PH-Induced hydrogels and viscoelastic solutions constructed by a Rosin-Based Pseudo-Gemini surfactant

Abstract

• A novel pseudo-Gemini surfactant was constructed by mixing a rosin-based surfactant (C 10 MPAN) with maleic acid (MA). • Hydrogels at pH 5.35–5.00, 2.00 ∼ 1.00 and viscoelastic solutions at pH 5.00–2.00 are formed in the C 10 MPAN/MA system. • Vesicles, wormlike and enormous lamellar micelles were sequentially formed by decreasing the pH of C 10 MPAN/MA system. • In C 10 MPAN/MA system, maltese crosses lamellar liquid crystal was formed in the hydrogels at pH 1.00. Rosin-based surfactants exhibit unique superiority in self-assembly; however, pseudo-Gemini surfactants derived from rosin are rare. Herein, A new pH-responsive surfactant, N-decyl-maleimidepimaric acid N, N-dimethylenediamide (C 10 MPAN) was synthesized from rosin, and its structure was characterized by NMR and MS. Additionally, a novel pseudo-Gemini surfactant was prepared by mixing C 10 MPAN and maleic acid (MA) at a molar ratio of 2:1. Hydrogels at pH 5.35–5.00, viscoelastic solutions at pH 5.00–2.00, and hydrogels at pH ≤ 2.00 formed sequentially in the C 10 MPAN/MA aqueous solutions. The properties of these hydrogels and viscoelastic solutions were investigated using rheology, cryogenic transmission electron microscopy (cryo-TEM), differential scanning calorimetry (DSC), polarized optical microscopy (POM), and small-angle x-ray scattering (SAXS). The aggregates in the C 10 MPAN/MA aqueous solution underwent a transition from unilamellar vesicles to multilamellar vesicles, to wormlike micelles, and finally to enormous lamellar micelles as the pH was decreased from 5.35 to 1.00. The exponent between the zero-shear viscosity of the wormlike micelles and concentration reached 23.1. The sizes of the unilamellar vesicles at pH 5.35 varied from 10 to 100 nm, while those of the multilamellar vesicles at pH 5.00 reached 500 nm. Moreover, a Maltese crosses liquid crystal phase was formed by the lamellar micelles. 1 H NMR and surface tension methods were further used to investigate the aggregation mechanism induced by the pH. The large rigid skeleton of rosin acts as the backbone for the formation of diverse aggregates. This study shows the superior properties of rigid groups in the self-assembly of surfactants and provides a new insight for the applications of rosin.