Light-Triggered Rheological Changes in a System of Cationic Wormlike Micelles Formulated with a Photoacid Generator

Abstract

“Smart” fluids displaying large changes in their rheological properties in response to external stimuli have been of great interest in recent years. For example, “smart” wormlike micelles (WLMs) that respond to pH can be readily formulated by combining a cationic surfactant such as cetyltrimethylammonium bromide (CTAB) with an aromatic compound such as 1,2-dihydroxybenzene (DHB). Here, we show that a pH-responsive aqueous formulation as mentioned above can be simultaneously made responsive to ultraviolet (UV) light by incorporating a photoacid generator (PAG) into the system. A commercially available PAG, diphenyliodonium-2-carboxylate, is used here. Upon exposure to UV light, this PAG irreversibly photolyzes into iodobenzene (IB) and benzoic acid (BA), with the formation of BA, leading to a drop in pH. WLMs formed by mixtures of CTAB, DHB, and the PAG are systematically characterized before and after UV irradiation. As the PAG photolyzes, an increase in the viscosity of WLMs occurs by a factor of 1000. We show that the ratio of the zero-shear viscosity η0 (after UV/before UV) depends on the initial pH of the sample. The UV-induced increase in η0 can be attributed to the growth of WLMs in solution, which in turn is influenced by both the ionization state of DHB and the presence of IB and BA.

Performance Evaluation and Formation Mechanism of Viscoelastic Surfactant Fracturing Fluids with Moderate Interfacial Activity Enhanced by Janus-SiO2 Nanoparticles

“…The higher G ″ than G ′ in low frequency indicates the dominated viscous behavior. In high frequency, G ″ is lower than G ′, and the dominant elasticity of solution reflects the solidlike behavior . The crossover frequency of G ′ (ω) and G ″ (ω) is determined as the critical angular frequency (ω c ).…”

“…In high frequency, G″ is lower than G′, and the dominant elasticity of solution reflects the solidlike behavior. 40 The crossover frequency of G′ (ω) and G″ (ω) is determined as the critical angular frequency (ω c ). Then, τ R can be calculated by eq 3 22 (3)…”

Unusual Increasing Viscoelasticity of Wormlike Micelles Composed of Imidazolium Gemini Surfactants with Temperature

“…1−4 These wormlike micelles usually entangle each other to form a transient network that imparts viscoelasticity to the solution. 5,6 The physical interactions among the wormlike micelles constantly break and reform, changing with the temperature and solution composition. 7−9 The change of the viscoelasticity of wormlike micelles with temperature has many advantages, such as the ease of temperature control and adjustment without the need for additives and easy preparation according to the change of the solubility of the surfactant at different temperatures or different interfacial activities.…”

“…Wormlike micelles are long, cylindrical aggregates of surfactants, which have aroused great interest among scientists over the past 20 years due to their widespread use in industry and daily life. − These wormlike micelles usually entangle each other to form a transient network that imparts viscoelasticity to the solution. , The physical interactions among the wormlike micelles constantly break and reform, changing with the temperature and solution composition. − The change of the viscoelasticity of wormlike micelles with temperature has many advantages, such as the ease of temperature control and adjustment without the need for additives and easy preparation according to the change of the solubility of the surfactant at different temperatures or different interfacial activities. Normally, with increasing temperature, the mean micellar length of wormlike micelles exponentially decreases .…”

Effect of the Substituent Position on the Phase Behavior and Photoresponsive Dynamic Behavior of Mixed Systems of a Gemini Surfactant and trans-Methoxy Sodium Cinnamates

“…Stimuli-responsive self-assemblies formed by surfactants or amphiphilic polymers in solutions have engaged wide interests primarily because their macroscopic physicochemical properties and microstructures have momentary and great changes in response to various stimuli including light, , redox reaction, , magnetic field, , temperature, , sound, , pH change, − or combined stimuli. , Self-assemblies with controllable responsivity have potential applications in various fields including hydrogel materials, , catalysis, drug delivery, − biosensors, perfume in personal care products, and especially soft templates with controllable structures for the synthesis of nanometer materials with various morphologies . Among them, the applications of stimuli-responsive vesicles and wormlike micelles were most widely studied.…”