**4. Conclusions**

In conclusion, electrospinning fibers and thermal compression of the fiber mats enhanced the availability of the interfacial charges, dielectric constant, electroactive β-phase, and electrostrictive coefficient content in P(VDF-HFP). The high electrostatic field in the electrospinning process caused orientation polarization, which apparently helped transform non-polar α-phase to electroactive β-phase in the formed fibers. Increasing the voltage during electrospinning increased the β-phase fraction in fibers from 74.11% to 85.90%. In this study, compressing P(VDF-HFP) fiber mats at 80 ◦C gave the highest, 89.65%, β-phase fraction among the cases tested. In addition, the dielectric constant and the crystallinity increased with the compression temperature up to 80 ◦C. This case gave the maximal observed dielectric constant of 8.4 at 1 Hz and also had the largest absolute β fraction (%β) of about 49.33% among the cases tested. Thus, the electrospinning and thermal compressing coupling processes can enhance the induced interfacial polarization, and β-phase leads to the high electrostrictive properties of obtained P(VDF-HFP) nanofibers.

**Author Contributions:** N.T. prepared and fabricated all samples. N.T. and C.P. planned and performed the experiments, characterization and data analysis. N.T., C.P., and N.M. wrote the text and reviewed the manuscript. N.M. and C.P. supported equipment and supervision.

**Funding:** This research was supported by the Science Achievement Scholarship of Thailand and research funding from graduate school, Prince of Songkla University, Thailand.

**Acknowledgments:** The authors are profoundly grateful to the Department of Physics and the Center of Excellence in Nanotechnology for Energy at the Prince of Songkla University for equipment and other support.

**Conflicts of Interest:** The authors declare no conflict of interest.
