Photo-activated dynamic isomerization induced large density changes in liquid crystal polymers: A molecular dynamics...

Area of Science:

• Materials Science
• Polymer Chemistry
• Computational Physics

Background:

• Azo-mesogens in liquid crystal polymers exhibit light-induced density changes.
• The underlying physics of these dynamic trans-cis-trans isomerization cycles require further elucidation.

Purpose of the Study:

• To simulate and understand the physics of light-induced density changes in azo-mesogen-doped liquid crystal polymer networks.
• To investigate the relationship between isomerization dynamics and material density variations.

Main Methods:

• Molecular dynamics simulations were performed.
• Two simulation approaches were used: cyclic and probabilistic switching of isomers.
• Isomerization probabilities (trans-cis and cis-trans) were varied to mimic light intensity changes.

Main Results:

• Simulations confirmed that dynamic isomerization cycles cause density changes.
• The probabilistic switching approach explained the non-monotonous relationship between light intensity and density reduction.
• An optimal combination of isomerization probabilities was found to maximize density reduction, correlating with experimental findings.

Conclusions:

• Dynamic isomerization cycles of azo-mesogens in liquid crystal polymers are responsible for light-induced density changes.
• The frequency of these isomerization cycles critically influences the degree of polymer network distortion and subsequent density changes.
• Computational simulations provide a powerful tool for understanding complex photomechanical phenomena in materials.