Self-assembling systems based on amphiphilic alkyltriphenylphosphonium bromides: Elucidation of the role of head group

• Published in: Journal of colloid and interface science 2012-02, Vol.367 (1), p.327-336
• Main Authors: Gainanova, Gulnara A., Vagapova, Guzalia I., Syakaev, Victor V., Ibragimova, Alsu R., Valeeva, Farida G., Tudriy, Elena V., Galkina, Irina V., Kataeva, Olga N., Zakharova, Lucia Ya, Latypov, Shamil K., Konovalov, Alexander I.
• Format: Article
• Language: English
• Subjects: Agglomeration; Aggregation; Alkyltriphenylphosphonium bromides; Ammonium bromides; aqueous solutions; Atomic properties; Binding; Bromides; Bromides - chemistry; Carbon; Magnetic Resonance Spectroscopy; Micelles; Models, Molecular; molecular weight; Organophosphorus Compounds - chemistry; Potentiometry; Quaternary Ammonium Compounds - chemistry; Solubility; Solubilization; Solution; Surface-Active Agents - chemistry; Surfactants; X-radiation
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2011.10.074

[Display omitted] ► Micellization of surfactants with phosphonium and ammonium head group is compared. ► Solubilization and micellization capacity monotonously change with alkyl chain length. ► Surface tension isotherms and counterion binding differ for low and high homologues. ► Krafft temperatures for phosphonium series are lower compared to ammonium series. ► Solubilization capacity of phosphonium series is higher compared to that of ammonium series. A systematic study of the aggregation behavior of alkyltriphenylphosphonium bromides (TPPB-n; n=8, 10, 12, 14, 16, 18; here n is the number of carbon atoms in alkyl groups) in aqueous solutions has been carried out and compared with trimethyl ammonium bromides (TMAB-n). Critical micelle concentrations (cmcs) of TPPB-n and TMAB-n decrease with the number of carbon atoms with the slope parameter of ca.0.3. The low cmcs and effective solubilization power toward Orange OT indicate high micellization capacity of phosphonium surfactants. The low counterion binding parameter β is revealed for TPPB-10 and TPPB-12, while high counterion binding of ⩾80% is observed for high TPPB-n homologs. Values of the surface potential ψ calculated on the basis of pKa shifts of p-nitrophenols is similar for both series and monotonously increase with alkyl chain length. Several points indicate non-monotonic changes within TPPB-n series. There are peculiarities of the tensiometry and solubilization plots for high homologs and above mentioned increases in counterion binding on transiting from low to high molecular weight surfactants. Differences in aggregation behavior between TPPB and TMAB series and between low and high homologs can be due to the specific structural character of the TPP+ cation, which is supported by X-ray data.