Novel polymer nanocomposite hydrogel with natural clay nanotubes

Abstract

presence of nanoclay in aqueous system. Here, novel natural tube-like nanoparticles, halloysite nanotubes (HNTs), are firstly used as multifunctional cross-linkers for polyacrylamide (PAAm) to form a new type of organic/inorganic hybrid hydrogels. Significant improvements in mechanical properties of the PAAm-HNTs NC gels are found by the addition of HNTs as shown by the static mechanical testing and dynamic viscoelasticity measurement. HNTs are uniformly dispersed in the NC gels from the morphological result. HNTs can be intercalated by PAAm chains as observed by the X-ray diffraction result. Hydrogen bonding interactions between HNTs and PAAm are confirmed by the infrared spectroscopy and X-ray photoelectron spectroscopy. The maximum equilibrium degree of swelling (EDS) for the NC gel is 4000% and the EDS decreases with the concentration of clay nanotubes. The present work provides a novel routine for preparing NC gels using "green" onedimensional nanoparticle. The prepared NC gels have promising application in biomedical areas due to the superior mechanical properties of the gels and good biocompatibility of HNTs.Keywords Halloysite nanotubes . Hydrogel . Mechanical properties . Nanocomposite mer and inorganic nanoparticle was first proposed and fabricated by Haraguchi, a Japanese scientist, in 2002 [1]. The NC gels can be synthesized through in situ free-radical polymerization of water-soluble monomers such as acrylamide and 2-methoxyethylacrylate in the presence of nanoclay in aqueous system, in which the nanoclays act as the multifunctional cross-linking points for the polymer chains [2][3][4]. Compared with traditional organic cross-linked hydrogel, the NC gels have a unique structure and properties, for example, super optical transparency, ultrahigh tensile extensibility, high swollen ratio and stimuli sensitivities [2]. Therefore, NC gels have been found to be applicable as super-absorbent materials, biomedical materials, smart materials, and so on. A wide range of clay minerals with layered crystal structures, good water swellability, and strong interactions with the water soluble monomers are used as the inorganic component for the NC gels. Typical examples include the smectite-group clays (hectorite, saponite, montmorillonite and so on) and mica-group clays (synthetic fluorine mica). Among these, the artificially synthesized layered silicate "Laponite," with the molecular formula of [Mg 5.34 Li 0.66 Si 8 O 20 (OH) 4 ]Na 0.66 , is mostly used for the preparation of NC gels. Laponite has sufficiently small platelet size (30 nm (diameter)×1 nm (thickness)) and high swelling ability in water (about 35×) for forming clear and colorless colloid dispersion. A series of NC gels have been prepared by combining Laponite with different monomers [1,[4][5][6]. The ability of forming inorganic/organic hybrid network for NC gels depends on the interactions between the nanoclay and the monomer/polymers, such as, hydrogen bonding and/or ionic interaction. On the other hand, the NC gels cannot be obtained by the polymer...

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