Light-Triggered Reversible Control of Viscoelasticity and Emulsion Stability via Photoswitchable Aqueous Systems

Area of Science:

• Soft Matter Physics
• Materials Science
• Supramolecular Chemistry

Background:

• Intelligent soft materials rely on stimulus-responsive platforms like emulsions and gels.
• Reversible light-controlled modulation of macroscopic properties in these materials remains a significant challenge.

Purpose of the Study:

• To develop a multicomponent aqueous formulation for robust and reversible light-controlled modulation of viscoelasticity and emulsion stability.
• To investigate the coupling of molecular photoisomerization with macroscopic flow and phase behavior.

Main Methods:

• Formulation of a multicomponent aqueous system including cetyltrimethylammonium bromide (CTAB), cosurfactants, oil, water, and para-aminoazobenzene (AAB).
• Investigation of the system's behavior at different water contents under UV and visible light irradiation.
• Analysis of changes in viscoelasticity and emulsion stability through light-induced molecular rearrangements.

Main Results:

• A defined composition window yielded entangled wormlike micelles, creating gel-like viscoelasticity.
• UV irradiation disrupted the micellar network, drastically reducing viscosity; visible light restored it.
• At higher water content, stable oil-in-water emulsions were formed, with integrity reversibly controlled by light-induced interfacial changes.

Conclusions:

• The study demonstrates a simple and general strategy for light-controlled macroscopic properties in soft materials.
• This dual-level responsiveness opens avenues for adaptive formulations, reconfigurable soft matter, and light-controlled delivery systems.