Molecular Dynamics Study on the Photothermal Actuation of a Glassy Photoresponsive Polymer Reinforced with Gold Nanoparticles with Size Effect

Abstract

We investigated the optical and thermal actuation behavior of densely cross-linked photoresponsive polymer (PRP) and polymer nanocomposites containing gold nanoparticles (PRP/Au) using all-atom molecular dynamics (MD) simulations. The modeled molecular structures contain a large number of photoreactive mesogens with linear orientation. Flexible side chains are interconnected through covalent bonds under periodic boundary conditions. A switchable dihedral potential was applied on a diazene moiety to describe the photochemical trans-to-cis isomerization. To quantify the photoinduced molecular reorientation and its effect on the macroscopic actuation of the neat PRP and PRP/Au materials, we characterized the photostrain and other material properties including elastic stiffness and thermal stability according to the photoisomerization ratio of the reactive groups. We particularly examined the effect of nanoparticle size on the photothermal actuation by varying the diameter of the nanofiller (10-20 Å) under the same volume fraction of 1.62%. The results indicated that the insertion of the gold nanoparticles enlarges the photostrain of the material while enhancing its mechanical stiffness and thermal stability. When the diameter of the nanoparticle reaches a size similar to or smaller than the length of the mesogen, the interfacial energy between the nanofiller and the surrounding polymer matrix does not significantly affect the alignment of the mesogens, but rather the adsorption energy at the interface generates a stable interphase layer. Hence, these improvements were more effective as the size of the gold nanoparticle decreased. The present findings suggest a wider analysis of the nanofiller-reinforced PRP composites and could be a guide for the mechanical design of the PRP actuator system.

Do Columns of Azobenzene Stars Disassemble under Light Illumination?

“…The azo groups then remain stable in their newly assigned isomerization state at normal temperature. This model is adequate for our applications and has previously been successfully applied in a number of azobenzene-related studies. ,,,− …”

Light‐Responsive Inorganic Biomaterials for Biomedical Applications

“…[62] Composites of AuBNs and thermal-responsive polymers are accessible materials to fabricate light-controlled actuators and artificial muscle. [63,64] Doping AuNRs into UV-visible responsive azobenzene liquid-crystalline showed the proof-of-concept of a light-responsive soft robot by demonstrating the biomimetic motion of push-ups and sit-ups. [63] The photomechanical effects of the soft robot were achieved by two types of photoresponsive molecular motion-photothermally induced phase transition and trans-cis photoisomerization of azobenzene mesogens.…”

Cyclic Photoisomerization of Azobenzene in Atomistic Simulations: Modeling the Effect of Light on Columnar Aggregates of Azo Stars

“…Thus, switching between the trans and cis geometry of azobenzene can be incorporated. Out of multiple reported MD implementations of the photoisomerization reaction [39,42,43,[66][67][68][69][70][71][72][73], we employ the model of Heinz et al [42]. It has been used in various other simulation works [39,42,[73][74][75][76][77] and is consistent with the most important features of the isomerization of azobenzene.…”

“…Out of multiple reported MD implementations of the photoisomerization reaction [39,42,43,[66][67][68][69][70][71][72][73], we employ the model of Heinz et al [42]. It has been used in various other simulation works [39,42,[73][74][75][76][77] and is consistent with the most important features of the isomerization of azobenzene. Furthermore, the model is directly compatible with a range of force fields, among them the DREIDING force field employed in this study.…”