Real time dielectric monitoring of glass transition in n-vinyl pyrrolidone polymerization

Real time dielectric spectroscopy was used for monitoring the dynamics during liquid glass transition in radical bulk polymerization of n-vinyl pyrrolidone. Two different relaxation mechanisms were identified. Initially segmental α-relaxation was dominant. Subsequently, contribution from slower motions became more significant and ε′(tr, ω) underwent maxima in all frequency bands up to 10 MHz. Peak amplitude increased and the occurring time was delayed with decreasing frequency. The slow region dynamics were similar to the dynamics of Chamberlin's domain-like model of glass transition. The glassy phase is formed by a segmental relaxation and a relaxation due to glassy regions. The characteristic relaxation times of slow and segmental motions were well described by a modified Vogel-Fulcher-Tammann relation. The high frequency behavior, associated with the segmental motions, is well described by Havriliak-Negami and Kohlrausch-Williams-Watts formulas, which did not provide satisfactory fittings for the dynamics of slow regions. Both real and imaginary parts of the dielectric data were fully described by a complex dielectric relaxation function, the parameters of which are found by the eigen-coordinates (EC) method. © 2007 Elsevier B.V. All rights reserved

Experimental confirmation of oscillating properties of the complex conductivity: Dielectric study of polymerization/vitrification reaction

Clear evidence of the existence of fractional kinetics containing the complex power-law exponents were obtained by conductivity measurements of polymerization reaction of polyvinylpyrrolidone (PVP) performed inside a dielectric cell. We established the relationship between the Fourier image R(jω) of the complex memory function K(t) and the time-dependent mean square displacement 〈r2(t)〉. This relationship helps to understand the origin of the different power-law exponents appearing in the real part of complex conductivity Re[σ(ω)] and find a physical/geometrical meaning of the power-law exponents that can form the complex-conjugated values. The complex-conjugated values of the power-law exponents leading to oscillating behavior of conductivity follows from the fractional kinetics suggested by one of the authors (R.R.N.). The relationships [R(jω)⇔Re[σ(ω)]⇔〈r2(t)〉] are becoming very efficient in classification of different types of collective motions belonging to light and heavy carriers involved in the relaxation/transfer process. The conductivity data obtained for Re[σ(ω)] during the whole polymerization process of the PVP at different temperatures (80, 90, 100 °C) are very well described by the fitting function that follows from the suggested theory. Original fitting procedure based on the application of the eigen-coordinates (ECs) method helps to provide a reliable fitting procedure in two stages and use the well-developed and statistically stable linear least square method (LLSM) for obtaining the correct values of the fitting parameters that describe the behavior of Re[σ(ω, Tr)] in the available frequency range for the current time of the chemical reaction Tr measured during the whole process of polymerization. The suggested theory gives a unique possibility to classify the basic types of motions that take place during the whole polymerization process. © 2007

The first experimental confirmation of the fractional kinetics containing the complex-power-law exponents: Dielectric measurements of polymerization reactions

For the first time we achieved incontestable evidence that the real process of dielectric relaxation during the polymerization reaction of polyvinylpyrrolidone (PVP) is described in terms of the fractional kinetic equations containing complex-power-law exponents. The possibility of the existence of the fractional kinetics containing non-integer complex-power-law exponents follows from the general theory of dielectric relaxation that has been suggested recently by one of the authors (R.R.N). Based on the physical/geometrical meaning of the fractional integral with complex exponents there is a possibility to develop a general theory of dielectric relaxation based on the self-similar (fractal) character of the reduced (averaged) microprocesses that take place in the mesoscale region. This theory contains some essential predictions related to existence of the non-integer power-law kinetics and the results of this paper can be considered as the first confirmation of existence of the kinetic phenomena that are described by fractional derivatives with complex-power-law exponents. We want to stress here that with the help of a new complex fitting function for the complex permittivity it becomes possible to describe the whole process for real and imaginary parts simultaneously throughout the admissible frequency range (30 Hz-13 MHz). The fitting parameters obtained for the complex permittivity function for three temperatures (70, 90 and 110 °C) confirm in general the picture of reaction that was known qualitatively before. They also reveal some new features, which improve the interpretation of the whole polymerization process. We hope that these first results obtained in the paper will serve as a good stimulus for other researches to find the traces of the existence of new fractional kinetics in other relaxation processes unrelated to the dielectric relaxation. These results should lead to the reconsideration and generalization of irreversibility and kinetic phenomena that can take place for many linear non-equilibrium systems. © 2006 Elsevier B.V. All rights reserved

