2. А.Э. Аринштейн. Size-dependent behavior of electrospun polymer nanofibers under small deformation

12 апреля 2022 года состоялось второе заседание общероссийского междисциплинарного научного семинара "Реология, вязкоупругость, ползучесть, пластичность и разрушение: эффекты, материалы, испытания, модели, анализ, технологии" С докладом "Size-dependent behavior of electrospun polymer nanofibers under small deformation" выступил Arkadii Arinstein, Technion – Israel Institute of Technology, Haifa 32000, Israel Аннотация Polymer materials of reduced size, such as thin films, and polymer nanofibers exhibit exceptional mechanical properties compared to their bulk samples. In particular, they demonstrate so-called size-dependent behaviour, a well-known phenomenon when the size and shape of nano-objects affect their mechanical and thermodynamic properties. For example, the elastic moduli of electrospun polymer nanofibers below a certain fiber diameter sharply increase with decrease in fiber diameters1. It turned out that, contradicting earlier suggestion, these unique properties cannot be explained by the contribution of surface energy. For example, the surface tension has no influence on Young’s modulus of electrospun polymer nanofibers demonstrating the size-dependent behaviour2. To clarify the impact of nanofiber internal structure, the experimental examining was done that has shown that no dramatic changes in polymer nanofiber internal structure occurs with variation in their diameter. According to X-ray analysis, only a mild, monotonous increase was observed in the crystallinity and orientation of the nanofibers as a function of their diameter1. Nowadays the concept that the above size-dependent behaviour of nano-objects is related to the confinement of supermolecular structures in polymer matrix, caused by the shrinking of their size, is common accepted3. The further progress in the examining and understanding of the problem in question requires an understanding of a mechanism of the confinement effect which provides the size-dependent elastic modulus of electrospun polymer nanofibers. For this goal the model based on following assumptions, was proposed: the nanofiber polymer matrix contains anisotropic regions consisting of correlated worm-like subchains, partially oriented along the fiber; a fiber elongation is accompanied by relative rotations of the above regions; confinement effect is that these rotations are hindered by the fiber boundary. As a result of the above restriction, the elastic modulus depends on the fiber diameter, in doing so the restriction is dominant for the thin fibers, is decreasing with increase of the fiber diameter, and becomes negligible for thick fibers4. The above anisotropic regions being a specific kind of supermolecular structure, are forming during electrospinning process when the polymer solution undergoes extreme high and rapid stretching accompanying by its heterogenization of polymer topological network5,6. References. 1. A. Arinstein, M. Burman, O. Gendelman, E. Zussman. Nature Nanotechnology, 2007, 2, 59. 2. M. Burman, A. Arinstein, E. Zussman. Europhysics Letters, 2011, 96, 16006. 3. A. Arinstein, E. Zussman. Journal of Polymer Science Part B: Polymer Physics, 2011, 49, 691. 4. A. Arinstein. Journal of Polymer Science Part B: Polymer Physics, 2013, 51, 756. 5. I. Greenfeld, A. Arinstein, K. Fezzaa, M. Rafailovich, and E Zussman. Physical Review E 2011, 84, 041806. 6. V. G. Kulichikhin, Al. Ya. Malkin, Al. V. Semakov, I. Yu. Skvortsov and A. Arinstein. European Physical Journal E 2014, 37, 10.