Potassium Phthalic Acid Research Articles

Design of pH-responsive “on-off” emulsions using CTAB/PPA emulsifiers by simulations and experiments

The pH-induced demulsification behaviors of “on-off” oil-in-water emulsions using cetyltrimethylammonium bromide (CTAB) and potassium phthalic acid (PPA) mixtures as emulsifiers were investigated by coarse-grained (CG) molecular dynamics (MD) simulations and experiments, aiming to design a new pH-responsive emulsion. On the one hand, we simulated the stability of emulsions of n-octane and aqueous CTAB/PPA solution, and phase diagrams of emulsion with different CTAB/PPA contents were observed at different pH. Furthermore, the demulsification processes from the low pH to high pH was investagated and clearly it began with film rupture and then accomplished with droplets fusion in few nanoseconds. Via analyzing the structure and molecular arrangment of the emulsion droplets, it was found that the reasons on pH-induced demulsification were weak hindrance effect of the surfactant film and electrostatic repulsion among emulsion droplets at high pH. On the other hand, through our experiments, the differences on stability of emulsions were verified and the reversible emulsification and demulsification processes by changing pH values were observed, which agreed well with our simulations. This work designed a new kind of pH-responsive emulsion using commercial surfactants CTAB/PPA by simulations and verified its pH-induced demulsification by experiments. It sets up a bridge between CG MD approach and experiment, which is expected to trigger further understanding and studies on stimuli responsive emulsion systems.

The pH and temperature dual-responsive micelle transition in the mixture of hydrotrope potassium phthalic acid and quaternary ammonium surfactants cetyltrimethylammonium bromide

ABSTRACTA facile and effective route to prepare a pH and temperature dual-responsive surfactant micelle has been introduced based on hydrotrope potassium phthalic acid (PPA) and quaternary ammonium surfactants cetyltrimethylammonium bromide (CTAB). The system can be switched between viscoelastic solution and water-like fluid by adjusting pH values. In this paper, different binding abilities between the hydrotrope and surfactants have been demonstrated during the process of adjusting pH because the hydrotrope has different ionization degrees with the pH variation. And with the aid of rheological measurements and cryo-TEM observation, we discussed the different effects of the hydrotrope on surfactants at various pH values in detail and analyzed the possible aggregate transition mechanism of CTAB–PPA system induced by pH. Besides, this CTAB–PPA system has temperature-responsive property when pH < 2.50. The temperature sensitivity and reversible control of rheological properties may greatly facilitate practical applications of such responsive viscoelastic solution.

Molecular insights into the pH-induced self-assembly of CTAB/PPA system

Self-assembly systems of stimuli-responsive molecules possess the capability of altering its morphologies and properties when receiving external signals (variations in pH value, temperature, light, etc), which has generated emerging applications, and therefore, attracted great interests. However, revealing mechanisms of stimuli-induced self-assembly morphology transition is still in its infancy and experimentally challenging. In this work, we studied the pH-induced self-assembly of cetyltrimethylammonium bromide (CTAB) and potassium phthalic acid (PPA) mixtures by coarse-grained (CG) molecular dynamics (MD) simulation, aiming to give insights into the pH-responsive self-assembly behavior. We simulated the self-assembly of CTAB/PPA mixtures, and obtained spherical, rod-like, and threadlike micelles depending on pH value and PPA/CTAB ratio. Besides, we found that the length of rod-like micelles fluctuated with the increase of PPA/CTAB ratio, and that the self-assembling morphology shifted between rod-like and threadlike micelles when fixing the PPA/CTAB ratio at 4:6 and varying the pH value. With analyzing the net charge number around the CTAB micelles, the arrangement and distribution of CTAB and PPA molecules in micelles, we concluded that the electrostatic shielding and space location-obstruct of PPA play a key role in the pH-induced self-assembly. This work revealed molecular-level information and mechanisms of the pH-induced self-assembly of CTAB/PPA mixtures, which is expected to trigger further understanding and studies on pH-responsive self-assembly behavior.

The influence of concentration and pH on the structure and rheology of cationic surfactant/hydrotrope structured fluids

Abstract In this paper, we show how to tailor the structure and rheology of aqueous solutions of the cationic surfactant cetyltrimethylammonium tosylate, CTAT, by adding a hydrotrope (potassium phthalic acid, PPA) or changing pH. Aqueous solutions of neat CTAT and CTAT/PPA binary mixtures were evaluated under different hydrotrope concentrations and compared with solutions of an analogous surfactant, cetyltrimethylammonium chloride (CTAC). PPA content promotes substantial increases in micellar flexibility and inter-micellar entanglements, resulting in a higher degree of structure in the fluid. Increasing the pH in neat CTAT leads to significant increases in low shear rate viscosities in comparison with CTAT at its original pH, because the OH ions favor surfactant aggregation as well as the growth of worm-like micelles. Nevertheless, increasing the pH in CTAT/PPA mixtures produced a progressive decrease in the low shear rate viscosities. This result is due to the nature of the interactions between CTAT and PPA, as well as to the ionization degree of the functional groups present in PPA. Cryo-TEM and 1 H NMR measurements evidenced, respectively, the microstructural and chemical environmental changes of CTAT upon PPA addition and explain the rheological properties of the CTAT/PPA mixtures as a function of the fluid structure.

Multi‐Responsive Wormlike Micelles Based on N‐alkyl‐N‐Methylpiperidinium Bromide Cationic Surfactant

AbstractA noncovalent bonding method was utilized for forming multiresponsive surface‐active ionic liquids in mixed N‐alkyl‐N‐methylpiperidinium bromide (C16MDB) and potassium phthalic acid (PPA). Rheology, cryogenic‐transmission electron microscopy, dynamic light scattering and nuclear magnetic resonance were used to investigate the aggregation property of surface‐active ionic liquids in aqueous solution. The efficiency of the shielding effect in the form of hydrophobic effects and electrostatic attraction between PPA and the C16MDB headgroup under diverse pH conditions is found to be the root cause of a shift in the aggregate's morphological transformation. In addition, the molecular motion of surfactant molecules becomes more active as the temperature increase provides the property of thermoresponsive to the surface‐active ionic liquid system.

Study of pH-responsive surface active ionic liquids: the formation of spherical and wormlike micelles

A noncovalent bonding method is utilized for forming pH-responsive surface active ionic liquids in mixed N-hexadecyl-N-methylpyrrolidinium bromide-based cationic surfactant (C16MPBr) and potassium phthalic acid (PPA). Rheology, cryogenic-transmission electron microscopy, and dynamic light scattering results revealed that the microstructure transition between spherical micelles and wormlike micelles was the fundamental cause of the pH-sensitive rheological properties. In addition, combined with nuclear magnetic resonance and UV–vis analysis, we found that the structure transition of micelles was attributed to different binding abilities of hydrotropes to C16MPBr as pH varies. It is confirmed that the binding ability of PPA to C16MPBr is strongest. This noncovalent bonding method is not only versatile but also economical for fabricating pH-responsive surface active ionic liquids.

Anion-Based pH Responsive Ionic Liquids: Design, Synthesis, and Reversible Self-Assembling Structural Changes in Aqueous Solution

The creation of pH responsive materials that undergo morphological transitions between micelle and vesicle induced by solution pH change is of great importance for their potential application in drug delivery and biochemical engineering. Here, we have developed a series of 18 pH responsive ionic liquids composed of 1-alkyl-3-methylimidazolium cation, [C(n)mim](+) (n = 4, 6, 8, 10, 12, 14), and different pH responsive anions such as potassium phthalic acid ([C6H4COOKCOO](-)), sodium sulfosalicylic acid ([C6H3OHCOOSO3Na](-)), and sodium m-carboxylbenzenesulfonate ([C6H4COOSO3Na](-)). The aggregation behavior and self-assembly structures of the ILs in aqueous solution have been investigated by surface tension, dynamic light scattering, transmission electron microscopy, small-angle X-ray scattering, and nuclear magnetic resonance spectroscopy. It was found for the first time that single tail ionic liquids, [C(n)mim]X (n = 12 and 14, X = [C6H4COOKCOO], [C6H3OHCOOSO3Na], and [C6H4COOSO3Na]) could form vesicles without any additives, and reversible transition was observed between spherical micelles and vesicles with the change of solution pH value. The transition in self-assembly structures is suggested to be driven by the variation in molecular structure and hydrophilicity/hydrophobicity of anions of the ILs.

A facile route to design pH-responsive viscoelastic wormlike micelles: Smart use of hydrotropes

A simple and effective route to design pH-responsive viscoelastic wormlike micelles based on commercial compounds is reported. According to this route, pH-sensitive viscoelastic fluids can be easily obtained by introducing a pH-responsive hydrotrope into a surfactant solution. In this paper, the mixed system of cetyltrimethylammonium bromide (CTAB) and potassium phthalic acid (PPA) was studied in detail. This pH-sensitive fluid can be switched between a gellike state and a waterlike state within a narrow pH change. Rheology and DLS results revealed that the pH-sensitive flowing behavior was attributed to the microstructure transition between wormlike micelles and short cylindrical micelles. Combined with fluorescence anisotropy, NMR, and UV–vis, it was demonstrated that the pH response of viscoelastic fluid originated from the different binding abilities of hydrotrope to surfactant as pH varies. Furthermore, different kinds of hydrotropes can be utilized to prepare pH-responsive viscoelastic fluids in the desired pH areas.