Molecular Dynamics simulation of electrical field induced conformational transition and associated frictional performance of monomolecular films
X Ma and P Shrotriya, JOURNAL OF PHYSICS D-APPLIED PHYSICS, 45, 375306 (2012).
Sparse monomolecular film assemblies with polar end groups such as carboxyl have attracted considerable interest because of their ability to undergo conformational transition under electrical fields. We report the results from molecular dynamics simulation of electrical field induced conformational transitions and associated frictional performance of carboxyl-terminated monomolecular films. Simulation results indicate that the density of the monomolecular film has a significant influence on the conformational transition under electrical fields. In the case of loose-packed monomolecular films, carboxyl-terminated chains cluster together to form a disordered film due to large interchain separation. Under the application of a positive electrical field, the chain backbone rotates and lies down on the substrate forming disordered clusters, whereas under the application of negative electrical fields, the chains stand up and cluster together to form disordered clusters. Under shallow indentation with a purely repulsive indenter, loose-packed monomolecular films subjected to a positive electrical field exhibit a lower level of frictional response compared with films subjected to negative and no electrical fields. In the case of close-packed monomolecular films, the molecular chains assemble in an ordered film and the space is not enough for backbone chains to generate large-scale conformational transition. Due to this spatial limitation, the applied electrical field was not found to have any influence on the backbone chain rotation and associated frictional response under shallow indentations with a purely repulsive indenter.
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