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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, γcmc, Гmax, and Amin 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. [ABSTRACT FROM AUTHOR]

A four-armed anionic star-shaped block polymer, containing an anionic polymer poly(2-Acrylamido-2-methylpropanesulfonic acid) (PAMPS) as the core group and poly(2-(Dimethylamino)ethyl methacrylate) (PDM) as the terminal group, was synthesized by using the Atom Transfer Radical Polymerization (ATRP) method. The (PAMPS50-PDM50)4aqueous solution exhibited both polyelectrolyte and hydrophobic associative characteristics, that is, a low concentration of NaCl results in decreasing viscosity but a high concentration of NaCl results in increasing viscosity. The four-armed anionic block polymer shows a CO2-reversible property at high concentrations of brine. Viscosity, pH, and ζ potential demonstrate the switchability jointly; the values could be switched from relatively low to high cyclically. These transitions could actually be attributed to the protonation of tertiary amine groups in PDM blocks, and the mechanism was proved by1H NMR. [ABSTRACT FROM PUBLISHER]

Here, we report a CO2stimulus-responsive system with anionic surfactant sodium oleate (NaOA) and N, N, N′, N′, N″-Pentamethyldipropylenetriamine (PMDPTA). The microstructure transition from spherical micelles to worm-like micelles was confirmed by rheology measurements, dynamic light scattering (DLS), and cryogenic transmission electron microscopy (Cyro-TEM). There were three types of CO2−responsive groups in PMDPTA. However, because of PMDPTA ionization degrees, just one responsive group of PMDPTA could be ionized by CO2to work with OA−, resulting in structure transformation from spherical micelles to worm-like micelles. Besides, this system could be switchable between low-viscosity fluid and high viscoelastic by CO2/N2. [ABSTRACT FROM AUTHOR]

The structure transitions of the aggregates in the sodium oleate (NaOA)/N-(3-(dimethylamino)propyl)-octanamide (DPOA) aqueous system was investigated upon CO2stimuli. During the process of bubbling of CO2, three appearance states of sol, gel, and emulsion with little white precipitate were observed continuously. The cryo-transmission electron microscope characterization and rheological measurements exhibited that the sol–gel transition was attributed to a spherical-wormlike micelle transition. Moreover, this transition was switchable at least three cycles in the pH range of 10.91–9.56 by CO2stimuli and pH regulation (adding NaOH), which could be explained by the protonation of DPOA and deprotonation of DPOA · H+. Bubbling of CO2resulted in protonation of DPOA, which not only inserted into the OA–as a co-surfactant but also screened the electrostatic repulsion among OA–, corporately leading to the spherical-wormlike micelle transition. Adding NaOH caused the deprotonation of DPOA · H+and hence reversed this transition. This surfactant system with switchable micelle transition not only displays tremendous application potential in various fields but also is of key importance in cyclic utilization of surfactant. [ABSTRACT FROM PUBLISHER]