Surface Structural Characterization and Mechanical Testing by Nanoindentation Measurements of Hybrid Polymer/clay Nanost
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Mi-kyoung Park and Chuanjun Xia Department of Chemistry, University of Alabama at Birmingham, Birmingham, Alabama 35294-1240
Rigoberto Advinculaa) Alabama Tri-campus Materials Science Program and Department of Chemistry, University of Alabama at Birmingham, Birmingham, Alabama 35294-1240 (Received 3 October 2001; accepted 3 April 2002)
Nanostructured montmorillonite/poly(diallyldimethylammonium chloride) multilayer thin films were fabricated up to 100 layers thick by stepwise alternating polyelectrolyte and clay deposition from solution. The structure and morphology of the films were characterized by x-ray diffraction, ellipsometry, atomic force microscopy, and quartz crystal microbalance ex situ and in situ measurements. The mechanical properties were tested by nanoindentation. The hardness of the multilayer thin film was 0.46 GPa. The thin film’s modulus was correlated to its ordering and anisotropic structure. Both hardness and modulus of this composite film were higher than those of several other types of polymer thin films.
I. INTRODUCTION
The structure and property of polyelectrolyte/clay selfassembled thin film have been intensively and extensively investigated. Not only are they of great interest as nanostructured, precisely controllable, and well-ordered multilayer thin films prepared by a simple layer-by-layer method,1 but they also have tremendous potential applications as optical and electronic materials.2,3 Furthermore, they are also ideal systems for the study of the various theories in interface science and intercalation thermodynamics of organic species in confined and tethered environments.4 A great deal of work has been done regarding the characterization of these nanocomposite films. Some silicate clay species, such as montmorillonite and hectorite, are negatively charged upon hydration and possess unique layered morphology. Several researchers have reported the incorporation of these clay sheets into the alternate polyelectrolyte deposition (APD) approach since 1994.5 In-depth structural investigation of film thickness and interlayer spacing of clay particles was accomplished by Kotov and Kleinfeld et al. through a series of surfacesensitive techniques such as surface plasmon spectroscopy (SPS), x-ray reflectivity, and x-ray diffraction a)
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J. Mater. Res., Vol. 17, No. 7, Jul 2002 Downloaded: 24 Feb 2015
(XRD), etc.6,7 The mechanism of the alternate selfassembly formation was proposed by the above researchers. Film surface smoothness is of crucial importance for real commercial applications such as packaging and coatings. Therefore, the surface morphology of the multilayer thin film has been well studied by atomic force microscopy (AFM), and mathematical modeling of the layerby-layer structural development can be carried out. The mechanism for the high degree of order of this kind of multilayers has also been suggested.8,9 Very recently, the organic species intercalated into this system has been extended to cha
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