An approach to durable poly(vinylidene fluoride) thin film loudspeaker
- PDF / 355,179 Bytes
- 8 Pages / 612 x 792 pts (letter) Page_size
- 63 Downloads / 168 Views
J.Y. Kim, D.E. Lee, and J. Joo Department of Physics and Center for Electro and Photo Responsive Molecules, Korea University, Seoul 136-701, Korea
S. Han, Y.W. Beag, and S.K. Koh P&I Corporation, Seoul 131-221, Korea (Received 28 February 2003; accepted 29 September 2003)
The piezoelectric poly(vinylidene fluoride) (PVDF) surface possessing low surface energy was modified by the ion-assisted-reaction (IAR) method for the application of thin film speaker. The IAR-treated hydrophilic PVDF surface was investigated using atomic force microscopy and x-ray photoelectron spectroscopy. The adhesion strength between various types of electrodes and the film was dramatically improved due to the hydrophilic functional groups, such as –C–O–, –(C⳱O)–, –(C⳱O)–O–, and so forth. A durable loudspeaker film was fabricated by enhancing the adhesion between the screen-printed poly(3,4-ethylenedioxythiophene)/poly(4-styrenesulfonate) (PEDOT/PSS) and the modified PVDF films. The PVDF speaker film with the PEDOT/PSS electrode showed higher durability, flatter sound pressure level characteristics, and easier processability compared to metals or indium tin oxide electrodes.
I. INTRODUCTION
Since the discovery of the piezoelectric property of poled poly(vinylidene fluoride) [PVDF; (CH2–CF2)n] in 1969,1 the physical and chemical properties of PVDF have been studied in various applications2–4 due to its low density, mechanical flexibility, thermal stability, and high-dielectric constant.5,6 PVDF is a semicrystalline polymer with about 50% crystallinity, and the dipole moment of CF2 segments in the chain align normal to the surface of the polymer film after a stretching and a poling process. The piezoelectric and pyroelectric properties of the film have widely been investigated, but not in optical applications due to the small second-order nonlinear optical effect.7,8 Various derivatives and copolymers of PVDF materials, such as P(VDF/TrFE) (trifluoroethylene),9 P(VDF/ TFE) (tetrafluoroethylene),10 and PVDF-conducting polymers,11,12 have been studied because the crystallinity and morphology of PVDF contributes to its ferroelectric property. In the case of P(VDF/TrFE), the copolymer crystallizes directly into a polar  phase. Irradiation of a)
Address all correspondence to this author. e-mail: [email protected]
2904
http://journals.cambridge.org
J. Mater. Res., Vol. 18, No. 12, Dec 2003 Downloaded: 11 Mar 2015
the P(VDF/TrFE) copolymer with high-energy electron beams reduces the coercive field and narrows the hysteresis loop.13 Composites of ceramics and the polymers were also studied to improve the piezoelectric and pyroelectric response.14,15 Active control of sound radiations from PVDF volume displacement sensor has been reported,16 and acoustic transducers, such as microphones, tweeters, and headphones, using piezoelectric constant were produced in 1975.17 Lotton et al.18 proposed a model to describe the dynamic behavior of laterally radiating piezoelectric loudspeakers. However, considering processability and simplicity of the
Data Loading...
