Contemporary Engineering Sciences, Vol. 11, 2018, no. 97, 4797 - 4808

HIKARI Ltd, www.m-hikari.com

https://doi.org/10.12988/ces.2018.89524

Characterization of the Piezoelectric Response of

Vinylidene Polyfluoride Reinforced with

Esmeraldine and Graphene

Lina Marcela Hoyos Palacio1, Edwin Espinel Blanco2,

Jesús Alberto Guaca Vera 3, Francisco Antonio León Villegas4

and Harold Alonso Ballesteros Ruiz5

1 Engineering, Energy and Thermodynamics, Dept. of Materials Science

Faculty of Engineering, Universidad Pontificia Bolivariana, Medellin, Colombia

2 Mechanical Engineering, Dept. of Mechanical Engineering

Faculty of Engineering, Universidad Francisco de Paula Santander Ocaña

Vía Acolsure, Sede el Algodonal Ocaña Norte de Santander, Colombia

3 Mechanical Engineer, Dept. of Mechanical Engineering, Faculty of Engineering

Universidad Francisco de Paula Santander Ocaña

Vía Acolsure, Sede el Algodonal Ocaña Norte de Santander, Colombia

4 Mechanical Engineer, Faculty of Engineering

Universidad Francisco de Paula Santander Ocaña

Vía Acolsure, Sede el Algodonal Ocaña Norte de Santander, Colombia

5 Mechanical Engineer, Dept. of Mechanical Engineering, Faculty of Engineering

Universidad Francisco de Paula Santander Ocaña

Vía Acolsure, Sede el Algodonal Ocaña Norte de Santander, Colombia

Copyright © 2018 Lina Marcela Hoyos Palacio et al. This article is distributed under the

Creative Commons Attribution License, which permits unrestricted use, distribution, and

reproduction in any medium provided the original work is properly cited.

Abstract

A mixture of reduced graphene oxide (rGO) with esmeraldine (rGO-Esmeraldine)

was used in order to modify the piezoelectric properties of vinylidene polyfluoride

(PVDF). PVDF films were prepared by dissolving PVDF powder in a solution of

N, N-Dimethylformamide (DMF), preheated at 60 ° C, to enhance the β phase of

4798 Lina Marcela Hoyos Palacio et al.

the PVDF, the phase responsible for the piezoelectric effect. The influence of the

r-GO-Esmeraldine mixture on the piezoelectric properties of the PVDF was

characterized by X-ray diffraction. Changes in piezoelectric potential were

observed by varying the mass percentage of the rGO-emeraldine mixture in the

PVDF films. The results show an increase in potential by adding 0.1 wt% and 0.3

wt% of the rGO-emeraldine mixture. At concentrations greater than 0.3wt% the

formation of the β phase in the PVDF is reduced due to the inhomogeneous

distribution of the rGO in the PVDF film and the crystallization thereof as a

consequence of the addition of esmeraldine that was evidenced by Scanning

Electron Microscopy (SEM).

Keywords: Graphene; esmeraldine; vinylidene polyfluoride; characterization;

piezoelectric potential

1. Introduction

Vinylidene polyfluoride (PVDF) is an important polymer that has piezoelectric

and ferroelectric properties and is widely used in many applications such as

electroacoustic transducer, pressure sensor and ferroelectric random access

memory, etc. There are mainly five crystalline phases of PVDF: α, β, γ, δ, and ε,

with the α and β phases which are the most common crystalline structures among

them [2, 3]. The α phase of the PVDF is the one with the trans and gauche

alternating stereochemical conformation, therefore, it is not polar and is generally

obtained when PVDF is cooled from the melted mass. The β phase is

characterized by a completely trans-flat zigzag conformation, with all the fluorine

atoms located on the same side of the polymer chain, so it is polar and makes a

great contribution to the piezoelectric and ferroelectric properties of PVDF[4, 5].

