Significant Electromechanical Characteristic Enhancement of Coaxial Electrospinning Core-Shell Fibers

Abstract

Electrospinning is a low-cost and straightforward method for producing various types of polymers in micro/nanofiber form. Among the various types of polymers, electrospun piezoelectric polymers have many potential applications. In this study, a new type of functional microfiber composed of poly(γ-benzyl-α,L-glutamate) (PBLG) and poly(vinylidene fluoride) (PVDF) with significantly enhanced electromechanical properties has been reported. Recently reported electrospun PBLG fibers exhibit polarity along the axial direction, while electrospun PVDF fibers have the highest net dipole moment in the transverse direction. Hence, a combination of PBLG and PVDF as a core-shell structure has been investigated in the present work. On polarization under a high voltage, enhancement in the net dipole moment in each material and the intramolecular conformation was observed. The piezoelectric coefficient of the electrospun PBLG/PVDF core-shell fibers was measured to be up to 68 pC N^-1 (d₃₃), and the voltage generation under longitudinal extension was 400 mVpp (peak-to-peak) at a frequency of 60 Hz, which is better than that of the electrospun homopolymer fibers. Such new types of functional materials can be used in various applications, such as sensors, actuators, smart materials, implantable biosensors, biomedical engineering devices, and energy harvesting devices.

Keywords: PBLG; PVDF; core–shell fibers; electromechanical transducer; electrospinning; energy harvesting devices; implantable biosensors; piezoelectric fibers.

Figure 1

The orientation of the dipole moment (red arrows) in (a) an electrospun PVDF fiber and (b) an electrospun PBLG fiber. The net dipole moment reveals the largest polar direction in which the piezoelectric coefficient of a material is the largest.

Figure 2

Schematic principle of fabrication of PBLG/PVDF core–shell fibers by electrospinning. The core solution is PBLG/DCM, the shell solution is PVDF/DMF–acetone. The external voltage (E) is from 16 to 20 kV.

Figure 3

Exploded view of the coaxial nozzle, reprinted from NanoNC Ltd.

Figure 4

(a) The SEM micrograph of electrospun PBLG/PVDF fibers and (b) the core–shell structure.

Figure 5

The SHG microscopy image of electrospun PBLG/PVDF fibers. The main red fiber is the core PBLG with a highly oriented dipole moment. The blurred red region is partially PVDF and/or a small amount of PBLG.

Figure 6

Experimental setup to measure the piezoelectric coefficients (a) d₃₃ and (b) d₁₃.

Figure 7

(a) The graph of the d₃₃ coefficient with the fitting line. The R² value is 0.9533. (b) The graph of the d₁₃ coefficient with the fitting line. The R² value is 0.9612.

Figure 8

The voltage measured under bending force to the coaxial PBLG/PVDF fibers at different frequencies: (a) pulse signal at 20 Hz, (b) 20 Hz, (c) 40 Hz, and (d) 60 Hz.

Figure 9

The force applied (a) by a sine shape form along the fiber axes and (b) charge generation in time domain.