Mechanical and structural properties of helical and non-helical silica nanowire

Energetically favorable configurations of silica nanowires with helical and non-helical structures and diameters ranging from 0.4 to 1.5 nm were obtained by using the simulated annealing basing-hopping (SABH) method with penalty function in our previous work. Those nanowires include five non-helical (2MR, 2MR-2O, 3MR-3O, 4MR-4O, and 5MR-5O) and three helical structures (4MR-3f, 4MR-4f, and 4MR-5f). In this study, their mechanical properties and structural characteristics were carried out by molecular dynamics simulation, specifically the temperature and diameter effect on the tensile strength, yielding strain, and Young's modulus. Results show that diameter significantly affects Young's modulus and yielding stress, whereas the temperature mainly influences yielding strain and yielding stress. The elastic deformation allows the variation of θO-Si-O to be about >16°. For comparison and insight, the mechanical property and deformation behaviors in the tensile loading are compared to those in the compression loading. Buckle deformation was observed on both helical and non-helical nanowires under the compression process, demonstrating that the nanowires exhibit a higher yielding strain and Young's modulus in the compression loading than in the tensile loading. In both the tensile and compression tests, the helical angle structures of silica nanowires lower the yielding strain and only slightly affect the yielding stress and Young's modulus.