Skip to content

Light-Induced Structural Transformation of Polymers in Liquids

Polymers are used in a multiplicity of functions and range in structure and type. Most commonly when referring to polymers one may think of plastics or rubber. However, Szymon Wiktorowicz at the University of Helsinki uses lasers to selectively dissolve polymers to create transparent images in otherwise cloudy polymer solution.

Szymon, a doctoral student at the university, has successfully synthesized polymers that are photochemically active and dissolvable in water as well as in certain alcohols. This polymer chain includes azo compounds which account for its transformative behavior. When subject to a laser of 365-nm the semi-dissolved polymer transitions from the trans to cis forms via reversible photoisomerization. The trans to cis shifts occur across the whole polymer chain. This causes the polymer to dissolve completely leaving a distinguishable clear spot in an otherwise uniformly cloudy liquid.

The effect is not permanent but can last a matter of hours depending on the solvent type and concentration. Aqueous solutions have shown to have lower critical solution temperature (LCST) behaviors while the polymers exhibit upper critical solution temperature (UCST) transitions in alcohol solutions.
This study is monumental as drawing with light has been found effective on solid surfaces but never before accomplished within a liquid.