Dielectric relaxation strength and magnitude of dipole moment of poly (vinyl pyrrolidone)in polar solutions Naoki Shinyashiki ⁎, Masahiko Miyara, Shinya Nakano, Wataru Yamamoto, Masahiro Ueshima, Daizo Imoto, Kaito Sasaki, Rio Kita, Shin Yagihara Department of Physics, Tokai University, Hiratsuka, Kanagawa 259-1292, Japan abstract article info Article history: Received 9 August 2012 Received in revised form 16 February 2013 Accepted 27 February 2013 Available online 15 March 2013 Keywords: Dielectric relaxation strength Dielectric constant Dipole moment Polymer solution Polar solvent Poly(vinyl pyrrolidone) Dielectric relaxation caused by the segmental motion of poly(vinyl pyrrolidone) (PVP) was observed in solutions at 25 °C with various solvents, that is, chloroform, water, and mono- and dihydroxyl alcohols with dielectric con- stants ranging between 5 and 78. The relaxation strength of the segmental motion of PVP varies with the solvent. The magnitudes of the effective dipole moment of the repeat unit of PVP in solutions with various solvents cal- culated using the Onsager equation depends simply on the dielectric constant of the solvent at higher frequency. © 2013 Elsevier B.V. All rights reserved. 1. Introduction There is much literature on the theory and practice of the depen- dence of dielectric relaxation strength, Δε, on the magnitude and density of the dipole moment, the Kirkwood g-factor, internal elec- tric field, and temperature for various systems including polymers [1–7]. The mobility of chains is considered to be limited owing to the entanglement of chains in bulk polymer systems, and the rela- tionship between dielectric relaxation strength and the magnitude of the dipole moment on the polymer has been studied mainly for the relaxation of a polymer in solution. The dielectric relaxation due to the local segmental motion of the polymer had been studied for polymer solutions with nonpolar solvents. The dielectric con- stants of nonpolar solvents are approximately in the range between 2 and 3. In general, the Kirkwood g-factor has been introduced to in- terpret the difference between the magnitude of the dipole moment in solution obtained using the Onsager equation [8] and that obtained in gas. In this case, the g-factor has been discussed on the basis of the idea that the estimation of the internal electric field is correct, since this small range of the dielectric constant of the solvent is insufficient to distinguish the effect of the internal electric field from that of the Kirkwood g-factor. Poly(vinyl pyrrolidone) (PVP) is a semicrystalline synthetic poly- mer that forms a randomly coiled and highly flexible chain in polar solvents. Moreover, PVP is soluble in various kinds of liquids. The di- electric behavior of PVP solutions in water [9–22], alcohol [20,23], ethylene glycol oligomer (EGO) [24,25], and chloroform [26] has been studied extensively in the frequency range of 20 Hz–20 GHz at 25 °C. Two processes of relaxation due to the reorientation of di- poles on PVP and the solvent were observed. The relaxation process at frequencies higher than 100 MHz is the primary process of sol- vents, and that at frequencies lower than 10 MHz is attributed to the local segmental chain motion of PVP. Different time scales of the molecular motion of the polymer and solvent coexist in homoge- neous mixtures. For these PVP solutions, the dielectric constant of solvents is in the range between approximately 5 and 78. Therefore, we used PVP solutions since they are perfect systems for the investi- gation of the relationships among the dielectric relaxation strength of the segmental motion of a polymer, the magnitude of the dipole moment of the repeat unit of polymer, and the dielectric constant of the solvent. No one has ever observed the effect of the type of sol- vent on the relaxation strength of a polymer in solvent with such a wide range of dielectric constant. The details of the structure and di- pole moment of a repeat unit of PVP are shown in Fig. 1 in Ref. [26]. The repeat unit of PVP has a permanent dipole moment with a mag- nitude of 3.53 Debye [26] (1 Debye = 3.33564 × 10 -30 C·m). The magnitude of the dipole moment on a repeat unit of PVP can be treat- ed as constant, since the side group of PVP has no internal freedom [26], and PVP possesses only the acceptor of the hydrogen bond, Journal of Molecular Liquids 181 (2013) 110–114 ⁎ Corresponding author. Tel.: +81 463 58 1211; fax: +81 463 50 2013. E-mail address: naoki-ko@keyaki.cc.u-tokai.ac.jp (N. Shinyashiki). 0167-7322/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.molliq.2013.02.020 Contents lists available at SciVerse ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq