PREPARATION AND CHARACTERIZATION OF PZT/PVDF COMPOSITES

FILMS FABRICATED BY ELECTROSPINNING METHOD

Do Phuong Anh1,*, Do Viet On1, Dao Anh Quang2, Nguyen Van Thinh3, Nguyen Thi Anh Tuyet4,

Vo Thanh Tung1 and Truong Van Chuong1

1University of Sciences, Hue University, Vietnam2Institute of Reasearch and Development, Duy Tan University, Danang, Vietnam3University of Technology and Education, University of Danang, Vietnam4Faculty of Natural Sciences, Quy Nhon University, Binhdinh, Vietnam

E-mail: dpasophys@gmail.com; vttung@hueuni.edu.vn

Abstract

In this paper, we present some properties of Lead Zirconate Titanate/Poly(Vinylidene Fluoride)

(PZT/PVDF) composites. The obtained results indicate that 0.9÷1.8 µm PZT/PVDF fibers involved

films were achieved using electrospinning method. In other hand, the effect of grain size, content and

other factors under the purview of Young’s modulus and ferroelectric properties.

Keywords: PVDF, PZT, composites, electrospinning, ferroelectric, piezoelectric, nanofiber.

1. Introduction

The use of ceramic nanoparticles in various organic polymers may provide performance and

multifunctional materials with applications in many technological fields such as actuators, sensors,

solar cells, optoelectronic devices, etc.

Polyvinylidene fluoride (PVDF) is a fluorinated polymer with excellent mechanical and electric

properties, which it was chosen as matrix due to their applications in a wide range of industrial fields.

Research in the field of material science and engineering has been devoted to the development of

innovative materials known as ceramic-polymer composites [2, 3, 8, 9, 13, 15, 16, 19-23, 25, 38]

Poly(vinylidene fluoride) (PVDF) is one of the semicrystalline polymers with at least five

crystalline phases, its can form a different crystal depending on the condition of the crystallization.

The different crystal structures are nonpolar α-phase, polar β -, γ -, δ- phase and ε – phase [4, 9, 12,

14-16, 18, 21, 25, 27-30, 35, 37, 39 ]. The β - phase crystal has all trans conformation that results in

the most polar phase among other crystals, being used extensively in piezoelectric, pyroelectric and

ferroelectric applications, because its piezoelectric activity is based on the dipole orientation within

the crystalline phase.

A variety of experimental techniques have been developed to induce β-phase formation in PVDF.

For example, Matsushige and Takemura showed that crystallization from the melt at pressures which

exceed 350 MPa led to the formation of the β-form of PVDF. Uniaxial or biaxial drawing of PVDF

mailto:dpasophys@gmail.com

films has also been shown to induce an α-β transition. In addition, a number of reports also indicate

that nanoclays, carbon nanotubes, graphene oxides and metal oxides can induce the β-crystal

formation in PVDF nanocomposites prepared via melt processing or solution processing. Besides,

electrospinning also produces pre-dominantly the β-phase.

Ceramic-polymer composites are studied regarding possible preparation procedures, their

ferroelectric properties and their tensile behavior. Furthermore, different arrangements of functional

ingredients are investigated such as 1-3, 2-2 and 0-3 composites [1-6, 11, 18-21, 26, 29, 31- 34, 38,

40].

Especially composites with ceramic fillers randomly dispersed in a polymer matrix are broadly

studied because of good preparation opportunities in order to vary the filler content, the filler and the

matrix materials. Such composites are called 0-3 composites according to Newnham’s connectivity

notation. Then, the PZT ceramic particles with excellent piezoelectric properties were evenly

dispersed in a three-dimensional connected flexible polymer matrix. This type of composite has

excellent comprehensive properties

The influence of preparation processes on the structure and electrical properties of piezoelectric lead

zirconate titanate/poly(vinylidene fluoride) composites was investigated. Electrospinning method can

enhance obviously the ferroelectric, dielectric and piezoelectric properties of PZT/PVDF composites

by reducing the void in piezoelectric composites and decreasing the interface defect between ceramic

phase and polymer phase [4, 5, 8, 10, 36, 40].

