Dielectric Dispersion Study of Poly(vinyl Pyrrolidone)–Polar Solvent Solutions in the Frequency Range 20 Hz–1 MHz

Abstract

Influence of polar solvents environment and polymer concentrations on the electrical properties (complex dielectric constant, ac electrical conductivity, complex electric modulus and complex impedance) of the solutions of poly(vinyl pyrrolidone) (PVP) in polar solvents, namely water, ethyl alcohol, ethylene glycol, diethylene glycol, poly (ethylene glycol), glycerol, dimethyl sulfoxide and dimethyl formamide, have been investigated in the frequency range 20 Hz-1 MHz at 258C. Comparative analysis of the dielectric dispersion curves confirms that the solvent molecular size and number of its hydroxyl groups, and the solutions viscosity, are the major factors which governs the PVP chain segmental motion. The ionic conduction and electrode polarization phenomena has a dominant influence on the large increase of complex dielectric constant values of the solutions of PVP-polar solvent in the lower frequency region. The values of relaxation times corresponding to these phenomena are also reported.

Low frequency dielectric relaxation processes and ionic conductivity of montmorillonite clay nanoparticles colloidal suspension in poly(vinyl pyrrolidone)−ethylene glycol blends

“…Further, the significant increase in ε′ and ε″ values of these materials with increase of clay concentration may also be related to the formation of a percolation structure of the nanoparticles, which is confirmed by dielectric investigation on nanocomposites [37]. Pure EG, PVP-EG blends and MMT clay loaded PVP-EG blends have a large increase in the ε′ values in the lower frequency side of the spectra (Figure 1), which is mainly due to the contribution of the electrode polarization (EP) [8,[21][22][23][24] and Maxwell-Wanger (MW) interfacial polarization [38,39]. Further, the ε′ values of the MMT clay loaded PVP-EG blends monotonously increases with the increase of clay concentration, which suggests the enhancement in number of free Na + cations and their mobility in the increased spacing of intercalated clay galleries.…”

“…Figure 4 shows the 'master curves representation' [22,23,29,32,33] of the real and imaginary parts of all the intensive quantities alongwith tanδ values of 1 wt% MMT clay concentration of the solute in PVP-EG blend. It is noticed that the intersection of all the real and imaginary parts of intensive quantities occurs at the same frequency f σ , and below it direct current (dc) conduction dominates.…”

“…Figure 1 shows the frequency dependent spectra of the real part of the relative dielectric function ε′, dielectric loss ε″, and loss tangent tanδ = ε″/ε′ with varying MMT clay concentration colloidal suspension in the PVP-EG blend, at 30°C . The tanδ spectra has the peak value corresponding to the electrode polarization (EP) relaxation frequency f EP , which is used to evaluate the EP relaxation time [22][23][24][29][30][31][32][33]. The correct value of f EP of these materials were determined by tanδ(f) data fit using the Origin ® non-linear curve fitting tool.…”

“…Figure 4 shows the 'master-curves representation' of the intensive quantities of 1 wt% clay colloidal suspension in PVP-EG blend as one of the representative plot. Such plots are frequently used to find out the common intersection frequency f σ of the real and imaginary parts of all intensive quantities in the ion conduction region [22][23][24]29], which is corresponding to Maxwell-Wagner or ionic conductivity relaxation processes. In the conductivity spectra, f σ value separates the change in ions from dc to ac transport.…”

“…The BDS study of PVP-EG blends over the frequency range 20 Hz to 20 GHz are described by the sum of three relaxation processes with the contribution of dc conductivity [21]. The low frequency process (l-process) for PVP-EG blends is caused by electrode polarization and ionic conduction phenomena [21][22][23][24]. The middle frequency process (m-process) is observed corresponding to the micro-Brownian motion (local chain motion) of the PVP chain, whose time is of the order of about 10 -6 s [21,22].…”