To date, a variety of approaches have been developed to induce β-phase formation

in PVDF. Among them, the incorporation of nanoparticles in PVDF is considered

one of the simplest forms, such as organically modified nanoclay, ferrite

nanoparticles, carbon nanotubes and graphene oxide, among others [6-10].

Graphene has attracted great attention due to its structure and superior electrical,

mechanical, optical and thermal properties [11-16]. In fact, graphene has a high

electrical mobility greater than 2 ∗ 105cm2V−1s−1 [17-18]. Due to its fascinating

properties, graphene appears as a promising material in numerous technological

applications [19, 20]. To fully exploit these properties, graphene can be

incorporated into polymer matrices. And for PVDF, graphene can serve as a

nucleating agent for the generation of the polar phase β, thanks to the specific

interactions between the large π bond in graphene and the high density fluorine

atoms in the PVDF. In addition, since graphene is conductive, the PVDF /

graphene compound has a higher dielectric constant than that of pure PVDF,

which can reduce the inverter voltage while maintaining high electromechanical

conversion coefficients when used as a pressure sensor.

Characterization of the piezoelectric response of … 4799

However, graphene is often difficult to disperse uniformly in the polymer matrix

because its sheets can easily be re-agglomerated or re-stacked in graphite due to

the strong van der Waals interactions between them. However, only promoting the

dispersion of graphene in the PVDF matrix can benefit the formation of β phase in

PVDF and improve the properties of PVDF / graphene. In order to make graphene

well compatible with polymers, appropriate functional groups have to be obtained

that allow it to interact with specific chemical residues in polymer matrices [21,

22]. The formation of the β phase in the PVDF is also favored by the solvent that

is used in the preparation thereof, the greater polarity the solvent has, the greater

the formation of the β phase that will be obtained, an example of a polar solvent is

dimethylformamide[23]. Some researchers have indicated that PVDF can be

modified by doping it with graphene to improve its thermoplastic properties [24,

1], ductility [25] and conductivity [26].

The active piezoelectric and pyroelectric phase with an orthorhombic unit cell in

Trans-Trans (TT) conformation can only be obtained after special processing,

since in this conformation fluorine and hydrogen atoms are on opposite sides of

the polymer backbone chain, forming a net dipole moment other than zero [1].

The high properties and benefits of graphene oxide (GO) have generated an active

area of research in which many investigations have shown possible applications in

various technological fields. Due to the highly hydrophilic nature of GO, an

aqueous colloidal suspension of graphene oxide nanolamines (GOn) can be easily

obtained by full exfoliation of bulk graphite oxide by simple sonication in water

[27]. For many practical reasons, the large scale preparation of graphene oxide

dispersions in organic solvents is highly desirable as this will further expand the

potential applications by facilitating the manufacture and practical use of

graphene or graphene oxide-based polymer nanocomposites [28].

Polyaniline is found within the conductive polymers, being this property highly

attractive for different applications. Of all the states of polyaniline, only the

emeraldine salt state exhibits a high electrical conductivity and is therefore

considered the doped state of the PANI. The remaining states (leucoemeraldine,

emeraldine base, pernigraniline base and salt) are electrical insulators. The

electrical conductivity of the PANI-ES is due to the high mobility of the load

carriers, in this case, hollows in the polyaniline chain.

In this work, the PVDF was reinforced with an rGO-emeraldine mixture to

enhance the piezoelectric property of this polymer. The materials developed were

characterized by means of DRX and SEM.

2. Experimental phase

2.1 Materials

PVDF Sigma-Aldrich Co, H2SO4 Merck 95-97%, HCl Merck 37%, HNO3 Merck

4800 Lina Marcela Hoyos Palacio et al.

65%, Aniline monomer Sigma-Aldrich Co, Graphite Bars Sealco, N, N-

Dimetilformamida Merck, Phenylhydrazine Chloride- Merck.

2.2 Preparation of the PVDF compound plus rGO-esmeraldine.

The rGO-esmeraldine mixture was disperse in Dimethylformamide solvent

(DMF) [5] (1 mg ml-1) and was sonicated for 4 hours at room temperature, the

PVDF powder was dissolved in DMF (80 mg ml-1) and stirred for 2 hours at a

temperature of 60 ºC, the rGO-esmeraldine mixture was added to the PVDF

solution and was stirred for 30 min at 60 ºC, subsequently this was sonicated for

10 min at room temperature and stirred again for 1 hour [25]. Then, it was placed

in a vacuum chamber for 45 min in order to eliminate the bubbles that were

formed in the stirring process. Once the bubbles were eliminated, the mixture was

placed in glass molds and then put in an oven for 24 hours at a temperature of

70ºC. The sheets of the developed compound have concentrations of 0%wt,

0.1wt%, 0.3wt%, 0.5wt% y 0.7wt% [29, 30].

2.2 Characterization

The sheets obtained during the process were characterized by means of the

following techniques: X-Ray Diffraction (XRD), using a Rigaku MiniFlex

diffractometer Cu Kα (λ=1.542 A) in the 2θ range from 5° to 90°; Scanning

Electron Microscopy (SEM) using a high vacuum JCM-6000PLUS equipment

with 15 kv drive voltage, 7.475 nA probe current, and a 0.3546 adjustment

coefficient.

3. Results and discussion

3.1. Dispersion of the rGO-esmeraldine mixture in the PVDF

The dispersion state of the rGO-emeraldine mixture was evaluated by SEM as

shown in fig. 1-4, where a good dispersion of the rGO-emeraldine mixture is

observed in small proportions of mass for the case of 0.1wt% because in mass

portions greater than this, a crystallization of the material is evidenced for the case

of 0.3wt% 0.5wt% and 0.7wt%.

Characterization of the piezoelectric response of … 4801

a) b)

c) d)

Figure 1. SEM image for the PVDF rGO-PANi mixture at a)0,1wt%. b) 0,3 wt%.

c) 0,5 wt%. d) 0,7 wt%. Source: The authors.

As shown in fig. 2-4, a crystallization of the material can be observed due to a

higher percentage in the addition of esmeraldine since it could be corroborated

that, as reported by the literature, the esmeraldine tends to crystalize the used

matrices to be reinforced with it unlike figure 1, which shows that the esmeraldine

in small quantities is well dispersed in the PVDF.

3.1. Formation of the β phase in the films obtained

The X-ray diffraction technique is a very useful method to determine the

crystalline phase in the developed sheets. Fig. 5-10 show the diffraction patterns

of the PVDF powder, the PVDF mixture and the rGO-esmeraldine in its different

concentrations 0wt%, 0,1wt% 0,3wt% 0,5wt% y 0,7wt%. Taking into account the

intensity of the main diffraction peaks in the phases α, where 2θ=18.271°, and β,

where 2θ=20.23° of the PVDF powder, the α/β relationship can be obtained in

order to determine the percentage of the β phase in the film obtained [5].

The eq. (1) shows the formula for determining the % of the β phase.

% β phase= (α/β PVDF powder- α/β PVDF-rGO-esmeraldine %) * 100

4802 Lina Marcela Hoyos Palacio et al.

The diffraction patterns show a greater formation of the β phase in the sheets with

a mass percentage of the rGO-esmeraldine mixture in the PVDF of 0wt%, 0,1wt%

and 0,3wt%.

Figure 2. RX diffraction patterns for the PVDF powder. Source: The authors.

Figure 3. RX diffraction patterns for the pre-heated PVDF at 60°C. Source: The

authors.

a) b)

Characterization of the piezoelectric response of … 4803

c) d)

Figure 4. RX diffraction patterns for the pre-heated PVDF at 60°C and

reinforced with rGO-esmeraldine a) 0,1wt%. b) 0,3wt%. c) 0,5wt%. d) 0,7wt%.

Source: The authors.

Table 1.

