PVDF/fluorescent carbon dots electrospun nanofibers with synergistic dipole alignment and multifunctional sensing applications

The development of novel multifunctional materials has been attracting continuous attention in recent years. In this work, fluorescent carbon dots (CDs) with a designed quasi-molecular structure were introduced into poly-vinylidene fluoride (PVDF) nanofibers to realize electro-mechano-photoluminescence coupling effects. The N-H and O-H groups in the CDs formed hydrogen bonds with C-F groups in PVDF, which not only ensured the uniform arrangement of the CDs in the nanofiber matrix, but also facilitated the polarization of the PVDF. The beta phase in PVDF was improved from 80% to 86% by doping of the CDs. Moreover, due to the asymmetric molecular structure of the carbon dot, it possessed an intrinsic dipole moment of 4.62 Debye. The self-assembly of the CDs on the nanofibers with a similar energy-favorable conformation improved the long-range spatial ordering in the nanocomposite. The CDs could also act as working dipoles, and contributed to the piezoelectric output of the whole device. Under a repeated finger imparting, the output voltage was enhanced from 6 V of the pure PVDF to 15 V of the nanocomposite. Furthermore, the CDs endowed the fiber with fluorescence capacity. The composite nanofiber exhibited bright fluorescence with excellent homogeneity. Through monitoring of the fluorescent intensity, visualized strain sensing and information encryption could be realized, which showed high potential of the nanofiber as a multifunctional nanocomposite.