2. Experimental section

2.1 Materials

The PVDF used was Aldrich chemistry (France), average Mw~534,000. The solvents used were N,N-

dimethylformamide (DMF, Merck 99.5%) and acetone (Merck, 99.7%). The PZT ceramic (d33 = 317

pC/N, ɛr = 1800), which was prepared via the conventional solid-state reaction method, PZT powers

are prepared with a mortar and pestle, the mean particle size of the PZT powders is about 200 – 500

nm (Figure 1).

Figure 1. SEM images of particle size of the PZT before and after grinding

2.2 Devices

The crystalline structure analysis was performed at room temperature using an X-ray diffraction

system (XRD, Bruker D8 Advance, Germany) with Cu Kα radiation (λ= 0.154 nm) and Fourier

transform infrared (FTIR, Prestige 21 Shimadzu, Japan, Department of Chemical, Hue University of

Education) spectroscopy, respectively. The surface morphology was examined using a scanning

electron microscopy (SEM, Nova NanoSEM 450-FEI) operated at an accelerating voltage of 10–20

kV), the Raman spectra was recorded by a Micro Raman Spectrophotometer (JASCO Raman NRS-

3000) using 633 nm excited laser at room temperature. The polarization-electric field (P−E) hysteresis

loops were measured with a HIOKI 3532 (Radiant Technologies) which testing unit connected with

a high-voltage interface. The electrospinning apparatus was assembled by Hue University of Science

(Vietnam); it consisted of a high-voltage power supply, an automated syringe pump (KDS101, KD

Scientific, USA) with speed from 1mL/h to 999 mL/h and a 10-mL syringe with a 25-gauge diameter

of needle (~0.5 mm); The high electric potential (EG = 0 ÷ 30 kV) and the stretching force (FG) applied

during electrospinning, a steel rotating (E-HUSC-01, Hue University of Science, Vietnam) with 1500

rpm mandrel was used as the collector

2.3. Process

Preparation of the PVDF sol solution: The PVDF precursor solutions 16 wt% were prepared by

dissolving the PVDF powder in 3:1 DMF/acetone solution. The solution was heated at 65oC in silicon

oil bath for 30 min to completely dissolve the polymer.

Table 1. Samples of PZT/PVDF

Samples Composite

compound ratio

ρ (g/cm3)

No. Name of

products

F16 PVDF 16 wt% + 0wt% PZT 1.7

F-P5 PVDF 16 wt% + 5wt% PZT 1.8

F-P10 PVDF 16 wt% + 10wt% PZT 2.1

F-P15 PVDF 16 wt% + 15wt% PZT 2.4

F-P20 PVDF 16 wt% + 20wt% PZT 2.8

F-P25 PVDF 16 wt% + 25wt% PZT 3.1

Fabrication of the PZT/PVDF composite films by electrospinning: The PZT, which was added to

the PVDF solutions at concentration of 5, 10, 15, 20, and 25wt%, respectively (Table 1).

Solubilization was carried out at 65℃ under ultrasound for 1 hour.

The solution flow rate was precisely maintained at 1.5 mL/h using the syringe pump. A 12-cm

distance and an applied voltage of 14 kV were maintained between the needle and the collector [19].

The PZT/PVDF thin films were deposited by spin coating the solution after 4 h on the silver

substrates at room temperature. The wet films were annealed at 135 °C for different durations in an

oven.

Besides on, these composite films was found that the number of particles increases with the

increase in the PZT volume fraction. There is a non-uniformity observed in particle size of the

samples due to the presence of different particle sizes of PZT. The SEM micrographs also reveals

that there is an increase in the reinforcement of PZT particles in the PVDF matrix which indicates

that there is a change in volume fraction, Fig 2 [18].

3. Results and discussion

3.1 Crystalline phase analysis

3.1.1 Surface morphology

Figure 2a show the SEM micrographs of bare PVDF and PVDF with different wt% PZT. Smooth and

bead-free solid fibres were obtained for all the samples. In order to estimate fibre size, the

nanostructural photos of the composites were analyzed using Lince software. The fibre size located

between 0.45 µm and 1.8 µm and gathered round the top of Gauss fitting plot.

The electrospinning parameters can be adjusted to control final PVDF fiber characteristics. One of

the important parameters to consider is molecular weight of PZT. Figure 2 (a-m) shows the SEM

micrographs and fiber diameter distribution of the various PVDF fibers at different PZT contents.

