# Comparison of the Properties and Structure of Montmorillonite Modified with Polyvinylpyrrolidone
###### Abstract
[29] showed that PVP is a surface stabilizer, growth modifier, nanoparticle dispersant, and reducing agent during the colloidal synthesis of nanostructures. The growth and morphology of nanoparticles depend primarily on the molecular weight of PVP and its amphiphilic nature. In this way, it is possible to regulate the solubility of the obtained nanostructures in various solvents, provide selective stabilization of their surface [32; 33; 34], and even gain access to kinetically controlled growth conditions. [PERSON] and [PERSON] [35], using the methods of X-ray diffraction and desorption of \({}^{109}\)Cd and \({}^{85}\)Sr, showed that PVP is adsorbed on the surface of MMT and attaches to tetrahedral sheets. Moreover, with a decrease in the number of solvent layers in the interlayer space of MMT, the amount of adsorbed PVP decreases. [PERSON] et al. [36; 37] also studied the adsorption of PVP on the MMT surface. The formation of intercalated montmorillonite tactoids and the growth of basal spacing (d001) with an increase in the adsorbed PVP amount were confirmed. The formed polymer layer on the surface of MMT significantly affects its adsorption capacity, especially the degree of binding of anionic and neutral organic chemicals. [PERSON] et al. [38] showed that PVP is adsorbed on the 001 surfaces of layered silicate (smectite) with the formation of a layer 5-6 A thick, and the PVP chains that are directly connected to the silicate surface are more rigid and ordered than the outer chains. In addition, the charge in tetrahedral or octahedral positions of smectite practically does not affect the PVP structure. In most works, exfoliated nanocomposites based on MMT are obtained at a low nanoclay content, mainly from 1 to 7 wt% [39; 40; 41; 42], rarely with 20 wt% [43]. [PERSON] et al. [44] presented a method for obtaining exfoliated nanocomposites based on MMT and PVP in an aqueous solution with a high content of MMT from 50 to 67 wt%. They showed that the yield of the exfoliated nanocomposite significantly depends on the duration of mechanical stirring of the suspension, and optimal characteristics are achieved after 18 h of stirring. The nanocomposite with an MMT content of 67 wt% has significantly higher heat resistance than the original PVP. [PERSON] et al. [45] presented a method of obtaining montmorillonite intercalated with PVP (PVP K-30) in CHCl\({}_{2}\) solution at room temperature and mechanical stirring. It is shown that the yield of intercalated MMT depends on the initial mass ratio of the components in the solution and is 27%, 20%, and 15% for the PVP/MMT mass ratio of 2:1, 1:1, and 1:2, respectively. The resulting intercalated nanocomposites are recommended for use as a matrix for the sustained release of drugs and as dissolution enhancers. Therefore, the mass ratio of the components during the obtaining of MMT/PVP nanocomposites significantly affects the yield and structure of the final products. In a previous work [46], we presented a new method of MMT modification using PVP. The modification process is carried out in an aqueous solution with a mass ratio of MMT/PVP = 1:2 and subsequent solution separation into three fractions (nanocomposites of different structures). Simultaneously intercalated, flocculated, and exfoliated MMT is obtained from one prepared solution. Considering the above, this work aims to investigate the influence of the initial MMT/PVP mass ratio on the yield, structure, and thermal properties of montmorillonites obtained by this method. The work task is also to compare the structure and properties of these MMT-s with the nanocomposite of the composition MMT/PVP = 1:12, obtained similarly but without solution fractionation. This ratio of MMT/PVP is chosen because it has been established in previous work [46] that exfoliated MMT contains about 93 wt% PVP.