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储晁倪
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1 UDC PVDF Fabrication and Induction Mechanism of Piezoelectric PVDF Micro/Nano-Fibrous Membranes by Electrospinning :

3 , PVDF

4 1. 2.

5 Polyvinylidene fluoride, PVDF PVDF αβγδ ε β PVDF β PVDF PVDF PVDF β FTIR-XRD PVDF β γ β PVDF Lambert-Beer Law Gregorio β Fβ 16 wt%v NMP /V acetone =2/8 ~ 6/4 β Fβ 95% 98.6% Fβ Fβ Fβ PVDF β β F(β) ~ 94.9% β β I

6 PVDF PVDF PVDF β PVDF β PVDF γ PVDF II

7 Abstract Abstract Polyvinylidene fluoride (PVDF), the only widely used as flexible piezoelectric material, presents the highest pieozoelectricity among all piezoelectric polymers. At least, five crystalline phases, i.e. α, β, γ, δ, and ε phases, are known to exist in PVDF. Among them, the β phase shows the best piezoelectric activity, which attracts people s interest. A process of stretching and the poling followed is thought to be the regular way to obtain the piezoelectric PVDF membranes. However, the traditional cold-drawing and high-temperature & strong electrical poling approach is difficult to achieve high-level β phase, and also complicated, time-consuming, resource-wasting, etc., which limits its application. Recent electrospinning technology has received great attention in fabricating piezoelectric PVDF membrances, because it combines stretching and electrical poling into single-step electrospinning process. In order to realize the preparation of high-performance piezoelectric PVDF membrances, the key issues, such as the influences of electrospinning parameters on the membranes and their crystalline phases, and the mechanism of electrospinning inducing piezoelectric β phase, should be addressed. This study concentrates on a few key issuses the above and conducts some intensive works as follows: The influences of key electrospinning parameters on electrospun PVDF membranes and their crystalline phases are systematically invesitaged. The method of Fourier Transformation Infrared (FTIR) in conjunction with X-Ray Diffraction (XRD) is adopted to analyse the membrane phases and the piezoelectric β and γ phases are successfully identified. The polymer solution concentration, solvent component and feeding rate are found to affect the fiber morphology and the phase greatly, and a close relationship is disclosed: the better the morphology is, the more remarkable the β phase becomes. Based on Lambert-Beer Law for the absorption of PVDF FTIR spectra and according to Gregorio equation, the fraction of β phase, F(β) is calculated and comparatively analyzed. Results show that the average F(β) value up to 95 % and the III

8 Fabrication and Induction Mechanism of Piezoelectric PVDF Micro/Nano-Fibrous Membranes by Electrospinning maximum 98.6% can be achieved at a solvent volume ratio of V NMP /V acetone =2/8 ~ 6/4 for the standand solution under the best processing parameters. A special relationship between the fiber diameter and F(β) is revealed, i. e. F(β) increases with decreasing diameter for reducing feeding rate when under the same concentration solutions; however, F(β) does not decrease with diameter increased in those higher concentration solutions when at the same flow rate. The electrospinning inducing β phase mechanism is revealed through the observation and analyses of the jet behaviors and the resultant fiber morphology during this process, and the investiagations of the forcespun fibers, spin-coated films and solution-cast films. A high F(β) of 94.9% is found in the forcespun fibers, (forcespinning with pure mechanical force but without electrical field ), and no β phase is observed in both spin-coated and solution-cast samples. Therefore, it confirms that the effective stretching of the jet is the fundamental reason for β phase induced in electrospun samples. The piezoelectric response of PVDF membranes is tested and the electric field during electrospinning is proved to play some role in orienting dipoles. Results show that only the electrospun fiber membranes show piezoelectricity among all unpoled PVDF samples, and the piezoelectric performance increases with increasing F(β). After poling, the piezoelectricity of β-phase PVDF fiber samples is further improved; however, the γ-phase samples still show very poor piezoelectricity. Keywords: electrospinning, polyvinylidene fluoride (PVDF), piezoelectric membrane, crystalline phase control, spectroscopic property IV

