Modification and processing of poly (vinylidene fluoride) (PVDF)-based Polymers towards ferroelectric thin films

• Main Author: Yee, Wu Aik.
• Other Authors: Lu, Xuehong
• Format: Theses and Dissertations
• Published: 2008
• Subjects: DRNTU::Engineering::Materials::Microelectronics and semiconductor materials::Thin films
• Online Access: http://hdl.handle.net/10356/5135
• Institution: Nanyang Technological University

In this work, thin films of poly(vinylidene fluoride) (PVDF) and poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)) were prepared via two routes, spin coating and electrospinning. It was found that electrospinning of PVDF from its N,N-dimethylformamide/acetone solutions can induce molecular orientation of PVDF chains and hence promote the formation of ?-phase. The addition of 3 wt.% of tetrabutylammonium chloride (TBAC) into the polymer solutions can effectively improve the morphology of the electrospun fibers due to the great increase in the conductivity of the solutions, and lead to almost pure ?-phase in the fibers. TBAC, a hygroscopic salt, could retain water in the fibers, which may led to hydrogen bonding between the water molecules and the fluorine atoms of PVDF and induce more trans conformers, while electrospinning induces chain orientation, which promotes inter-chain registration and hence stabilizes ?-nuclei. Modification of the rotating disk collector allowed the collection of thin films of aligned electrospun PVDF and P(VDF-TrFE) fibers, enabling the measurement of the hysteresis loops of these thin films. Electrospun PVDF performed significantly better than P(VDF-TrFE) which differs from the trend observed from spin-coated films. The degree of crystallinity and the contribution of other polar phases in electrospun PVDF fibers were believed to be the main reason for this phenomenon. The blending of PVDF and P(VDF-TrFE) across various compositions did not give rise to significant co-crystallization, regardless of the processing method used. Preliminary results of treatment of PVDF with hydrogen peroxide yielded spin-coated films with high polar phases (both ?- and ?-phase) with impressive a-phase suppression, allowing a one step method to produce films with high polar phase content.