Materials that change their shape upon exposure to light are attracting growing interest in applications such as soft robotics, microscale actuators, and smart materials. However, the connection between molecular-level structural changes and larger-scale deformation remains incompletely understood.

Tomomichi Itoh and his colleagues at Ehime University demonstrated that tiny light-induced structural changes within a polymer can be amplified into visible deformation of polymer microparticles. Their study revealed a hierarchical process that links molecular-scale events to shape changes in particles of several to tens of micrometers in size.

This research focused on azobenzene, a well-known light-responsive molecule that reversibly changes its shape under ultraviolet and visible light. Because of this unique property, azobenzene has been widely used in materials designed to respond to light.

Although azobenzene-driven deformation has been extensively studied in films and bulk materials, the processes occurring inside microscopic particles are not well understood. In particular, the structural pathway connecting molecular photoisomerization to particle-scale deformation remains unclear.

To investigate this, the researchers designed a polymer in which azobenzene units were incorporated directly into the main chain of the polymer. Using this material, they prepared polymer microparticles with diameters ranging from several micrometers to tens of micrometers.

Detailed analyses showed that light first changed the structure of the azobenzene units, followed by changes in the polymer chains and internal structure of the microparticles. These changes propagated through multiple structural levels and ultimately resulted in particle deformation.

This study established the following hierarchical pathway:

Azobenzene photoisomerization
↓
Polymer-chain rearrangement
↓
Reorganization of internal particle structure
↓
Microparticle deformation

The findings show how a molecular event can be translated into the deformation of an entire microparticle through a sequence of interconnected structural changes. This work provides a new design strategy for light-responsive microparticles, which may contribute to the development of light-driven micromachines, functional microparticles, and other advanced photoresponsive materials.