Tiny molecular changes, big microparticle deformation
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.
Researchers from Ehime University have discovered a fascinating link between microscopic molecular changes and larger-scale deformations in polymer particles, as detailed in a recent study published in the journal Macromolecules. The study focused on azobenzene, a light-responsive molecule known for its ability to undergo reversible shape changes when exposed to ultraviolet and visible light.
Traditionally, azobenzene-driven deformation has been observed in films and bulk materials. However, the researchers sought to understand how these molecular events translate into visible deformations in microscopic particles, typically ranging from several micrometers to tens of micrometers in size. To investigate this, they created a polymer with azobenzene units incorporated directly into its main chain.
Using this specially designed polymer, the team prepared microparticles and observed the sequence of events leading to their deformation. The analysis revealed a clear hierarchical pathway: first, the photoisomerization of azobenzene units in the polymer; second, rearrangement of the polymer chains; third, reorganization of the internal structure of the particles; and finally, the deformation of the microparticles themselves.
This hierarchical process demonstrates how a molecular-level event—specifically, the photoisomerization of azobenzene—can cascade through multiple structural levels within a particle, culminating in noticeable shape changes. The findings not only clarify the mechanisms behind microparticle deformation but also open up new possibilities for designing light-responsive microparticles. These could be used in various advanced applications, such as micromachines, functional microparticles, and other photoresponsive materials.
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