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Modeling and Motion Analysis of a Light-driven Nano Mobile Robot

Hosseini Lavasani, Mohammad | 2019

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 57199 (08)
  4. University: Sharif University of Technology
  5. Department: Mechanical Engineering
  6. Advisor(s): Meghdari, Ali; Nejat Pishkenari, Hossein
  7. Abstract:
  8. In recent years, various nanocars have been synthesized to provide controlled mechanical function, transport other nanoparticles, or enable bottom-up assembly capability. In this research, using molecular dynamics and quantum mechanics, the motion of nanoworm on the gold substrate was investigated. The incorporation of the azobenzene chromophore at the middle of the chassis allows for the potential motion of nanoworm by light as a source of external stimuli. The creators claimed that nanoworm could achieve controlled wormlike movement on gold substrate, which should be validated as the purpose of this research. In the first section, the movement of the p-carborane wheel on the gold surface was investigated, which has not been studied before. Several major wheel configurations on the substrate were determined, and the potential energy surface (PES) was calculated separately during translation and rotation. Utilizing these PESs, the probable motion mechanism of the p-carborane is predicted, indicating the wheels tend to slide rather than roll. Next, the motion of the p-carborane was simulated using molecular dynamics (MD). By raising the temperature, three different regimes of diffusive motion of “trapped in the crystal structure”, “short-range fluctuations”, and “continuous motion” may be observed, and a quantified parameter was proposed to distinguish these regimes. It was shown that the two PES and MD approaches are in good agreement and the rotation of p-carborane around the substrate's horizontal axis is more difficult than a sliding motion, while rotation around the vertical axis is easier and likely to occur even at low temperatures. In the second section, several thermally-driven nanocars similar to nanoworm were selected, and the effect of temperature, substrate crystalline direction, and chassis shape on their mobility was evaluated using molecular dynamics. It was observed that nanocars similar to the wheel have three main regimes on the gold substrate, which show non-Arrhenius behavior. Nanocars do not have noticeable motion for temperatures below 450 K; in this regard, there is a suitable consistency with experimental observations. Rotational motion of nanocars around an axis perpendicular to the gold surface initiates at higher temperatures relative to their pure translational motion; as a result, carborane-wheeled nanocars have less tendency to rotate and rather perform translational motion. Also, according to PES and experimental research, nanocar wheels do not tend to rotate around the axis of the chassis and slide in most temperatures. The simulation results indicate that rigid-body MD overestimates the diffusion coefficient and predicts less adsorption energy on the substrate than the classical method, both of which have been reported in previous studies. In the third section, the absorption spectra of nanoworm in gas and solution phases were investigated by density functional theory (DFT) and validated with experimental evidence. It was observed that the CAM-B3LYP functional has the best agreement with the experimental results. Then, the ground and excited states of the nanoworm were compared with the azobenzene which shows the isolated azobenzene PES can accurately describe the energy levels of the nanoworm chromophore. According to the PES-fitting methods, the two important terms of the force field, including the CNNC dihedral and the CNN angle of the azobenzene chromophore, were replaced with the PES obtained from the DFT to add the capability of photoisomerization to this field. The results show that the movement of the photoinduced nanoworm is diffusive like other thermally-driven nanocars, and there is no noticeable change in the motion regime by the absorption of light; Because the strong adsorption of the nanoworm to the substrate prevents the chromophore from bending the chassis, and the nanoworm cannot move controllably on the gold surface
  9. Keywords:
  10. Nanocar ; Azobenzene Compounds ; Molecular Dynamics ; Quantum Mechanics ; Nanoworm ; Azobenzene Molecular Motor ; Gold Substrate ; Carborane

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