Nanofiller‐Induced Enhancement of PVDF Electroactivity for Improved Sensing Performance

Abstract

Piezoelectric self‐powered sensors are promising platforms for wearable portable devices. Poly(vinylidene fluoride) (PVDF) and its copolymer derivatives are extensively explored as a soft piezoelectric material owing to their high piezoelectric coefficient, chemical thermal stability, biocompatibility, lightweight, and excellent flexibility. It is proved that the dominance of the electroactive (EA) β‐phase crystals versus the non‐electroactive α‐phase crystals is one of the key parameters to obtaining high piezoelectric performance of PVDF. Conventional methods, such as mechanical stretching, electrical poling, and high‐temperature annealing, are investigated to enhance the fraction of the β‐phase. Recently, embedding nanoscale fillers in the PVDF matrix has been investigated to further increase the β‐phase fraction and achieved considerable advances. The introduction of nanofillers is also advantageous in terms of improving the electrical conductivity and dielectric properties of PVDF, which are not readily obtained through conventional methods. This review introduces the principles of EA phase transformation in the presence of nanofillers and summarizes recent advances achieved by introducing various fillers, such as perovskites, oxide semiconductors, and 2D chalcogenides. The potential sensor applications of the PVDF nanocomposites responding to temperature, light, acoustic, and mechanical stimuli are reviewed. This review ends with the outlook of this new approach.

Enhanced capacitive pressure sensing performance by charge generation from filler movement in thin and flexible PVDF-GNP composite films

“…Depending on its specific application, PVDF can exhibit three distinct molecular conformations (TGTG’, TTT, and TTTGTTTG’) and manifest in five polymorphs, namely, phase 1 (beta (β)), phase 2 (alpha (α)), phase 3 (gamma (γ)), and δ, and ε phase. Of these, the β phase of PVDF is closely associated with the polarization charge magnitude due to its all-trans zig-zag conformation (TTT) [ 31 , 32 ]. This β phase can be induced through physical stress mechanisms such as stretching, quenching, straining, or polarization under a high electric field.…”

Flexible Composites for Piezocatalysis

“…The nanofillers act as nucleation sites for the formation of β‐phase crystals by interacting of groups of filler particles with the groups of the piezoelectric PVDF substrate to form a series of randomly distributed, tiny crystalline domains [22] . Surface charges or chemical bonds of the nanofillers can interact with the dipoles (−CF 2 −/−CH 2 −) of PVDF, so that these dipoles can self‐orient to the formation of β‐phase crystals with net dipole moments [23] . Despite the random distribution of nanofillers in the macroscopic scale, the above‐mentioned particle‐assisted crystallizing process occurs independently in each particle domain, and β‐phase forms in each domain under the microscope.…”

“…As a result, β‐phase of the PVDF increases at a macroscopic scale. Chatterjee et al [23] . reviewed the specific interaction mechanisms between the fillers and PVDF matrix for the formation of the electroactive β‐phase.…”

“…[22] Surface charges or chemical bonds of the nanofillers can interact with the dipoles (À CF 2 À /À CH 2 À ) of PVDF, so that these dipoles can self-orient to the formation of β-phase crystals with net dipole moments. [23] Despite the random distribution of nanofillers in the macroscopic scale, the above-mentioned particle-assisted crystallizing process occurs independently in each particle domain, and βphase forms in each domain under the microscope. As a result, β-phase of the PVDF increases at a macroscopic scale.…”

“…As a result, β-phase of the PVDF increases at a macroscopic scale. Chatterjee et al [23] reviewed the specific interaction mechanisms between the fillers and PVDF matrix for the formation of the electroactive β-phase. Electrostatic interactions and hydrogenbonding are the two driving forces accounted for the nucleation of β-phase.…”