Photoresponsive Structured Liquids Enabled by Molecular Recognition at Liquid–Liquid Interfaces

Abstract

Using host−guest molecular recognition at the oil−water interface, a new type of photoresponsive nanoparticle surfactant (NPS) was designed and prepared to structure liquids. With the help of a polymeric surfactant, the interfacial host−guest interactions can be significantly enhanced, leading to the rapid formation and assembly of a NP monolayer and offering sufficient binding energy to hold the NPs in a jammed state. The assembly of the NPSs can be reversibly manipulated via a photoswitchable jamming-to-unjamming transition, endowing the interface as well as the macroscopic assemblies with responsiveness to the external trigger (photons). This study for the first time opens a pathway for the construction of multiresponsive, structured all-liquid systems by introducing host−guest chemistry, showing promising potential applications in encapsulation, delivery systems, and unique microfluidic devices.

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] .…”

Interfacial Synthesis: Morphology, Structure, and Properties of Interfacial Formations in Liquid–Liquid Systems

“…Controlled self-assembly of surfactant NPs synthesized at the liquid-liquid interface is now one of the most actively developed areas of research. The most attractive and promising topic is the creation of liquid dissipative structures, i.e., "3D printing of liquid in liquid" [9,68,70,[172][173][174][175]. The idea can be illustrated by the following example.…”

“…Based on "host-guest" molecular recognition at the oil-water interface, a photoreactive surfactant of nanoparticles was synthesized for fluid structuring. The assembly of nanoparticles can be reversibly changed by external action [174].…”

“…Fully liquid systems can be used in biology, catalysis, chemical separation [173], encapsulation, drug delivery systems, and microfluidic devices [174].…”

Recent Advances of Photoresponsive Supramolecular Switches

“…In the latest case, Shi and co-workers designed a lightregulated nanoparticle surfactant ( Figure 20) formed at the oilwater interface comprising the water-dispersible α-CD-modified gold nanoparticles (α-CD-Au-NPs) and the hydrophobic polymers of azo derivative. [92] Because of the host-guest interaction, a NPs monolayer was rapidly formed and assemble at oil-water interface and hold in a jammed state. Upon the UV light (365 nm) irradiation, the jammed state would transform into the unjammed state, which is accompanied by the change of droplet shape.…”