During this sintering process, PZT/PVDF nanofibers become less flexible. At a higher voltage, the

jet draws away more solution, which requires a higher flow rate to create a stable Taylor cone. Too

low of a flow rate creates a break in the jet as more solution collects on the tip causes excess solution

to fall to the ground.

Figure 2. SEM images and grain size distribution for PZT/PVDF composites with different PZT:

(a-b) 0 wt%, (c-d) 5 wt%, (e-f) 10 wt%, (g-h) 15 wt%, (i-k) 20 wt%, (l-m) 25 wt%.

Figure 2 shows, these structures were morphologically analyzed by scanning electron microscopy

(SEM) with 900÷1800 nm diameter of PZT/PVDF, these process were achieved by maximum PZT

the concentration (sign: F-P25), the spraying technique is not possible with higher PZT concentrations

of 25wt% .

The effect of the PZT content on the morphology and average diameters of the PZT/PVDF

nanofibers is shown in Fig. 2. To further understand the impact of PZT on PVDF, it had an average

diameter of 450 nm (see in Figure 5(a-b)). However, an increase in the PZT content resulted in the

formation of the gradual diameter of nanofibers increases. The diameter of nanofibers was

significantly larger than mean difficult in spray coating on thin film [11, 22]. The PZT doping will

significantly benefits the β-phase crystallization of PVDF composites and remnant polarization,

however, if the PZT-doping concentration is too high, will damage the film quality, increase the

thickness of film spin-coating, make the PZT/PVDF film break up [2]. A complete film can be

achieved with 25 wt% PZT contents. On other hand, PZT can effectively improve the piezoelectric

properties of PVDF.

3.1.2 FTIR, XRAY and RAMAN, Crystalline structure

Figure 3a shows the FTIR spectra of aligned electrospun PVDF fibers with different PZT contents

(0–25 wt%); here the enhancement of β phase (infrared band at 478, 510, 840, 1072, 1274, and 1404

cm-1) with increasing PZT content can be observed [6].

The FTIR spectrums of the nanofilms (Figure 3a), the absorption peaks at 1274, 1072 and 840 cm-

1 are typical vibration characteristics of crystalline β phase. It is notable that doping PZT into PVDF

has a distinctive effect of both enhancing the crystalline β phase and weakening the crystalline α

phase. This effect is closely related to the concentration of PZT. For the spectrum of higher PZT

concentrations doped PVDF, the crystalline β phase absorption bands at 1274, 1072 and 840 cm-1

improve compared with lower concentrations [1, 6, 9-14, 20, 22, 24-31, 37, 40].

In order to confirm the crystalline phase of the samples and the influence of PZT ceramic particles

in the polymer matrix an X-ray diffraction analysis was carried out in the range 10° to 70° as shown

in Fig. 3b. The PZT powder sample exhibits characteristic peaks observed at 2θ = 21.3°, 31.1°, 38.4°,

44.5°, 50.2°, 55.3°, and 64.7° corresponding to the planes with Miller indices of (001), (110), (111),

(200), (201), (211), (022). For PVDF films, the shoulder peak at the 2θ value of about 17.2° corresponds

to (020) and (110) planes of crystalline α phase and peak at 20.4° indicates the PVDF β-phase [1, 5,

6, 7, 11, 12, 16, 17, 20-31, 40].

Figure 3. FTIR spectra and XRD curves of the PZT/PVDF composite film with different wt% PZT

By comparing the PZT powder with of the PZT-PVDF composites, it is found that there is no

additional evidence of structural change, XRD analysis is in good agreement with FTIR analysis.

Figure 4. Raman spectrum of PVDF 16%wt with different contant of PZT

We prepared the 0-3 composites of pure PVDF and doped them with PZT the concentration (5-25

wt%). The PZT content was done to increase the conductivity of the matrix as this increased

conductivity will enhance the poling of ceramic at a later stage.

Figure 4 shows that the Raman spectra of the PZT-PVDF film are completely dominated by the

PZT material. The peaks with wave numbers of 130, 185, 374, 545 and 573 cm-1 were assigned to the

tetragonal PZT phase. These peaks are identified as A1(1TO), E(2TO), A1(2TO), E(3TO), and

A1(3TO) modes, respectively [6, 7, 12, 25, 26, 30, 40]. It has also been shown that when the PZT

increases several times, it is shown that the peak intensities are from 600 cm-1 to 1000 cm-1, most of

the PZT crystals have been trapped in the PVDF matrix during crystallization. This is clearly seen

through the SEM image of the composite.

