Redox-Responsive, Reconfigurable All-Liquid Constructs

Abstract

Using host−guest chemistries in a biphasic system, a novel supramolecular nanoparticle surfactant (s-NPS) with redox-responsiveness is presented to structure liquids. The in situ assembly/jamming and disassembly/unjamming of s-NPSs at the oil−water interface are reversibly controlled by a switchable redox process, imparting a nanoscale redox-responsiveness, affecting the assemblies on all length scales. "Smart" all-liquid constructs including structured emulsions and programmable liquid devices are easily prepared, showing promising applications in responsive delivery, release, and reaction systems.

Phosphotungstate-Functionalized Mesoporous Janus Silica Nanosheets for Reaction-Controlled Pickering Interfacial Catalysis

“…Regulated by external stimuli, the JNS emulsifiers were convertible between surface-active and surface-inactive, enabling emulsification and demulsification in a controllable manner. Many external stimuli, such as CO 2 /N 2 , pH, redox state, temperature, and light irradiation, have been reported to regulate the surface activity of JNP materials. − However, the stimuli of CO 2 /N 2 , pH, and redox state are invasive, which often bring about some undesirable side effects in catalytic reactions. − Triggers such as temperature and light are noninvasive, but they are limited to small-scale operation (temperature changes are energy-intensive and time-consuming, and light has a limited penetration depth in reaction solution due to the opaqueness of emulsions). − In addition, such external stimuli modes required additional steps to regulate the stability of Pickering emulsions, which was unfavorable for energy-saving and sustainable industrial applications. If the emulsion characteristics can be controlled by the catalytic reaction process without any additives and additional energy input, that is, the emulsion is stable during the reaction, and quickly demulsified when the reaction is completed, these problems can be solved.…”

Responsive Interfacial Assemblies Based on Charge‐Transfer Interactions

“…With surfactants assembled at the interface, one liquid can be dispersed in another immiscible liquid to form emulsion droplets, which typically take spherical shapes to decrease the interfacial area and, therefore, to reduce the interfacial energy [5–8] . Recently, by using the electrostatic interactions or host–guest interactions between nanoparticles (NPs) dispersed in aqueous phase and polymeric/oligomeric ligands dissolved in oil phase to form nanoparticle surfactants (NPSs) at the oil–water interface, an alternate strategy is put forward to stabilize the oil–water interface [9–12] . Due to the self‐regulated number of ligands anchored to the NPs, the binding energy of the NPs can be significantly enhanced to withstand the compressive force exerted on the particles when the interfacial area decreases, allowing the stabilization of liquids in nonequilibrium shapes, i.e., structuring liquids [13–15] .…”

“…The reversible, dynamic noncovalent interactions between NPs and ligands play a crucial role in the formation of NPSs at the interface, not only endowing NPSs with self‐regulating properties to maximize the reduction in the interfacial energy, [26] but also giving the resultant liquid constructs reconfigurable properties in response to environmental stimuli, like pH, light, and redox [11–12, 27] . Among the various noncovalent interactions used to construct supramolecular systems, charge transfer (CT) interactions between electron‐rich donors and electron‐deficient acceptors have attracted extensive attention with regard to their optical and electronic properties [28–31] .…”

The Assembly and Jamming of Nanoparticle Surfactants at Liquid–Liquid Interfaces

“…Recently, a cooperative assembly strategy was put forward by using the noncovalent interactions between functionalized NPs dispersed in one liquid and polymeric ligands with complementary functionality dissolved in the second liquid [12–14] . “Janus‐like” nanoparticle surfactants (NPSs) form in situ at the interface, maximizing the reduction in the interfacial energy per particle and of the assembly, and generating an elastic NPS monolayer at the interface.…”