pH and temperature-responsive wormlike micelles formed by single amine oxide surfactant

ABSTRACT

In this paper, a novel type of pH- and temperature-responsive smart wormlike micelles based on (Z)-N,N-dimethyl-3-(octadec-9-enamido) propan-1-amine oxide (OAPAO) synthesized was studied. The structure of OAPAO was characterized by ¹H NMR and FTIR. The micellization and aggregation properties of the OAPAO surfactant in aqueous solution at different pH values were studied using equilibrium surface tension. The OAPAO solution exhibited pH-regulated surface activity at the air–water interface by assessing relevant parameters such as cmc, γ_cmc, Г_max, and A_min at pH = 2.10, 6.80, and 11.90. The viscosity and rheological measurements demonstrated the pH-sensitive flowing behavior and property, which was attributed to the interactions transition between the OAPAO head groups. Moreover, the system could be promptly switched between low viscous fluid and highly viscoelastic fluid by alternatively adjusting the pH between 2.05 and 6.82. Combining the distribution state of OAPAO, a mechanism for the different intermolecular forces at different pH regions was proposed. Furthermore, the OAPAO solution exhibited an evident temperature-responsiveness at pH = 6.82 and 11.88 in a certain temperature range (25–65°C) resulting from the effect of temperature on the hydrophobic effect and the intermicellar branching junctions.

GRAPHICAL ABSTRACT

KEYWORDS:

• Hydrogen bond
• hydrophobic effect
• pH and temperature responsive
• viscoelastic fluid