Pyroelectric effect and polarization instability in self-assembled diphenylalanine microtubes

The natural ability of peptides and proteins to self-assemble into elongated fibrils is associated with several neurogenerative diseases. Diphenylalanine (FF) tubular structures that have the same structural motif as in Ab-amyloid peptide (involved in Alzheimer's disease) are shown to possess remarkable physical properties ranging from piezoelectricity to electrochemical activities. In this work, we also discover a significant pyroelectric activity and measure the temperature dependence of the pyroelectric coefficient in the temperature range of 20-100 degrees C. Pyroelectric activity decreases with temperature contrary to most ferroelectric materials and significant relaxation of pyrocurrent is observed on cooling after heating above 50 degrees C. This unusual behavior is assigned to the temperature-induced disorder of water molecules inside the nanochannels. Pyroelectric coefficient and current and voltage figures of merit are estimated and future applications of pyroelectric peptide nanostructures in biomedical applications are outlined. Published by AIP Publishing

Novel supramolecular biomaterials for piezoelectric applications

The equipment of Ural Center for Shared Use "Modern Nanotechnology" UrFU has een used. This work was supported by the FCT project TUBITAK/0006/2014 (Portugal)

Real time dielectric monitoring of glass transition in n-vinyl pyrrolidone polymerization

Real time dielectric spectroscopy was used for monitoring the dynamics during liquid glass transition in radical bulk polymerization of n-vinyl pyrrolidone. Two different relaxation mechanisms were identified. Initially segmental α-relaxation was dominant. Subsequently, contribution from slower motions became more significant and ε′(tr, ω) underwent maxima in all frequency bands up to 10 MHz. Peak amplitude increased and the occurring time was delayed with decreasing frequency. The slow region dynamics were similar to the dynamics of Chamberlin's domain-like model of glass transition. The glassy phase is formed by a segmental relaxation and a relaxation due to glassy regions. The characteristic relaxation times of slow and segmental motions were well described by a modified Vogel-Fulcher-Tammann relation. The high frequency behavior, associated with the segmental motions, is well described by Havriliak-Negami and Kohlrausch-Williams-Watts formulas, which did not provide satisfactory fittings for the dynamics of slow regions. Both real and imaginary parts of the dielectric data were fully described by a complex dielectric relaxation function, the parameters of which are found by the eigen-coordinates (EC) method. © 2007 Elsevier B.V. All rights reserved

Real time dielectric monitoring of glass transition in n-vinyl pyrrolidone polymerization

Real time dielectric spectroscopy was used for monitoring the dynamics during liquid glass transition in radical bulk polymerization of n-vinyl pyrrolidone. Two different relaxation mechanisms were identified. Initially segmental α-relaxation was dominant. Subsequently, contribution from slower motions became more significant and ε′(tr, ω) underwent maxima in all frequency bands up to 10 MHz. Peak amplitude increased and the occurring time was delayed with decreasing frequency. The slow region dynamics were similar to the dynamics of Chamberlin's domain-like model of glass transition. The glassy phase is formed by a segmental relaxation and a relaxation due to glassy regions. The characteristic relaxation times of slow and segmental motions were well described by a modified Vogel-Fulcher-Tammann relation. The high frequency behavior, associated with the segmental motions, is well described by Havriliak-Negami and Kohlrausch-Williams-Watts formulas, which did not provide satisfactory fittings for the dynamics of slow regions. Both real and imaginary parts of the dielectric data were fully described by a complex dielectric relaxation function, the parameters of which are found by the eigen-coordinates (EC) method. © 2007 Elsevier B.V. All rights reserved

Real time dielectric monitoring of glass transition in n-vinyl pyrrolidone polymerization

