## 3 Results and Discussion
### Interaction between the Cationic Modifiers and the Reactive Dyes
#### 3.2.3 Investigation of Dye-Polymer Precipitates through XPS Spectroscopy  
The estimation of the ratio between the species of dyes and the VBCTEAM units in the solid precipitates is of importance since it evaluates the number of dye molecules that each polymeric chain can uptake. This factor is not straightforward, and it is critical in terms of both scientific knowledge and applications since each dye possesses different active sites and may pose specific steric hindrances when interacting with the polymer chains. The solid precipitates obtained at a mixing dye/polymer charge ratio fixed at D\({}^{-}\)/P\({}^{+}\) = 1 were investigated through XPS spectroscopy. Figure 8 depicts the N1s spectral region of the XPS spectrum of the NR-copo precipitate. The accumulated spectrum consists of bands assigned to both quaternary and non-quaternary nitrogen atoms. The non-quaternary nitrogen contribution at 399.5 eV is attributed to the dye Novacron Ruby S-3B, a band that is well separated from the respective one of the quaternized nitrogen of VBCTEAM units located at a binding energy of 402 eV. This separation can be useful not only for qualitative but also for quantitative analysis in the case of binary system  
Figure 7: ATR-FTIR spectra of the dye-polymer precipitate of the binary systems of (**a**) P(VBC-co-VBCTEAM53) and (**b**) VVBCTEAM with Remazol Brilliant Blue R. The spectra of the constituents are also given for comparison. study or/and the study of dyed cotton (see Section 3.3). Regarding this particular binary system, an almost equal amount of nitrogen contribution can be detected (N\({}^{+}\)/N\(\sim\)1.2/1). Considering that this dye contains seven nitrogen atoms, whereas the VBCTEAM unit contains only one nitrogen atom, this result indicates a ratio of one Novacron Ruby S-3B dye molecule for every \(\sim\)5.8 VBCTEAM units, namely close to stoichiometric charge ratio, since the dye contains five negatively charged units. The same ratio value was estimated for the binary system of the same dye with PVBCTEAM (NR-homo) after the calculation of the corresponding intensity ratio in the spectrum shown in Figure S2. Sulfonates (SO\({}_{3}^{-}\)) and sulfate (SO\({}_{4}^{-}\)) of the Novacron Ruby S-3B molecule in Figure 9a have some noticeable differences when compared to the corresponding spectrum of Remazol Brilliant Blue R binary system. These slight changes are attributed to the differentiation of the chemical environment of the anionic groups, after the electrostatic interaction. In this direction, 0.2-0.3 eV increase at FWHM of the overall sulfur peak can be justified, while the peak position remains constant. These changes are mainly found in the Novacron Ruby S-3B system that contains four sulfonate groups, in which some may not interact due to steric hindrance. The sodium 1s orbital peak at 1072 eV, in Figure 9b, is particularly strong in the Novacron Ruby S-3B spectrum indicating the counterions of the existing five anionic sites, while it is very weak in the case of the binary system. In the chlorine 2p orbital peak in Figure 10, there are multiple contributions of chlorines Cl\({}^{0}\) of both the Novacron Ruby S-3B dye (199 eV) and VBC units for the case of the cationic copolymer (200 eV), while the chlorine counterions Cl' of VBCTEAM units are observed at 197 eV. In the case of the binary system, the Cl' contribution is severely depressed. This disappearance of both sodium (dye) and chlorine (polymer) counterions indicates the strong tendency for the cationic polymer to interact with the reactive dye through electrostatic interactions. The replacement of Na\({}^{+}\) ions with the cationic units of the polymer in the binary system is in agreement with the ATR-FTIR spectroscopic results that indicate alterations in the local environment of the sulfonate/sulfate groups. Figure 8: XPS spectra of Nitrogen orbital 1 s for the copolymer, the dye Novacron Ruby S-3B and the binary system. Thin lines represent constituent peaks after a fitting process (blue colored) and their sum (pink colored).