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Review
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Characterization and Application of PVDF and Its Copolymer Films Prepared by Spin-Coating and Langmuir-Blodgett Method

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Review

Characterization and Application of PVDF and Its Copolymer Films Prepared by Spin-Coating and Langmuir-Blodgett Method

Zerun Yin et al. Polymers (Basel).

Abstract

Poly(vinylidene fluoride) (PVDF) and its copolymers are key polymers, displaying properties such as flexibility and electroactive responses, including piezoelectricity, pyroelectricity, and ferroelectricity. In the past several years, they have been applied in numerous applications, such as memory, transducers, actuators, and energy harvesting and have shown thriving prospects in the ongoing research and commercialization process. The crystalline polymorphs of PVDF can present nonpolar α, ε phase and polar β, γ, and δ phases with different processing methods. The copolymers, such as poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), can crystallize directly into a phase analogous to the β phase of PVDF. Since the β phase shows the highest dipole moment among polar phases, many reproducible and efficient methods producing β-phase PVDF and its copolymer have been proposed. In this review, PVDF and its copolymer films prepared by spin-coating and Langmuir-Blodgett (LB) method are introduced, and relevant characterization techniques are highlighted. Finally, the development of memory, artificial synapses, and medical applications based on PVDF and its copolymers is elaborated.

Keywords: memory; organic ferroelectric polymers; poly(vinylidene fluoride); synapse.

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Three representative chain conformations of tg+tg for the α and δ phase, tttt for the β phase, and tttg+tttgfor γ and ε phase. Reproduced from [12], with permission from Springer Nature, 2012.
Figure 2
Figure 2
Approaches for obtaining the β phase of PVDF. From the melt, the α phase, or by solvent casting and adding fillers. Reproduced form [18], with permission from Elsevier, 2014.
Figure 3
Figure 3
Procedure of preparing PVDF-based solution: (a) weigh the solute; (b) add solvent and magnetic stir bar; (c) magnetic stirring; (d) a transparent and homogeneous solution is obtained. Adapted from [19], with permission from Springer Nature, 2018.
Figure 4
Figure 4
(a) Diagram of transferring monolayers to a solid substrate in the LB method; (b) measured isotherm of the surface pressure versus the remaining trough area while preparing pure PVDF LB films.
Figure 5
Figure 5
(a) FTIR absorbance spectra; (b) XRD diffractograms of PVDF membranes. Reproduced from [65], with permission from Royal Society of Chemistry, 2017.
Figure 6
Figure 6
Circuit for characterizing ferroelectric thin films: (a) I vs. t and I vs. V; (b) P vs. V; (c) C vs. V; (d) P vs. T; (e) I vs. T.
Figure 7
Figure 7
General process of polarization switching. Reproduced from [90], with permission from Springer Nature, 2014.
Figure 8
Figure 8
(a) Polarization switches uniformly without domain formation. (b) The thickness-dependent coercive field of P(VDF-TrFE). Reproduced from [84,118], with permission from American Physical Society, 2010 and 2000, respectively.
Figure 9
Figure 9
(a) Normalized P(E) hysteresis loop derived from Equation (9), with stable, metastable, and unstable states denoted in heavy, thin, and dotted lines, respectively. (b) Evolution of the normalized polarization over time and current during switching. Reproduced from [119], with permission from American Physical Society, 2003.
Figure 10
Figure 10
Memory taxonomy. Many emerging nonvolatile memories (NVMs) are in simple two-terminal devices and suitable for high-density crossbar arrays. Reproduced from [128], with permission from Elsevier, 2016. SRAM: static random access memory; DRAM: dynamic random access memory; PCM: phase change memory; MRAM: magnetic random access memory; STT-RAM: spin torque transfer random access memory; FeFET: ferroelectric field effect transistor; ReRAM: resistive random access memory; FTJ: ferroelectric tunneling junction.
Figure 11
Figure 11
Schematic of different ferroelectric memories: (a) polarization–voltage hysteresis of a metal–ferroelectric–metal (MFM) capacitor; (b) capacitance–voltage hysteresis of a metal–ferroelectric–insulator–semiconductor (MFIS) diode; (c) drain current–gate voltage hysteresis of FeFET; (d) conductance–voltage hysteresis of FTJ.
Figure 12
Figure 12
The ferroelectric memory cell of an MFM capacitor and transistor: (a) 1T1C (one-transistor–one-capacitor); (b) 2T2C (two-transistor–two-capacitor). BL (bit line), WL (word line), and PL (plate line).
Figure 13
Figure 13
FeFET with metal–ferroelectric–insulator–semiconductor (MFIS) structure: (a) schematic of the FeFET; (b) equivalent circuit model of the FeFET. The dotted square indicates the gate-to-channel region of the FeFET. Reproduced from [148], with permission from IOP publishing, 2017.
Figure 14
Figure 14
FTJ and multiferroic tunnel junction (MFTJ) based on PVDF or P(VDF-TrFE): (a) schematic of PVDF FTJs and the I–V curves in the 1- and 2-layer devices; (b) schematic of the MFTJ of LSMO/P(VDF-TrFE)/Co on SrTiO3 (STO) substrate and measured magneto-response curves. Reproduced from [5,157], with permission from Springer Nature, 2016 and American Chemical Society, 2018, respectively. TMR: tunnel magnetoresistance.
Figure 15
Figure 15
Characterizing the P(VDF-TrFE)-based nanogenerator: (a) the open-circuit voltage; (b) the short-circuit current; (c) equipment and connection for generating mechanical load to the nanogenerator.; and (d) analysis of stretching–releasing cycle. Reproduced from [201], with permission from Elsevier, 2014.

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