Real time dielectric spectroscopy was used for monitoring the dynamics during liquid glass transition in radical bulk polymerization of n-vinyl pyrrolidone. Two different relaxation mechanisms were identified. Initially segmental α-relaxation was dominant. Subsequently, contribution from slower motions became more significant and ε′(tr, ω) underwent maxima in all frequency bands up to 10 MHz. Peak amplitude increased and the occurring time was delayed with decreasing frequency. The slow region dynamics were similar to the dynamics of Chamberlin's domain-like model of glass transition. The glassy phase is formed by a segmental relaxation and a relaxation due to glassy regions. The characteristic relaxation times of slow and segmental motions were well described by a modified Vogel-Fulcher-Tammann relation. The high frequency behavior, associated with the segmental motions, is well described by Havriliak-Negami and Kohlrausch-Williams-Watts formulas, which did not provide satisfactory fittings for the dynamics of slow regions. Both real and imaginary parts of the dielectric data were fully described by a complex dielectric relaxation function, the parameters of which are found by the eigen-coordinates (EC) method. © 2007 Elsevier B.V. All rights reserved

Experimental confirmation of oscillating properties of the complex conductivity: Dielectric study of polymerization/vitrification reaction

Clear evidence of the existence of fractional kinetics containing the complex power-law exponents were obtained by conductivity measurements of polymerization reaction of polyvinylpyrrolidone (PVP) performed inside a dielectric cell. We established the relationship between the Fourier image R(jω) of the complex memory function K(t) and the time-dependent mean square displacement 〈r2(t)〉. This relationship helps to understand the origin of the different power-law exponents appearing in the real part of complex conductivity Re[σ(ω)] and find a physical/geometrical meaning of the power-law exponents that can form the complex-conjugated values. The complex-conjugated values of the power-law exponents leading to oscillating behavior of conductivity follows from the fractional kinetics suggested by one of the authors (R.R.N.). The relationships [R(jω)⇔Re[σ(ω)]⇔〈r2(t)〉] are becoming very efficient in classification of different types of collective motions belonging to light and heavy carriers involved in the relaxation/transfer process. The conductivity data obtained for Re[σ(ω)] during the whole polymerization process of the PVP at different temperatures (80, 90, 100 °C) are very well described by the fitting function that follows from the suggested theory. Original fitting procedure based on the application of the eigen-coordinates (ECs) method helps to provide a reliable fitting procedure in two stages and use the well-developed and statistically stable linear least square method (LLSM) for obtaining the correct values of the fitting parameters that describe the behavior of Re[σ(ω, Tr)] in the available frequency range for the current time of the chemical reaction Tr measured during the whole process of polymerization. The suggested theory gives a unique possibility to classify the basic types of motions that take place during the whole polymerization process. © 2007

Dielectric study of neutral and charged hydrogels during the swelling process

Dielectric spectroscopy measurements of conductivity were applied for understanding the change in the internal morphology of the neutral and permanently charged polyacrylamide (PAAm) hydrogels during the swelling process. For the first time four distinct peaks (each corresponding to a different swelling stage) in the conductivity of the neutral gel were observed during the swelling of this gel. These peaks are related to the distribution of dense polymer regions (they are defined as the "blobs") appearing in a microstructure of the given PAAm gel having at least four average sizes. For the charged gel the heterogeneity decreases due to the internal electric field of the charged sites. Thus, this characteristic behavior in the conductivity becomes almost negligible for the gel charged with permanent S O3- groups. It seems this fact causes considerable decrease in amplitude of the peaks and overall decrease the conductivity during the whole swelling process especially at high frequencies. The new theory of dielectric relaxation based on the fractional kinetics containing the complex power-law exponents was used for verifying these swelling processes and received an excellent confirmation in description of the real part of the complex conductivity Re [ (ω)] by the fitting function that follows from the suggested theory. The calculated power-law exponents describe the behavior of Re [ (ω,m m0)] in the available frequency range (30 Hz-13 MHz) and for all values of the relative masses (volumes) measured in the process of the experiment. The excellent coincidence between the new theory and measured data gives a possibility to suggest more reliable physical picture of the swelling process that takes place in neutral/charged gels. © 2006 American Institute of Physics