High solubility and viscoelastic properties of carboxylate surfactants with α-tert-butylphenoxy group

Carboxylate surfactants have excellent properties, including low irritancy and biocompatibility. However, the solubility of carboxylate surfactants is usually low at ambient temperatures, which limits their applications in many fields. Introducing a hydrophobic branch is an effective strategy to disrupt molecular packing, thereby enhancing solubility and promoting advanced self-assembly behavior. Herein, by introducing p-tert-butylphenoxy groups at the α-position of sodium laurate, sodium myristate, and sodium palmitate respectively, a series of carboxylate surfactants (abbreviated as C n -p-(t-bu)ph-Na, n = 12, 14, 16) were synthesized. These surfactants exhibit high water solubility and excellent self-assembly capability. Among them, C 12 -p-(t-bu)ph-Na achieved a solubility of 207.7   mmol∙L -1 at 25 °C, with Krafft points below room temperature. X-ray diffraction (XRD) analysis indicated that the bulky substituent induced a tilted, less compact molecular packing in the solid state. Surface tension measurements showed that the critical micelle concentration ( cmc ) was reduced by more than one order of magnitude compared to conventional carboxylates, with the surface tension at cmc ( γ cmc ) reduced to approximately 28 mN·m -1 . Rheological analysis and cryo-TEM confirmed that C 12 -p-(t-bu)ph-Na and C 14 -p-(t-bu)ph-Na formed entangled wormlike micelles without additives, imparting pronounced viscoelasticity. These findings establish rigid hydrophobic branching as a simple and effective design strategy for developing bio-based surfactants with tunable solubility and dynamic aggregation behaviors, offering new opportunities in controlled release, personal care, and advanced soft materials.