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Polymer-layered silicate nanocomposites (PLSNs) are of great interest nowadays because they exhibit substantial improvement in mechanic, thermal and other properties compared to the basal polymer. PLSNs consist of a polymer which is bonded to a layered silicate, usually smectite. In order to explain properties of PLSNs it is important to understand the structure of the polymer and the way it is adsorbed to the surface of the mineral.

Polyvinylpyrrolidone (PVP) is a nonionic polymer with amphiphilic character (Sun & King, 1996). Hydrophilic imidic group N-C=O lies next to carbons of the pyrrolidine ring and to the polymer backbone part that is hydrophobic. It is a polymer widely used along with clay minerals as PLSN. PVP is also of interest to geochemists, soil scientists and clay mineralogists because of its specific interactions with clay minerals. It has been studied e.g. as a surfactant which stabilizes colloidal clay particles, as adsorbent which intercalates into clay particles or leads to their exfoliation, allowing to quantify the content of smectite, to measure the thickness distribution of fundamental particles or to quantify the surface areas and thus the content of smectite. Despite the long history of the investigations of PVP adsorption on smectites, the structure and the mechanism of this sorption still are not clear.

Molecular simulations shows that, if there is no water in the system, PVP forms a layer connected to the smectitic surface with C=O groups bonded to the Na⁺ counterions. Comparison of total energies for different configurations shows that, if water molecules are included, water surrounds Na⁺ ions and PVP is adsorbed through the water bridges to the Na⁺ counterions on the surface of smectite. We obtained a good agreement between the experimental (Blum & Eberl, 2004) and calculated basal spacing for one and two layers of PVP intercalated in smectite. Inclusions of water molecules leads to slight increase of basal spacing distances. Molecular modeling calculations were carried out in DLPOLY2 modeling environment.

Blum A.E., Eberl D.D. (2004) Measurement of clay surface areas by polyvinylpyrrolidone (PVP) sorption and its use for quantifying illite and smectite abundance. Clays and Clay Minerals, 52, 589-602.

Sun T., King H.E. (1996) Aggregation behavior in the semidilute poly(N-vinyl-2-pyrrolidone)/water system. Macromolecules, 29, 3175-3181.