ISSN 0965-545X, Polymer Science, Ser. A, 2011, Vol. 53, No. 5, pp. 375–384. © Pleiades Publishing, Ltd., 2011. 375 1 INTRODUCTION Polyvinylidene fluoride (PVDF) is a chemically in- ert but electronically active thermoplastic polymer. It has a variety of applications [1–8]. It is commonly used in chemical, medical and defense industries. The piezoelectric and pyroelectric responses of PVDF rival those of ceramics. Lower cost, large area, flexibility, and low acoustic impedance are among the advantages of PVDF over ceramics due to its polymeric nature. Strong piezoelectric properties, stability to UV radia- tion and high continuous-use temperature make PVDF suitable for various IR integrated optics appli- cations [5]. The cylindrical microlenses and microlens arrays can be fabricated by CO 2 laser irradiation of polyvinylidene fluoride substrate. The natural flame retardancy and flexibility of PVDF leads to many uses in the jacketing of fiber optic cables, fiber optic race- ways and copper cable used in plenum areas of build- ings. The mechanical properties and cytotoxicity (bio- compatibility) of polyvinylidene fluoride and hy- droxyapatite (HAP) composites are used in bone restoration and filling [6]. Microfabricated piezoelec- tric PVDF structures could find applications in the fabrication of mechanically active tissue engineering scaffolds, and the development of dynamic sensors at the cellular and subcellular levels. Polymer electrolytes based on polyvinylidene fluoride have wide applica- tions in lithium batteries and proton fuel cells [7]. The chemical structure of PVDF (–CH 2 –CF 2 –), intermediate between polyethylene and polytetrafluo- roethylene, gives the polymer chain both flexibility 1 The article is published in the original. and some stereo-chemical constraints. Consequently, PVDF exhibits polymorphism with at least five phases found experimentally depending on the crystallization temperature, mechanical stress, casting solvent, elec- tric field and other crystallization conditions [9]. Five crystal phases with different conformations are all- trans (ttt) planar zig-zag β-phase, tgtg' (g denotes gauche form) α- and δ-phases, and t 3 gt 3 g' γ- and ε-phases [10, 11]. Since the C–F bond is a polar bond, different phases of PVDF possess different amount of net dipole moment. The β-phase has the highest di- pole moment per unit, as in this conformation all the diploes are aligned in the same direction [12]. In the cases of polar β-, γ- and δ-phases, the polymer chains pack into crystals with parallel dipoles, hence the crys- tal possesses a net dipole moment whereas, in the cases of non-polar α- and ε-phases, they do with anti-par- allel dipoles hence the net dipole moment vanishes. Among these phases, the β-phase has the highest spontaneous polarization in a unit crystal cell [13]. The large value of unit cell polarization for an oriented and polarized sample is from the closer packing of polymer chains in a unit cell. Therefore, the polar β-phase has attracted technological interest. FTIR spectroscopy is a major technique for inves- tigating polymer sample in terms of composition as well as constituents’ distribution. Apart from different chemical distributions in the sample, the spectrosco- pist is also able to visualize areas with different degree of crystallinity or preferred orientation and by these means ensure reliable data about the quality of the in- vestigated sample, manufacturing process, etc. Raman spectroscopy is a nondestructive analytical technique and is complementary in nature to infrared spectros- Heat Capacity and Vibrational Dynamics of Polyvinylidene Fluoride (β-form) 1 Archana Gupta a , Parag Agarwal a , Saba Bee a , Poonam Tandon b , and V. D. Gupta b a Department of Applied Physics, Institute of Engineering and Technology, M. J. P. Rohilkhand University, Bareilly, India b Department of Physics, Lucknow University, Lucknow, India e-mail: drarchana.physics@gmail.com Received October 18, 2010; Revised Manuscript Received December 28, 2010 Abstract—Polyvinylidene fluoride (PVDF) is a polymer of industrial importance, mainly due to its piezo- electric and pyroelectric properties. A comprehensive study of the normal modes and their dispersion in PVDF (β-form) has been reported in the reduced zone scheme using Wilson’s GF matrix method as modified by Higgs. A Urey–Bradley force field has been used. The evaluation of normal modes and their dispersion has been taken to logical conclusion by calculating the heat capacity as a function of temperature. The extent of agreement with the experimental data supports the potential field. Characteristic features of the dispersion curves such as repulsion and exchange of character have also been discussed. DOI: 10.1134/S0965545X11050051 STRUCTURE AND PROPERTIES