9 ... I Abstract...III PVDF PVDF PVDF PVDF PVDF PVDF PVDF V

10 PVDF PVDF PVDF PVDF FTIR XRD FTIR-XRD PVDF PVDF PVDF PVDF VI

11 5.2 PVDF PVDF PVDF PVDF VII

12 TABLE OF CONTENTS TABLE OF CONTENTS ABSTRACT...III CHAPTER I INTRODUCTION Piezoelectric Polymeric Membranes Piezoelectric Polymers Techniques for Preparing Polymeric Membranes Trends of Piezoelectric Polymer Membrane Development Piezoelectric PVDF Membranes Piezoelectric Phase Control in Electrospun PVDF Membranes Electrospinning Technique Polymorphic Phase Transformed during Electrospinning PVDF Research Objectives and Main Works...21 CHAPETER II PREPARATIONS AND CHARATERIZATIONS OF PVDF MEMBRANES Electrospun PVDF Membranes Fibers in Random Distribution Fibers in Aligned Arrangement Non-electrospun PVDF Membranes Force-spun Fiber Membranes Spin-coated Films Solution-cast Films Experimental Equipment and Materials Main Instruments Materials Characterizations of PVDF Membranes Concluding Remarks...32 VIII

13 Fabrication and Induction Mechanism of Piezoelectric PVDF Micro/Nano-Fibrous Membranes by Electrospinning CHAPTER III ELECTROSPUN PVDF MEMBRANES AND VAR- IATIONS OF CRYSTALLINE PHASE THEREOF Electrospinning Parameter Designs Morphologies of Electrospun Fibers Influence of Polymer Solution Parameters Influence of Processing Conditions Ambient Parameters Crystalline Phases in ELectrospun PVDF Membranes Introduction to PVDF Spectra FTIR Study of Electrospun PVDF Membranes XRD Study of ELectrospun PVDF Membranes Results of FTIR-XRD Intergrated Analyses Crystalline Phase Variation Rules in Electrospun PVDF Memberanes Concluding Remarks...64 CHAPTER IV DISCUSSION OF PIEZOELECTRIC PHASE IND- UCED IN ELECTROSPUN PVDF FIBER MEMBRANES Existing Theoretical Explanations Influences of Mechanical Stretching and Solution Crystallization on Crystalline Phases of PVDF Membranes Crystalline Phases of Forcespun PVDF Fiber Membranes Crystalline Phases of Spin-coated Films Crystalline Phases of Solution-cast Films Discussion and Summary Relationship between Jet Stretching and Piezoelectric β-phase Induced druing Electrospinning Process Jet Behaviors during ELectrospinning Process Induction Mechanism of Effective Jet Stretching Concluding Remarks...86 IX

14 TABLE OF CONTENTS CHAPTER V PIEZOELECTRICITY MEASUREMENT OF PVDF MEMBRANES Working Principles of Piezoelectric PVDF Membranes Fundamentals & Equation of Piezoelectricity Working Modes and Equivalent Circuit Introduction to Piezoelectricity Measurement of PVDF Membranes Pressure Dynamic Measurement System Fabrication of Piezoelectric Sensitive Membranes Piezoelectricity Measurement of PVDF Membranes Piezoelectricity of Electrospun PVDF Membranes Piezoelectricity of Non-electrospun PVDF Membranes Discussion and Summary Concluding Remarks CHAPTER VI CONCLUSIONS & PROSPECTS Summary of Works and Findings Future Prospects REFERENCES PUBLICATIONS ACKNOWLEDGMENTS X

15 [1-2] [3-5] 2070 [5-14] P. Curie J. Curie [15-18] K. Brain [19] 1965 P. HarrisF. E. AllisonG. Hauver [20-22] [23-28] DNA RNA [29] 1

16 PVDF 1969 H. Kawai [30] PVDF 1971 K. Nakamura PVDF [31] 80 Y. Higashihata PVDF-TrFE PVDF-TeFE [32-34] PVDF [35-36] VDCN [37-38] [39-40] PVDF PVDF : 1PVDFPTFEPVC PZT-PZT-PbTiO 3-2

國家圖書館典藏電子全文

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