## 3 Results and Discussion
### Role of the Cationic Modifier in the Dyeing Process of Cotton
The ability of this surface technique further demonstrates the potential of the cationic modification process to retain large quantities of dye (more than an order of magnitude compared to the unmodified cotton) even at low temperatures. The higher degree of dyeability caused by the presence of the cationic modifier on the cotton surface is clearly resolved in Figure 12. Unmodified fabrics dyed using the typical procedure with and without salt exhibit low dyeability at low temperatures; the presence of salt results in a slightly higher dyeability. In comparison, modified fabrics exhibit high dyeability at lowtemperatures even without the presence of salt. Apart from being more vivid, the color of these fabrics is also particularly uniform. Extensive colorimetric studies performed on dyed fabrics modified by a series of cationic modifiers similar to the ones used in the current study can be found in [52]. In the next paragraphs, the XPS study of the pair of dyed fabrics depicted in Figure 12 will be given as a case study. The results of all other possibilities are comparable and lead to the same conclusions. The N\({}_{18}\) spectral region in the XPS spectra can be used to verify the coexistence of the components (quaternary VBCTEAM units and non-quaternary species of dyes), while the Cl\({}_{2\text{P}}\) one to reveal the interactions involved between cellulose, cationic polymer, and dye. The nitrogen existing in the dyed fabric is a combination of cotton residues and dye, as indicated by the peak at \(\sim\)400 eV in the N\({}_{18}\) spectral region of the XPS spectra (Figure 13a); the cotton residues contribution is considered much less than that of the dye. For the case of modified dyed fabrics, two peaks are resolved, at \(\sim\)400 eV assigned mainly to the dye and at \(\sim\)402 eV assigned to the VBCTEAM units. From the signal to noise ratio, it is clear that the dye retention is significantly increased after treatment, in agreement with the respective findings from the carbon 1s spectral region. Figure 11: XPS spectra of carbon orbital 1s of the untreated fabric substrate, low-temperature dyed cotton fabric (Novacron Ruby S-3B), modified fabric with PVBCTEAM, and low-temperature dyed modified fabric. Inset: low-temperature dyed fabric with and without adding salt in the dyeing bath. Figure 12: Dyed cotton fabric at low temperatures with (**a**) Novacron Ruby S-3B and (**b**) Remazol Brilliant Blue R. Comparison of the color intensity for samples with and without modification is unambiguous. For the modified fabrics the dyeing protocol without salt (S2.1) was followed. The Cl\({}_{\rm 2p}\) spectral region, Figure 13b, is indicative of the chloro-triazine sites when dyeing with the Novacron Ruby S-3B dye (at \(\sim\)199 eV). This chemical unit is one of the two sites of potential direct interaction of this particular dye molecule with cotton. In the same spectral region, the Cl atoms of the polymers containing VBC units also contribute (\(\sim\)200 eV). However, as already shown [31], their contribution to the modified fabrics cannot be observed in the XPS spectra; the latter was explained as an indication of polymer grafting on cellulose through this reactive site. Finally, the Cl\({}_{\rm 2p}\) spectral region is characteristic of Cl\({}^{+}\) at \(\sim\)198 eV. Our results reveal that no Cl\({}_{\rm 2p}\) bands are observed in the fabric, nor in the unmodified dyed fabric. The latter may be explained either by the low quantities of dye molecules retained at low-temperature processes and/or by the direct grafting of the dye to cellulose. The weak band of chlorine ions observed (at \(\sim\)198 eV) in the spectra of unmodified fabric is possibly attributed to small salt residues after the dyeing process performed in alkaline 1M NaCl solutions. The clearly resolved neutral chlorine band observed in the spectra of modified-dyed fabrics suggests a considerable fraction of unreacted dye sites.