Foreign Cooperating Institutions - Institute of Inorganic Chemistry ...

Organoclays and their applications
J. Hrachová, Ľ. Jankovič, P. Komadel, J. Madejová, H. Pálková
Montmorillonites (MMT), the main minerals in bentonites belonging to smectite group, are
often used in many industrial applications, either in their natural form or after appropriate
modification. Natural smectites with inorganic exchangeable cations, e.g. Ca 2+ or Na + , and
their high affinity to water gives rise to hydrophilic character of smectite surface.
Replacement of inorganic by organic (alkylammonium) cations changes the clay mineral
surfaces to more hydrophobic. Final properties of organo-modified MMTs (organoclays)
depend on their layer charge, the type of the organic cation used; the cation/clay mineral ratio,
etc. For such materials higher stability upon mechanochemical or acid treatment was observed
[1,2]. Montmorillonites in their natural forms are considered ineffective adsorbents of nonpolar
organic compounds polluting frequently surface water because these compounds cannot
effectively compete with highly polar water for adsorption sites on smectite surfaces.
However, after exchange with organic cations with long alkyl chains adsorption on the
smectites has been impressive. On the other side, smectite
modified with small alkylammonium cations did not display
much better adsorption abilities compared to their natural
forms. Improvement was achieved only for low charged
smectites. Nowadays, montmorillonite is the most widely used
clay mineral as nanofiller because of its cation-exchange
capacity and large active surface area when sufficiently
delaminated. The layer thickness is ~1 nm, while the lateral
dimensions of the layers vary up to several microns or even
more, i.e. at least one dimension of the filler is in the
nanometer range. Of particular interest is recently developed
nanocomposite technology consisting of interactions of a
polymer with an organoclay [3] Alkylammonium or
alkylphosphonium cations in the organoclays lead to a
decrease of the surface energy of the inorganic host and
improve the wetting of the filler surface by polymer matrix,
resulting in larger interlayer spacing. Additionally, these
cations can provide functional groups that may react with the
polymer matrix, or even initiate the polymerization of
monomers to improve interactions on the interface between
the inorganic and the polymer matrix and to advance beneficial
properties of nanocomposites.
10
Configuration of organic
cations within interlayers
of smectites
Further information: J. Hrachová: jana.hrachova@savba.sk
1. Hrachová J., Madejová J., Billik P., Komadel P., Fajnor V.Š.: J. Coll. Interf. Sci. 316, 589–595,
2007
2. Madejová J., Pálková H., Pentrák M., Komadel P.: Clays Clay Miner. 57, 392-403, 2009
3. Hrachová J., Komadel P., Chodák I.: J. Mat. Sci. 43, 2012–2017, 2008