Piezoelectric property of hot pressed electrospun poly(γ-benzyl-α, L-glutamate) fibers

Abstract

Since the 1960s, the piezoelectricity in biopolymers (e.g. proteins and polynucleotides) has attracted considerable scientific attention. In particular, poly(glutamate)s have been one of the most popular targets for this research due to their well-defined helical structure and permanent polarity along the helical axis. To date, films of poly(glutamate)s have been shown to exhibit piezoelectricity only in shear mode (d 14 ), mainly due to the limitation in fabricating electrically poled polymer samples. This paper describes a combined electrospinning and hot press method that allows production of poled poly(γ -benzyl-α,Lglutamate) (PBLG) films with piezoelectricity in all d 33 , d 31 and d 14 modes for the first time. It is found that this PBLG film belongs to the matrix structure of C ∞v group, which is the same as that of poled PVDF film. The moderately high piezoelectric coefficients in both d 33 and d 14 modes as well as their thermal stability make the poled PBLG film an excellent candidate for use in flexible transducers and small energy harvesting devices.

Planar microphone based on piezoelectric electrospun poly(γ-benzyl-α,L-glutamate) nanofibers

“…12 The piezoelectricity was stable at 100 C for more than 24 h; this, to the best of our knowledge, is one of the highest thermally stable piezoelectric coefficient reported for poled polymers. 12 The fibers can be hot pressed at 100 C into continuous film without loss of piezoelectricity. The thermal stability, strong permanent dipole, and ease of fabrication make the PBLG-based piezoelectric fibers and film an excellent candidate for simple planar piezoelectric transducers, especially for potential use as underwater microphone and vector sensors.…”

“…45 to the fiber direction as previously described 12 and glued to a Mylar film to create diaphragm structure. Compared with the Mylar film, the PBLG film features a smaller dimension, and it is held by the microphone holder only at two opposing ends of the film and not on its entire periphery.…”

“…11 The fibers showed relatively large piezoelectricity: Compressive piezoelectric coefficient (d 33 ) of 20 pC/N and shear piezoelectric coefficient (d 14 ) of À1 pC/N. 12 The piezoelectricity was stable at 100 C for more than 24 h; this, to the best of our knowledge, is one of the highest thermally stable piezoelectric coefficient reported for poled polymers. 12 The fibers can be hot pressed at 100 C into continuous film without loss of piezoelectricity.…”

“…It was loaded on a hot press machine, Wabash G30H-15-BP (Wabash, IN), and 1000 lb stress was applied for 30 min at 100 C. 12 The microphone test sample was prepared by cutting the resulting film (15 lm) along the shear direction (45 to fiber direction) in a rectangular shape (see Fig. 5b in Ref.…”

“…5b in Ref. 12) and coating both the top and bottom surfaces with evaporated Al. This film (4 mm  19 mm) was attached to a Mylar film (25 lm thicknesses and 25.4 mm diameter) only by its two opposing sides of long axis to create a diaphragm structure which produces shear stress (d 14 ) to the PBLG molecules when deformed.…”