Reversible photorheological fluids based on spiropyran-doped reverse micelles

Area of Science:

• Materials Science
• Rheology
• Photochemistry

Background:

• Traditional fluids lack dynamic tunability.
• Controlling fluid properties with external stimuli is highly desirable.
• Photoresponsive materials offer potential for dynamic control.

Purpose of the Study:

• To develop a novel photorheological (PR) fluid with light-tunable rheological properties.
• To investigate the reversible viscosity changes induced by light in a lecithin/sodium deoxycholate (SDC) system doped with spiropyran (SP).
• To establish a simple and reproducible method for creating switchable fluids.

Main Methods:

• Formulation of reverse micelles using lecithin and sodium deoxycholate (SDC).
• Doping the SDC reverse micelles with a photochromic spiropyran (SP) compound.
• Characterization of rheological properties (viscosity) under UV irradiation and upon removal of UV light.

Main Results:

• The lecithin/SDC/SP mixtures exhibited high viscoelasticity due to long, wormlike reverse micelles.
• UV irradiation induced isomerization of SP to merocyanine (MC), causing a 10-fold decrease in viscosity.
• Upon removal of UV light, MC reverted to SP, and viscosity was fully recovered, demonstrating reversibility.
• The fluid response was repeatable over multiple cycles without significant loss.

Conclusions:

• A new class of simple, reversible photorheological (PR) fluids was successfully developed.
• The reversible viscosity change is attributed to light-induced alterations in the length of reverse micelles.
• This work presents the first example of a straightforward, reversible PR fluid using commercially available components.