Figure 5. Tensile stress-strain properties of PZT/PVDF nanofiber composite films prepared with

different levels of PZT content. The inset shows the results of Young’s modulus for PZT/PVDF

nanofiber composite films.

Figure 5 shows the typical stress/strain curves of all samples. The Young’s moduli of the

PZT/PVDF composite nanofibres were much higher than that of the bare PVDF nanofibre, especially

for the 15 wt% samples. A slight decline in mechanical properties for the 25 wt% sample may have

been due to its low crystallinity, as confirmed by the XRD and Raman spectrum results.

PZT doping will significantly benefits the β-phase crystallization of PVDF nanocomposites and

remnant polarization, however, if the PZT-doping concentration is too high, will damage the film

quality, increase the thickness of film spin-coating, make the film less transparent, warp the substrate,

and in the worst case, make the PZT/PVDF film peel off. This may have been due to the addition of

PZT hindering the movement of the PVDF molecular chain, which reduced the elasticity and the

elongation of the composite [9, 12, 17, 24, 39].

PZT can effectively improve the piezoelectric properties of PVDF, although excessive PZT doping

will limit the flexibility of composite film as it sustains less elongation just before failure. However,

it had been found that high doping concentrations will increased remnant polarization because there

will be a significant increase in the dielectric constant and thus the piezoelectric signal will increase

[12, 23].

3.2 Ferroelectric properties of the PZT/PVDF films

A series of P–E hysteresis loops for PZT/PVDF composite measured at room temperature were

shown in Fig. 6. The results showed that the composites with PZT volume fraction 5 to 25 wt%

exhibited non-saturated P–E hysteresis loop.

Figure 6. The P−E hysteresis loops for F16(a) and F16-x%PZT films with different concentrations

of PZT, x= 5 (b), 10 (c), 15 (d), 20 (e), 25 (f) wt%

It is also be noted that when increasing the PZT content to beyond, values of remnant polarization

increases and coercive field decreases to a finite value as shown in table 2. The results thus suggested

that distribution of PZT granules in PVDF matrix played a significant role in controlling of

ferroelectric behavior. The ferroelectric properties of the PZT/PVDF films with different

concentrations of PZT between 5 and 25 wt% were investigated.

Table 2. Ferroelectric properties of the PZT/GO/PVDF films

Samples Composite

compound

ratio

Remnant

Polariation

(Pr) µC/cm2

Coercive

field

(EC) kV/cmNo. Name of

products

F16 0 2.1 9.3

F-P5 5 4.3 7.2

F-P10 10 4.8 6.1

F-P15 15 5.3 6.1

F-P20 20 5.9 5.7

F-P25 25 6.2 4.8

The gradual increase of Pr is caused by the crystallinity enhancement of polar β-phase with

increasing of doped PZT and annealed techniques. The correlation between the amorphous phase

contents and ferroelectric properties of PZT thin films was further discussed from the viewpoint of

local chemical structures, Fig.6 [7, 17-21, 34, 35, 40].

A remnant polarization increasing from 2,1 to 6.2 mC/m2 were achieved by optimizing the concentration of 25 wt% of PZT, while simultaneously reducing the coercive field at the same time.

The modification of the physical properties can be explained by alterations in PVDF fiber due to

drawing and poling and to the presence of PZT (Table 2), [10, 36].

4. Conclusion

In this study, PZT-PVDF composites with 0–3 connectivity was successfully fabricated from a

series of PZT volume fractions from 5 to 25 by electrospinning method. With the increase of the PZT

content, an enhancement of the β phase was observed. The PZT-PVDF composites open new

opportunities to develop a large scale manufacturing of flexible devices, piezoelectric devices,

sensors, force transducer, and so on with technological applications.

Experimental density values of the composites were found to be harmonized with calculated

density values. SEM observations revealed a homogeneous mixture of PZT-PVDF phases. The values

of stress - strain coefficient and ferroelectric character obtained in this work revealed that it may be

more suitable for widely future applications.

Acknowledgements

This work was carried out in the framework of the National Project in Physics Program until 2020

under No. ÐTÐLCN.10/18.

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