Effect of Headgroup Variation on the Self-Assembly of Cationic Surfactants with Sulfonatocalix[6]arene

• Published in: Langmuir Vol. 33; no. 32; pp. 8052 - 8061
• Main Authors: Wintgens, Véronique, Harangozó, József G, Miskolczy, Zsombor, Guigner, Jean-Michel, Amiel, Catherine, Biczók, László
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 15.08.2017
• ISSN: 0743-7463; 1520-5827
• DOI: 10.1021/acs.langmuir.7b01941

The effect of headgroup variation on the association of supramolecular amphiphiles composed of 4-sulfonatocalix[6]­arene (SCX6) and cationic surfactant possessing tetradecyl substituent was studied in aqueous solutions at pH 7. When the surfactant contained hydrophilic trimethylammonium, pyridinium, or 1-methylimidazolium headgroup, highly reversible temperature-responsive nanoparticle–supramolecular micelle transformation could be attained at appropriately chosen component mixing ratios and NaCl concentrations. In these cases, the substantial negative molar heat capacity change (ΔC p ) rendered nanoparticle formation strongly endothermic at low temperature, whereas the assembly to supramolecular micelle was always accompanied by enthalpy gain. The ΔC p values became less negative when the charge density and the hydrophilic character of the surfactant headgroup diminished. The association of the more hydrophobic 6-methoxyquinolinium and quinolinium surfactants with SCX6 did not lead to supramolecular micelle formation because the self-assembly into nanoparticles was highly exothermic.