Temperature-Induced Critical Phenomenon of Hybrid Surfactant As Revealed by Viscosity Measurements

We have recently found that sodium 1-oxo-1-[4-(tridecafluorohexyl)phenyl]-2-hexanesulfonate (FC6-HC4), one of the synthesized hybrid surfactants that have both fluorocarbon chain and hydrocarbon chain in the molecule, exhibits a thermoresponsive viscoelastic behavior in aqueous solution. The aim of this study is to examine the viscosity behavior in solution of synthesized surfactants with different chemical structures (different lengths of fluorocarbon and hydrocarbon chains) as a function of temperature and to analyze the data obtained by using a theory of probability. The study reveals the importance of the chemical structure in which the numbers of carbon atoms are 6 and 4 in the fluorocarbon and hydrocarbon chains, respectively, for the hybrid surfactant to show the thermoresponsive viscoelastic behavior. This behavior is also found to be observed during the process where the size of assemblies of surfactant molecules decreases with rising temperature and when the probability of collision is highest between small and large molecular assemblies.