Bordeaux‐R interactions with surfactants: thermochromic investigations of proton ionisation in cationic, nonionic and anionic surfactant solutions

Abstract

Apparent thermodynamic parameters for the hydroxy proton ionisation of Bordeaux‐R were obtained in micellar solutions using the thermochromic method. The effect of addition of the surfactants CTAB, TX‐100 and SDS was investigated in buffered solutions in the pH range of 6–13. Ionisation constants in water and in the presence of surfactants were determined spectrophotometrically and the pK′ of Bordeaux‐R in water was found to be 10.90 in the absence of surfactant. However, at concentrations above critical micelle concentration, pK′ dropped to 10.14 with CTAB, increased to 11.29 with TX‐100 but was insensitive to SDS addition. Standard enthalpies and entropies of ionisation were obtained using the thermochromic method. This method, in conjunction with pK and spectral measurements and comparison with different azo dyes, has been shown to provide detailed information on the mechanism of dye–surfactant interaction.

Effect of surfactant on the TiO 2 microencapsulation of Thermochromic materials

“…We have carried out an extensive literature survey before choosing the concentration of surfactants that are critical for the effective encapsulation of the CDTCM by the titania shell. Based on reference [25], Khamis et al, demonstrated that the CTAB critical micelle concentration (CMC) of 1.0 mM significantly changed the values of the pK acidity constant, the enthalpy, and the entropy of ionization of Bordeaux‐R. In another article, by Javid et al,, 47 the authors demonstrated that the concentration of the CTAB changed the zeta size.…”

“…The above references suggest that the concentration affects micelle formation, and that it is better for the concentration of the systems to be above the critical micelle concentration (CMC). Hence, we have chosen to work with only one concentration above the CMC for each surfactant, above 1.0 × 10 −3 mmoleL −1 for the cationic CTAB surfactant, 25 above 3.0 × 10 −3 mmoleL −1 for the anionic SDBS surfactant, 49 and above 0.2 × 10 −3 mmoleL −1 for the non‐ionic hexadecanol surfactant 50 . In addition, we have also tested the various concentrations of the TiO 2 precursor with respect to the fixed amount of the surfactant (eg, TTIP: CTAB), to understand the effective encapsulation of the CDTCM.…”

“…The process for the establishment of a core‐shell structure requires solubilization of the core in the surfactant solutions for micelles formation with the core species. Several types of surfactants, such as CTAB, SDBS, SDS, Hexadecanol, 25,26 are explored. It is important to select a surfactant that produces better micelles for a specific core system.…”