3.1.1. FT-IR Analysis

Clay surface changes are identified using FT-IR analysis [27,28]. The FT-IR spectra of the unmodified, Na-modified, and organically modified clay from the CCIn and RCKh are shown in Figures 2 and 3, respectively. From Figure 2, the infrared spectrum of commercial clay, the band in the OH-stretching region at 3628 cm<sup>−</sup><sup>1</sup> is attributed to the hydroxyl groups coordinated to Al+<sup>3</sup> octahedral cations (Al-OH) [28]. At 3439 cm<sup>−</sup><sup>1</sup> and 1646 cm<sup>−</sup>1, respectively, the OH-stretching and -bending vibrations of the adsorbed water molecules were seen [29]. Additionally, a band at 522 cm<sup>−</sup><sup>1</sup> is for Al–O–Si deformation, and a band width at 1033 cm<sup>−</sup><sup>1</sup> is for the clay's Si–O stretching vibrations. Additionally, a wide weak band at 462 cm<sup>−</sup><sup>1</sup> has been linked to Si–O–Si deformation [28,30,31]. Absorption bands for water molecules were seen at 3440 and 1650 cm<sup>−</sup>1. The bands for the deformations of Al–O–Al and Si–O–Si are situated at 523 and 464 cm<sup>−</sup>1, respectively.

**Figure 2.** FT-IR spectra of CCIn, NaCIn, OCIn, and CPC from CCIn modification.

**Figure 3.** FT-IR spectra of RCKh, NaCKh, OCKh, and CPC from RCKh modification.

The asymmetric and symmetric stretching vibrations of the (C–H) in the alkyl group of CPC have significant sharp peaks at 2924 and 2851 cm<sup>−</sup>1, respectively [32]. These two distinct, strong bands are unmistakably an indication of the intermolecular interactions that take place between neighboring alkyl chains of the organic surfactant (CPC) in clay galleries that have been treated with sodium. Additionally, a new peak for the aromatic (C = C) stretching vibrations of CPC molecules has been identified at 1491 cm<sup>−</sup><sup>1</sup> [33]. In addition to the Si–O vibrations' strong broadband properties, which were seen at 1032 cm<sup>−</sup>1, the OH groups of water's asymmetric stretching and bending vibrations were visible at 3441 cm<sup>−</sup><sup>1</sup> and 1640 cm<sup>−</sup>1. The success of the CPC cation intercalation between silicate layers and the organic alteration of NaC by CPC were both validated by all of these shifts and modifications in the OC spectrum [34]. Figures 4 and 5 for the CCIn and RCKh, respectively, display the FT-IR spectra for all synthesized PS/OC nanocomposites (PCNs) and their derivatives. These spectra show the presence of OC in the polymer matrix. The absorption bands emerged in these spectrums at the same places of the polystyrene matrix with little shifting, while some novel band alterations were attributed to the OC structure [34,35]. Two absorption bands related to the aromatic stretching vibration of sp<sup>2</sup> can be seen in the PS spectrum at 3059 and 3027 cm<sup>−</sup><sup>1</sup> (C–H). Additionally, at a wavelength from 2923 to 2852 cm<sup>−</sup>1, there are two powerful absorption bands that are connected to the asymmetric/symmetric vibrations of the aliphatic (C–H) stretching of (–CH2).

**Figure 4.** FT-IR spectra of PS, 1–5% wt.% PCN, and OCIn using CCIn.

**Figure 5.** FT-IR spectra of PS, 1–5% wt.% PCN, and OCKh using RCKh.

Additionally, it was discovered that in all the PCN spectra, the aromatic ring stretching vibrations of (C = C–C) had absorptions between 1492 and 1600 cm<sup>−</sup>1, and their overtone bands were seen between 1945 and 1746 cm<sup>−</sup>1. For the Indian and Khulays clay types, as well as for all manufactured nanocomposites (1–5% wt.% PCNs), the evident change in the weak band of pure PS at 3652 cm<sup>−</sup><sup>1</sup> was noted, especially in the case of the 5% PCN. Additionally, for all the nanocomposites, the overlap with the aliphatic and aromatic C–H stretching of PS is to blame for the removal of the CH2 stretch peak for OC. Additionally, it was noted that the form of the CH2 bending peak for PS at 1027 cm<sup>−</sup><sup>1</sup> changed, and it was particularly obvious in the case of the 5 wt.% PCN. These alterations all pointed to the successful intercalation between the OC and PS matrices. Additionally, the overlap with the aliphatic and aromatic C–H stretching of PS is to blame for all the nanocomposites' elimination of the CH2 stretch peak for OC.
