Influence of internal structure on properties and morphology of nanofiber textiles

P. Ryšánek, P. Čapková, O. Benada, M. Syrový

Faculty of Science, J. E. Purkyně University, České mládeže 8, 400 96 Ústí nad Labem

Our previous results showed that crystallization in the strong electric field, especially in case of wire spinning affects the crystal structure and phase composition of nanofibers. In any case the crystal structure is strongly affected by the preferred orientation of crystallites. The texture is typical fiber texture with cylindrical symmetry of distribution function of crystallites orientation. Fiber axis is in polymer chain axis and all the crystallographic planes, which are not parallel with texture axis, are suppressed in XRD powder diagram. This makes the structure and phase analysis very difficult. Anyway the profile analysis of diffraction pattern showed clearly that electrospinning changed the phase composition especially in case of wire spinning.

In present work we have found two special cases: PAN and PVDF, where the specific crystal phase in electrospun nanofibers significantly affected the fiber morphology and properties. In both cases electrospinning led to dominant crystal phase, that is characterized by two common features: (1) layered arrangement of chains in crystal structure and (2) charge polarity and electroactivity of these layers, as one can see in the figure 1. Both of these effects lead to the flat shape of crystalline fibers in the form of thin strips, which due to their flexibility and charge distribution roll up into tubes - forming hollow fibers. This work showed that hollow nanofibers can be prepared in a simple way and thus produce a nanofibrous membrane with a higher surface for further chemical modifications, respectively to improve the sound-insulating properties of the membranes.

(a) (b)

Figure 1: Illustration of charge distribution in polymer chains for PAN (a) and PVDF (b) in upper left corner (a) and (b). Charges were calculated in Materials Studio modeling environment. In the upper right corner of the images is the top view of one layer of polymer chains. Below are two perpendicular side views of the layered structures PAN (a) and PVDF (b).

The authors acknowledge the assistance provided by the Research Infrastructure NanoEnviCz, supported by the Ministry of Education, Youth and Sports of the Czech Republic under the project No.: LM2015073, and by project ERDF/ESF "UniQSurf - Centre of biointerfaces and hybrid functional materials" (No. CZ.02.1.01/0.0/0.0/17_048/0007411).

Student grant project of Internal Grant Agency SGS UJEP: Nanofiber Membranes for Specific Functions, No: UJEP-SGS-2019-53-006-3 is also acknowledged.