## Result and Discussion
### X-Ray Diffraction  
The XRD patterns of MMT, OMMT, PS, PS-OMMT-1, PS-OMMT-3 and PS-OMMT-5 are shown in Figure 3A-F, respectively. As shown in Figure 3A, a typical MMT diffraction peak appeared at 20 = 7.28\({}^{\circ}\), corresponding to a basal interlayer distance of 1.21 nm according to Bragg's law. After modification by SLS, as shown in Figure 3B, the diffraction peak of OMMT shifted to 20 = 5.79\({}^{\circ}\), suggesting that the interlayer distance had increased to 1.52 nm. This result indicated that the anionic surfactant molecules were successfully intercalated into the MMT interlayer spaces, thereby expanding the interlayer distance and causing the surface properties of MMT to change from hydrophilic to hydrophobic.  
Figure 3: X-ray diffraction patterns of (**A**) MMT, (**B**) OMMT, (**C**) PS, (**D**) PS-OMMT-1, (**E**) PS-OMMT-3 and (**F**) PS-OMMT-5.  
Figure 2: FTIR spectra of (**A**) MMT, (**B**) OMMT, (**C**) PS and (**D**) PS-OMMT-3.  
However, there is currently no universal understanding of the mechanism for the intercalation of an anionic surfactant into MMT. [PERSON] proposed that the intercalation of the anionic surfactant was due to the formation of ion pairs between the surfactant anions and hydronium ions or Na\({}^{+}\) and Ca\({}^{2+}\) counterions and that these ion pairs then entered the interlayer spaces in different arrangements [19]. However, the isomorphous substitution of Mg\({}^{2+}\) for Al\({}^{3+}\) or, rarely, Al\({}^{3+}\) for Si\({}^{4+}\) generates a net negative charge on the surface of MMT layers [32]. Furthermore, many hydroxyl groups are present at the edges of MMT, and few are present on the external and internal surfaces due to electrostatic interactions with hydronium ions. In addition, in acidic media, the negative charge density on the MMT surface will decrease, and the number of hydroxyl groups will increase because a large concentration of hydronium ions enter the interlayer space of the MMT [19]. Therefore, the anionic surfactant could generally intercalate into the MMT interlayer spaces through the replacement of or interaction with hydroxyl groups at the MMT layer edges (see stage A in Figure 1). As surfactants are inserted into the clay layers, the electrostatic repulsion between the layers gradually increases, resulting in an increase in the spacing between the clay layers. Thus, the anionic surfactant transforms MMT to OMMT with enlarged interlayer spacing, into which the styrene monomer can easily enter and polymerize.  
As shown in Figure 3C-F, the disappearance of the MMT diffraction peaks in these patterns indicated that the PS chains were inserted into the OMMT gallery, which is the interlayer space of OMMT, and destroyed the ordered clay structure during the emulsion polymerization process. In the PS-OMMT nanocomposites, no OMMT diffraction peaks were visible because the OMMT tactoids were likely exfoliated and dispersed in a disorderly fashion into the PS matrix at the molecular level or because the clay interlayer distances were greater than 6 nm [33]. However, the absence of XRD peaks does not necessarily indicate complete exfoliation of the clay layers [34]. Thus, the dispersion and degree of exfoliation of the clay layers, as well as the microstructure morphology in the matrix, were further corroborated by TEM analysis. TEM micrographs of the PS and nanocomposite samples are shown in Figure 4.