The effect of macrocycle size on the association of supramolecular amphiphiles composed of 4-sulfonatocalix[n]arene and 1-methyl-3-tetradecylimidazolium (C14mim+) was studied in aqueous solutions at pH 7. When the cavitand contained four sulfonatophenol units (SCX4), spherical nanoparticle (NP) formation was observed. In contrast, both supramolecular micelle (SM) and NP formation could be attained in the presence of NaCl when the larger, more flexible 4-sulfonatocalix[8]arene (SCX8) served as host compound. The SCX8-promoted self-assembly into SM was enthalpically more favorable than NP production but the molar heat capacity changes in the two processes barely differed. Addition of 50 mM NaCl significantly increased the enthalpy of C14mim+−SCX8 NP formation making thereby the self-organization into SM more favorable. The transformation of SM into NP at high temperature was due to the substantial entropic contribution to the driving force of NP formation. The critical micelle concentration and the local polarity in the headgroup domain were considerably lower for SM compared to those of C14mim+Br conventional micelle
