Effect of multi-step processing on the structural, morphological and dielectric behaviour of PVDF films
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ORIGINAL PAPER
Effect of multi-step processing on the structural, morphological and dielectric behaviour of PVDF films Suvrajyoti Mishra 1 & Rajesh Sahoo 1 & Lakshmi Unnikrishnan 1 & Ananthakumar Ramadoss 1 & Smita Mohanty 1 & Sanjay Kumar Nayak 1 Received: 27 June 2020 / Revised: 12 August 2020 / Accepted: 1 September 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract In this work, we have reported the systematic preparation of flexible and transparent PVDF films, through multi-step processing techniques including solvent casting followed by thermal compression and mechanical stretching. Variation in the structural, morphological and dielectric behaviour of each film with respect to each processing condition are analysed through FTIR, XRD, DSC, FESEM, AFM and impedance spectroscopy. The structural characterisation revealed the deep influence of thermal compression and mechanical stretching process on the electroactive ß-phase structure of solvent-casted PVDF films while the morphological analysis confirmed the formation of microfibrillar morphology after three successive processing methods. A significant increment in the dielectric constant value from 10.7 (for solvent-casted PVDF film) to 24 (for solvent-casted followed by thermal compression followed by mechanical stretched PVDF film) and dielectric loss of 0.015 to 0.0018 has achieved for PVDF film after multi-step processing techniques. Such improvements in structural and dielectric behaviour are attributed to the thermo and mechanical dependent changes in the crystalline structure which helps in the rotation of polar –CH2-CF2 group. Keywords PVDF . Electroactive . Structural . Dielectric . Processing
Introduction Polyvinylidene fluoride, PVDF, is a multifaceted semicrystalline polymeric material with unique piezoelectric and ferroelectric properties. Additionally, it has better mechanical strength, fracture tolerance, flexibility, light weight, chemical resistance and easy processing methods as compared with piezoelectric ceramic materials. The presence of three most common crystalline phases, such as α, ß and γ, helps in distinguishing between the existence of electroactive polar phases and non-polar phases in PVDF. These phases are different from each other in terms of conformation, arrangement of molecules and crystallographic space groups. Non-polar αphase possess TGTG′ (trans-gauche–trans-gauche) conformation with anti-parallel arrangement of dipoles and the γ-phase * Suvrajyoti Mishra [email protected] 1
School for Advanced Research in Polymers (SARP)-LARPM, Central Institute of Plastics Engineering & Technology (CIPET), B/ 25, CNI Complex, (PO) KIIT, Patia, Bhubaneswar, Odisha 751024, India
possess TTTG′ (trans-trans–trans-gauche) arrangement of dipoles, whereas polar ß-phase has all trans (TTT) chain conformation. Among all phases of PVDF, α-phase is the most stable phase and very easily obtained directly from the melt. ßPhase is the most important crystalline electroactive phase due to their greater dipole moment (8
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