Conformational Freedom‐Enhanced Optomechanical Energy Conversion Efficiency in Bulk Azo‐Polyimides

Abstract

Azobenzene-doped glassy polyimides (azo-polyimides) offer some of the most efficient optomechanical power densities to date rivaling electrostrictive polymers. Despite such potential attributes, the optomechanical efficiency remains low in comparison to other smart materials. Using high-fidelity coarse-grained molecular dynamics simulations, the authors reconcile both experimental and theoretical challenges to understand the limiting factors for the optomechanical conversion in photostrictive polymers. Interestingly, the ideal optomechanical efficiency of 10-24% for a single-chain azo-imide monomer predicted here is equal to or a little higher than experimental reports, suggesting experimental design space. The time-dependent optomechanical efficiency of bulk azo-polyimide is quantified, for the first time, to be strongly correlated with the initial free volumes, a measure of polymer conformational freedom. This trend is elaborated by conformational order parameters and viscoelastic relaxation moduli. Resembling the role of porosity in azobenzene-contained metal/covalent organic frameworks to enhance the photo-switching efficiency, a larger conformational freedom enables >10 times increase in optomechanical efficiency comparing to existing experiments. This is primarily due to facilitated viscoelastic relaxation after photo-switching which alleviates residual stresses quickly and reduces heat dissipation. These findings suggest opportunities to improve the optomechanical performance through targeted strategies, such as porosity control and thermal annealing.

The Impact of Foaming Effect on the Physical and Mechanical Properties of Foam Glasses with Molecular-Level Insights

“…MD simulations are effective tools [ 18 , 19 , 20 , 21 ] for probing the material structures and behaviors in an especially small spatiotemporal scale that is beyond the reach of conventional experimental facilities. Considering that carbon as a foaming agent is still superior to dextrin and the mixture of carbon and dextrin, in terms of product strength [ 17 ], we performed MD simulations (details in Materials and Methods) to elucidate our chosen optimal amount of carbon (i.e., 1 wt.%) [ 17 ] with molecular-level insights into the mechanism.…”

Probing the alignment-dependent mechanical behaviors and time-evolutional aligning process of collagen scaffolds

“…13,17,30,31 This CG model was used to characterize multiple properties, e.g., tension, 13,14,17,21,27,29,32 shear, 13,27 compression, 27 and cross-link-related properties 17,21 of COL molecules and bundles. These properties for macromolecules 33 are conventionally challenging to be simulated via all-atomistic (AA) models, necessitating the general development of CG models [34][35][36][37] for polymers, which effectively and reasonably handle the task in a predictive and versatile manner. This CG model is derived from a higher-fidelity AA triple helical tropocollagen model, which is generated from Protein Data Bank entry 3HR2 type I COL, 38 in order to access larger time and length scales (see ESI † for full details).…”