**11. Polarization switching properties of PVDF homopolymer films**

PVDF homopolymer thin films have been prepared by the Langmuir–Blodgett technique, and their electrical properties have comprehensively been studied [36]. The PVDF homopolymer films show better ferroelectricity with higher polarization and higher breakdown electric field than that of P(VDF-TrFE) copolymer films.

**Figure 18.** *P-E* loops of PVDF and P(VDF-TrFE) copolymer LB films

The phase image of the piezoresponse shows a polarization switching in the PVDF homopol‐ ymer films, suggesting a typical ferroelectric feature. The ferroelectric *P-E* loops of the PVDF homopolymer and P(VDF-TrFE) films are shown in Fig. 18. The well *P-E* hysteresis loop of the PVDF films also confirms its ferroelectricity. It can also be seen that both the *Pr* and *Ec* of the PVDF LB films are higher than that of P(VDF-TrFE) LB films. In addition, the breakdown voltage of the PVDF LB films is found to be above 50 V, whereas the breakdown voltage of the P(VDF-TrFE) LB films is only 40 V. both the *Pr* and *Ec* of the PVDF LB films are higher than that of P(VDF-TrFE) LB films. In addition, the breakdown voltage of the PVDF LB films is found to be above 50 V, whereas

the breakdown voltage of the P(VDF-TrFE) LB films is only 40 V.

homopolymer films, suggesting a typical ferroelectric feature. The ferroelectric *P-E* loops of

hysteresis loop of the PVDF films also confirms its ferroelectricity. It can also be seen that

Figure 19 (a) The P-E loops of the PVDF homopolymer LB films with 10 to 200 transferred layers. (b) Log *Ec* vs.log thickness of the PVDF homopolymer LB films **Figure 19.** (a) The P-E loops of the PVDF homopolymer LB films with 10 to 200 transferred layers. (b) Log *Ec* vs.log thickness of the PVDF homopolymer LB films

In this study, the film thickness dependence of the *Ec* of the PVDF homopolymer LB films is investigated. Figure 19(a) shows the *P-E* loops of the PVDF homopolymer LB films with various transferred layers. Note that the *Ec* is basically constant between 200 nm and 44 nm but dramatically increases with the thickness decreasing in the range from 45 nm to 11 nm (Fig. 19(b)). Thus, the switching in the thicker thickness range is attributed to be extrinsic. Further investigation on the thickness dependence of the *Ec* of our PVDF homopolymer films in the thinner thickness range, i.e., from 45 nm to 11 nm, reveals that the relationship In this study, the film thickness dependence of th*e Ec* of the PVDF homopolymer LB films is investigated. Figure 19(a) shows the *P-E* loops of the PVDF homopolymer LB films with various transferred layers. Note that the *Ec* is basically constant between 200 nm and 44 nm but dramatically increases with the thickness decreasing in the range from 45 nm to 11 nm (Fig. 19(b)). Thus, the switching in the thicker thickness range is attributed to be extrinsic. Further investigation on the thickness dependence of the *Ec* of our PVDF homopolymer films in the thinner thickness range, i.e., from 45 nm to 11 nm, reveals that the relationship basically complies with the semi-empirical scaling law of the Janovec–Kay–Dunn (JKD) scaling, suggesting that the switching is neither extrinsic nor intrinsic in this range.

basically complies with the semi-empirical scaling law of the Janovec–Kay–Dunn (JKD)

PVDF-based ferroelectric polymers have been studied for many years, and

scaling, suggesting that the switching is neither extrinsic nor intrinsic in this range.

#### **Conclusion 12. Conclusion**

these polymers have been widely used in many electronic devices, for example, transducers, actuators, switches, and infrared sensors. Nonetheless, there are lots of novel properties that need to be explored. In this chapter, the LB method has been used for preparing ultrathin films of PVDF-based films. In addition, many special characteristics of these films have been generalized. These special PVDF-based ferroelectric polymers have been studied for many years, and widely used in many electronic devices, for example, transducers, actuators, switches, and infrared sensors. Nonetheless, there are lots of novel properties that need to be explored. In this chapter, the LB method has been used for preparing ultrathin films of PVDF-based films. In addition, many special characteristics of these films have been generalized. These special properties include high tunability, huge electrocaloric effect, polarization switching, self-polarization, and enhanced electric properties in the artificial polymer multilayers. Besides these properties and potential applications, ferroelectric polymers possess many other advantag‐ es for applications. The advantages of this type of ferroelectric polymers include low cost, ease and flexibility of fabrication in different kinds of thin film forms, and resistance to degradation caused by strain. PVDF-based polymers are also more readily altered to conform to complex device requirements imposed by the environment, size, shape, physical

flexibility, reliability, durability, and other constraints. PVDF-based films can be easily patterned for integrated electronic applications.
