## 2 Methods of Simulation  
To investigate the interaction between the montmorillonite layer and acrylic acid or acrylate anions, molecular dynamics simulations were performed. The composition of the montmorillonite layer was given by the formula Na\({}_{0.75}\)[Si\({}_{7.75}\)Al\({}_{0.25}\)][Al\({}_{3.5}\)Mg\({}_{0.5}\)]O\({}_{20}\)(OH)\({}_{4}\). This is a simplified composition of Na-montmorillonite (Wyoming) [16]. There is little experimental work that accurately describes the structure of montmorillonite. The initial model of the mineral layer was built on the base structural data reported by [PERSON] et al. [17], which is similar to Na-montmorillonite. Figure 2a shows the unit cell of montmorillonite from [17] of composition CS\({}_{0.62}\)[Al\({}_{3.01}\)Fe(III)\({}_{0.41}\)Fe(II)\({}_{0.04}\)Mg\({}_{0.54}\)][Si\({}_{7.8}\)Al\({}_{0.2}\)]O\({}_{20}\)(OH)\({}_{4}\). The octahedral positions of Al can be substituted by Mg and Fe, and tetrahedral Si positions can be substituted by Al. Cesium positions in this unit cell are only partially filled by Cs (occupancy equal to 0.08). This material has a C/2m space group, and their unit call parameters are a = 5.181, b = 8.945, c = 12.34 A, \(\alpha\) = \(\gamma\) = 90, \(\beta\) = 99.62\({}^{\circ}\).  
Figure 1: Scheme of some of the possible interactions of montmorillonite in calcium and sodium-activated bentonite with the chains of poly(acrylic acid): surface and edge adsorption combined with the intercalation [15].  
The supercell of the montmorillonite layer was created by the multiplication of the unit cells in x and y directions by 16 \(\times\) 8. The Cs has been replaced with the appropriate amount of Na. Part of the Al positions was substituted with Mg and part of the Si was substituted with Al to obtain Na\({}_{0.75}\)[Si\({}_{7.75}\)Al\({}_{0.25}\)][Al\({}_{3.5}\)Mg\({}_{0.5}\)]O\({}_{20}\)(OH)\({}_{4}\) stoichiometry. The initial layer dimensions were 82.90 \(\times\) 71.56 A. Water molecules were placed around the montmorillonite layer so that the initial model had 12,896 atoms. The initial simulation box height was about 30 A. The CVFF-interface force field [19] was used to describe the interaction between atoms in the system. This force field is successfully used for modeling clay minerals-organics interfaces [19; 20; 21; 22]. Initial models of acrylic acid, acrylate anions, and water molecules were built based on structural data from [18; 23]. Classical molecular dynamics simulations were performed using LAMMPS software [24]. The periodic boundary conditions were used to remove the surface effect of the simulation box. The simulations were performed in terms of constant pressure equal to 1 bar and temperature equal to 300 K. At first, systems were relaxed during 70 ps with the time step equal to 0.005 fs. Such a long time was necessary not only to relax the montmorillonite layer but also to homogenize and relax the water around the montmorillonite. Then, the acrylic acid or sodium acrylate molecules were added to the system randomly at a distance greater than 10 A from the montmorillonite layer. One molecule was added every 2.5 ps. In total, 40 molecules in each simulation were added into the system. For the next 63.00 ps, data of the molecules' localization was collected. The systems were visualized using Ovito software [25]. Carbon quantity contour maps (located in acrylic acid or acrylate anions) on the xy-plane parallel to the montmorillonite layer were created using python library matplotlib [26]. The size of the bins in which the carbon atoms were counted to create contour maps was 4 \(\times\) 4 A.