Studying Photomechanical Effects in Azobenzene-Polymer Systems: A Numerical Approach

Photonastic materials convert light into mechanical energy, mimicking how flowers and plants move in response to sunlight. This study focuses on polymeric photoactuators with potential applications in microfluidics, biomedicine, soft robotics, and light-driven motors. Using a multiscale approach, we investigate a polymer thin film containing photoactive molecules, specifically photochromes like azobenzene (AZ), embedded in a polybutadiene (PB) matrix through molecular dynamics (MD) simulations. Our initial aim is to examine the mutual influence between the AZ and the polymer, followed by a strategy to investigate the coupling between the photochemical reaction and the intramolecular relaxation of the polymer. For this, the photoreaction is simulated by switching between the potential energy surfaces of the ground and excited states, of the AZ during MD simulations, allowing the polymer chains to rearrange dynamically. Additionally, we examine the geometric and distance relationships between AZ and PB atoms to understand their local interactions. Finally, macroscopic properties, such as the density variation due to photoisomerisation and the viscoelastic modulus, are studied through modeling of multi-photochromic systems.