COMPOUND % β Phase

pre-heated PVDF at 60°C 49

PVDF Graphene-Pani 0.1% 55

PVDF Graphene -Pani 0.3% 51

PVDF Graphene -Pani 0.5% 38

PVDF Graphene -Pani 0.7% 35

Source: the authors.

Using eq. (1), the percentage of the formation of the β phase in the sheets

developed could be determined (phase responsible for the piezoelectric effect in

the PVDF); a greater percentage of the β phase was also observed in the PVDF

films mixed with rGO-esmeraldine at 0.1wt% and 0.3wt% as shown in table 1.

3.3. Potential difference obtained from the films with higher percentage in

the formation of the β phase.

Figure 5. Sheets obtained during the development of the Project. Source: The

authors.

4804 Lina Marcela Hoyos Palacio et al.

Two copper plates were used, which served as electrodes to measure the

piezoelectric response of the obtained material, using a multimeter.

Figure 6. Piezoelectric response of the PVDF compound plus rGO-esmeraldine at

0,3wt%. Source: The authors.

Figure 7. Piezoeletric response of the PVDF compound plus rGO-esmeraldine at

0,1wt%.

Source: The authors.

Values of 256 milivolts, for the PVDF sheet reinforced with rGO-esmeraldine at

0,3wt%, and 326 milivolts, for the PVDF sheet reiforced with rGO-esmeraldine at

0,1wt%, were obtained. These values were superior to the PVDF sheet with a

reinforcement percentage of 0,0 wt%, which showed a potential defference of 126

milivolts.

4. Conclusions

PVDF films were developed with different concentrations of rGO-esmeraldine,

which were prepared in a DMF solution preheated at 60ºC to ensure the formation

Characterization of the piezoelectric response of … 4805

of the β phase, which evidenced that the temperature preparation is fundamental

for the formation of this phase.

By means of the X-ray diffraction technique, a greater formation of the β phase

could be evidenced in the PVDF mixture with rGO-esmeraldine in concentrations

of 0.1wt% and 0.3wt%.

The images obtained by means of the SEM showed the crystallization of the

material obtained from the PVDF mixture with rGO-esmeraldine concentrations

higher than 0,1wt%, since the esmeraldine, according to the reported in the

literature, tends to crystallize the matrices used for its reinforcement. An increase

of the piezoelectric potential of the films using a percentage of the reinforcing of

0,1wt% and 0,3wt% was evidenced.

References

[1] M. El Achaby, F. Z. Arrakhiz, S. Vaudreuil, E. M. Essassi and A. Qaiss,

Piezoelectric  β-polymorph formation and properties enhancement in graphene

oxide - PVDF nanocomposite films, Appl. Surf. Sci., 258 (2012), no. 19, 7668–

7677. https://doi.org/10.1016/j.apsusc.2012.04.118

[2] A. Salimi and A. A. Yousefi, Analysis Method: FTIR studies of β -phase

crystal formation in stretched PVDF films, Polymer Testing, 22 (2003), 699–704.

https://doi.org/10.1016/s0142-9418(03)00003-5

[3] S. Mishra, K. T. Kumaran, R. Sivakumaran, S. P. Pandian and S. Kundu,

Synthesis of PVDF/CNT and their functionalized composites for studying their

electrical properties to analyze their applicability in actuation & sensing, Colloids

Surfaces A: Physicochem. Eng. Asp., 509 (2016), 684–696.

https://doi.org/10.1016/j.colsurfa.2016.09.007

[4] A. C. Lopes, C. M. Costa, C. J. Tavares, I. C. Neves and S. Lanceros-Mendez,

Nucleation of the Electroactive γ Phase and Enhancement of the Optical

Transparency in Low Filler Content Poly (vinylidene)/ Clay Nanocomposites, The

Journal of Physical Chemistry C, 115 (2011), 18076–18082.

https://doi.org/10.1021/jp204513w

[5] C. Arenas, D. Rangel, V. M. Castaño, E. Loa and M. Vega, Sensores

piezoeléctricos de fluoruro de polivinilideno modificado con nanopartículas de

sílice para aplicaciones en MEMS, Superf. y Vacío, 23 (2010), no. 3, 20–25.

