Structure and spectroscopic properties of organoclays doped by multiwall carbon nanotubes

Abstract

A method to modify a montmorillonite (MMT) clay mineral (CM) surface by surfactant (SA) cations with simultaneous doping by multiwall carbon nanotubes (MWNT) has been proposed. The structure and spectroscopic properties of composites based on MMT from two deposits (Cherkassy and Pyzhevsk, Ukraine) that differ in the inorganic impurity contents and cation-exchange capacities (CEC) have been investigated. Cetyltrimethylammonium bromide (CTAB) was used as the SA. According to x-ray diffraction analysis, CTA + cations intercalated into MMT interplanar spaces expand them significantly whereas MWNTs do not affect the MMT galleries due to the much larger sizes of the former. Studies of the composite materials by IR spectroscopy revealed the mutual influence of the components appearing as the ordering of near-surface layers in the aluminosilicate framework and a change in the modifier methylene chain conformation at the interphase boundary. The majority of CTAB (~90%) is shown to be located inside the MMT galleries, the packing arrangement of which depends on the CEC value and affects the interplanar distances in MMT. The alkyl chains of the CTA + cations on the outer surface of the MMT plates are sorbed by nanotubes, thus providing contact between the organoclay and MWNT surfaces.Introduction. Multi-functional heterosystems consisting of an organic component and multiwall carbon nanotubes (MWNT) are currently under intense scrutiny. The incorporation of small quantities of the latter into an organic medium changes drastically its physical properties such as electrical and thermal conductivity, mechanical and optical characteristics, etc. [1-3]. However, MWNT exhibit a high capability to aggregate. This makes it very difficult to create composites with a uniform distribution of MWNT in the organic matrix because of their lipophobic nature. MWNTs are treated with surfactants (SAs) in order to give their surface a higher affinity for the organic medium [4,5]. Another method for preparing homogeneous composites is to add nanoparticles of organoclays to the organic matrix and MWNT. It was shown [6,7] that these fillers produce a synergistic effect on the mechanical and thermal properties of nanocomposites when added simultaneously to ethylene-vinylacetate copolymer or chitosan (polysaccharide). Furthermore, the effect of adding organoclay particles and MWNT to various polymers on not only the mechanical properties of the resulting composites but also their flammability was investigated [8][9][10][11][12]. It was shown that the ability of such heterocomposites to ignite was sharply reduced even with low (~1%) concentrations of nanofillers owing to the synergistic effect produced in such systems.MWNTs were intercalated into layered clay minerals (CMs) by catalytic decomposition at 700