March 2002; accepted 21 March 2002 Abstract Polymer±clay nanocomposites of polyethylene oxide)/Na-montmorillonite PEO/MMT) and PEO/organo-modi®ed bentonite B34) systems prepared via solution intercalation and melt intercalation have been compared by X-ray diffraction and Fourier transform infrared FTIR)analysis.Thegallerysizeofsolution-intercalatedhybridsinbothPEO/MMTandPEO/B34systemsincreaseswithPEOcontentupto a plateau level at 15%. However, the gallery size of melt-intercalated PEO/MMT and PEO/B34 hybrid remains the same regardless of the PEO concentration. FTIR analysis shows no difference in spectrum of samples prepared by solution intercalation compared to melt intercalation. The PEO conformation in the PEO/clay intercalated hybrids is concluded to be a distorted helical structure. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Polymer±clay nanocomposites; Melt intercalation; Solution intercalation 1. Introduction Intercalation of polymers in layered hosts, such as mica type silicates has proven to be a successful approach to synthesize nanophase organic±inorganic hybrids. The preparativemethodsaredividedintothreegroupsaccording tostartingmaterialsandprocessingtechniques:insitupoly- merization intercalation, solution intercalation and melt intercalation. Polymerization intercalation is a method based on the use of one or more monomers that may be in situ linearly polymerized or crosslinked and was the ®rst method used to synthesize polymer±layered silicate nano- composites based on polyamide 6 [1,2]. It is still widely used in many studies, especially in thermosetting poly- mer±layered silicate nanocomposites. However, it is not relevant to the work presented in this paper, and will not bediscussedfurther.Polymersolutionintercalationisbased onasolventsysteminwhichthepolymerissolubleandthe silicate layers are swellable [3]. The layered silicate is ®rst swollen in a solvent, such as water, toluene or chloroform. When the polymer and silicate solutions are mixed, the polymer chains intercalate and displace the solvent within the interlayer of the silicate. Upon solvent removal, the intercalated structure remains, resulting in hybrids with nanoscale morphology. Water soluble polymers, such as polyvinyl alcohol [3], polyvinyl pyrrolidinone) [4], poly- ethylene oxide) PEO) [5,6] and polyethylene vinyl alcohol) [7] have been intercalated into clay galleries via this method. Examples including non-aqueous solvents are of nanocomposites of a poly1-lactide)±clay system [8] or PEO [9] in chloroform as a cosolvent, and polyimide± aluminum nitride system in N-methylprolidinone as the suspension media [10] and high-density polyethylene with xylene and benzonitrile [11]. Nematic liquid crystal poly- mer±clay nanocomposites have also been prepared in various organic solvents, such as toluene and DMF [12]. The thermodynamics involved in solution intercalation are as follows. For the overall process, in which polymer is exchanged with the intercalated solvent in the gallery, a negative variation in the Gibbs free energy is required. The driving force for polymer intercalation into layered silicate fromsolutionistheentropygainedbydesorptionofsolvent molecules, which compensates for the entropy decrease of the con®ned, intercalated chains [13]. Intercalation only occurs for certain polymer/solvent pairs via solution inter- calation. It is a good way to intercalate polymers with little ornopolarityintolayeredstructures,andfacilitatesproduc- tion of thin ®lms with polymer, oriented-clay intercalated layers. However, in a commercial sense, it involves the use Polymer 43 2002) 4251±4260 0032-3861/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII:S0032-386102)00230-6 www.elsevier.com/locate/polymer * Corresponding author. E-mail addresses: shirley.shen@csiro.au Z. Shen), george.simon@spme.monash.edu.au G.P. Simon), yibing.cheng@spme.monash.edu.au Y.-B. Cheng).