[6] B. D. Shah, P. Maiti, E. Gunn, D. F. Schmidt, D. D. Jiang, C. A. Batt, E. P.

Giannelis, Dramatic Enhancements in Toughness of Polyvinylidene Fluoride

Nanocomposites via Nanoclay-Directed Crystal Structure and Morphology, Adva-

4806 Lina Marcela Hoyos Palacio et al.

nced Materials, 16 (2004), no. 14, 1173–1177.

https://doi.org/10.1002/adma.200306355

[7] P. Martins, C. M. Costa, M. Benelmekki, G. Botelho, and S. Lanceros-

Mendez, On the origin of the electroactive poly (vinylidene fluoride) β -phase

nucleation by ferrite nanoparticles via surface electrostatic interactions,

CrystEngComm, 14 (2012), 2807–2811. https://doi.org/10.1039/c2ce06654h

[8] S. Yu, W. Zheng, W. Yu, Y. Zhang, Q. Jiang and Z. Zhao, Formation

Mechanism of β -Phase in PVDF / CNT Composite Prepared by the Sonication

Method, Macromolecules, 42 (2009), 8870–8874.

https://doi.org/10.1021/ma901765j

[9] X. Huang, P. Jiang, C. Kim, F. Liu and Y. Yin, Influence of aspect ratio of

carbon nanotubes on crystalline phases and dielectric properties of poly

(vinylidene fluoride), Eur. Polym. J., 45 (2009), no. 2, 377–386.

https://doi.org/10.1016/j.eurpolymj.2008.11.018

[10] Y. Liu, Y. Li, J. Xu and Z. Fan, Cooperative Effect of Electrospinning and

Nanoclay on Formation of Polar Crystalline Phases in Poly (vinylidene fluoride),

ACS Applied Materials & Interfaces, 2 (2010), no. 6, 1759–1768.

https://doi.org/10.1021/am1002525

[11] K. P. Loh, Q. Bao, P. K. Ang and J. Yang, The chemistry of graphene,

Journal of Materials Chemistry, 20 (2010), 2277–2289.

https://doi.org/10.1039/b920539j

[12] S. Niyogi, E. Bekyarova, J. Hong, S. Khizroev, C. Berger, Walt de Heer, R.

C. Haddon, Covalent Chemistry for Graphene Electronics, The Journal of

Physical Chemistry Letters, 2 (2011), 2487–2498.

https://doi.org/10.1021/jz200426d

[13] K. S. Novoselov, A. K. Geim, S. V. Morozov, D. Jiang, Y. Zhang, S. V.

Dubonos, I. V. Grigorieva, A. A. Firsov, Electric Field Effect in Atomically Thin

Carbon Films, Science, 306 (2004), 666–670.

https://doi.org/10.1126/science.1102896

[14] A. K. Geim, Graphene: Status and Prospects, Science, 324 (2009), 1530-

1534. https://doi.org/10.1126/science.1158877

[15] T. Kuilla, S. Bhadra, D. Yao, N. Hoon, S. Bose and J. Hee, Recent advances

in graphene based polymer composites, Prog. Polym. Sci., 35 (2010), no. 11,

1350–1375. https://doi.org/10.1016/j.progpolymsci.2010.07.005

Characterization of the piezoelectric response of … 4807

[16] S. Schöche, N. Hong, M. Khorasaninejad, A. Ambrosio, E. Orabona, P.

Maddalena, F. Capasso, Optical properties of graphene oxide and reduced

graphene oxide determined by spectroscopic ellipsometry, Appl. Surf. Sci., 421

(2017), 778–782. https://doi.org/10.1016/j.apsusc.2017.01.035

[17] K. I. Bolotin, K.J. Sikes, Z. Jiang, M. Klima, G. Fudenberg, J. Hone, P. Kim,

H.L. Stormer, Ultrahigh electron mobility in suspended graphene, Solid State

Communications, 146 (2008), 351–355. https://doi.org/10.1016/j.ssc.2008.02.024

[18] C. González and V. Oxana, Propiedades y aplicaciones del grafeno,

Ingenierías, 11 (2008), no. 38, 17–23.

[19] A. K. Geim, K. S. Novoselov, The rise of graphene, Nature Materials, 6

(2007), 183–191. https://doi.org/10.1038/nmat1849

[20] W. Argonéz, Cite Energía, 2017.

[21] E. Choi, T. Han, J. Hong, J. Kim, S. Lee, H. Kim, S. Kim, Noncovalent

functionalization of graphene with end-functional polymers, Journal of Materials

Chemistry, 20 (2010), 1907–1912. https://doi.org/10.1039/b919074k

[22] H. Bidsorkhi, A. D’Aloia, G. De Bellis, A. Proietti, A. Rinaldi, M. Fortunato,

Paolo Ballirano, M. Bracciale, M. Santarelli, M. Sarto, Nucleation Effect of

Unmodified Graphene Nanoplatelets on PVDF / GNP Film Composites, Mater.

Today Commun., 11 (2017), 163-173.

https://doi.org/10.1016/j.mtcomm.2017.04.001

[23] M. Benz, W. B. Euler and O. J. Gregory, The Role of Solution Phase Water

on the Deposition of Thin Films of Poly (vinylidene fluoride), Macromolecules,

35 (2002), 2682–2688. https://doi.org/10.1021/ma011744f

[24] V. Eswaraiah, K. Balasubramaniam and S. Ramaprabhu, Functionalized

graphene reinforced thermoplastic nanocomposites as strain sensors in structural

health monitoring, J. Mater. Chem., 21 (2011), no. 34, 12626.

https://doi.org/10.1039/c1jm12302e

[25] I. S. Elashmawi, N. S. Aiatawia and N. H. Elsayed, Preparation and

characterization of polymer nanocomposites based on PVDF / PVC doped with

graphene nanoparticles, Results in Physics, 7 (2017), 636-640.

https://doi.org/10.1016/j.rinp.2017.01.022

[26] L. He and S. C. Tjong, A graphene oxide–polyvinylidene fluoride mixture as

a precursor for fabricating thermally reduced graphene oxide–polyvinylidene

fluoride composites, RSC Advances, 3 (2013), no. 45, 22981.

https://doi.org/10.1039/c3ra45046e

4808 Lina Marcela Hoyos Palacio et al.

[27] D. A. Dikin, S. Stankovich, E. Zimney, R. Piner, G. Dommett, G.

Evmenenko, S. Nguyen, R. Ruoff, Preparation and characterization of graphene

oxide paper, Nature, 448 (2007), no. 7152, 457–460.

https://doi.org/10.1038/nature06016

[28] S. Park and R. S. Ruoff, Chemical methods for the production of graphenes,

Nat. Nanotechnol., 4 (2009), no. 4, 217–224.

https://doi.org/10.1038/nnano.2009.58

[29] L. Huang, C. Lu, F. Wang and X. Dong, Piezoelectric property of PVDF /

graphene composite fi lms using 1H , 1H , 2H , 2H-Per fl uorooctyltriethoxysilane

as a modifying agent, J. Alloys Compd., 688 (2016), 885–892.

https://doi.org/10.1016/j.jallcom.2016.07.058

[30] S. Moharana and R. N. Mahaling, Silver (Ag)-Graphene Oxide (GO) - Poly

(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) nanostructured

composites with high dielectric constant and low dielectric loss, Chem. Phys.

Lett., 680 (2017), 31-36. https://doi.org/10.1016/j.cplett.2017.05.018

Received: October 10, 2018; Published: November 15, 2018