H.A. Kołodziej

Dielectric properties of single crystals of the substituted diacetylene pTS: effect of the solid-state polymerization and phase transitions

Abstract Dielectric permittivities of the polymerizable organic solid, p TS diacetylene have been measured between 115 and 330 K in the directions parallel and perpendicular to the direction of polymer chain growth. The upper phase transition in monomer, polymer and mixed crystals at various stages of the solid-state polymerization manifests itself as a maximum in the temperature dependence of e measured in the direction parallel to the molecular stacks, being particularly well pronounced in fully polymerized crystals. The transition was identified as an antiferroelectric one, the sublattice polarization being most probably the order parameter. The lower phase transition could be observed only in monomer and monomer-rich crystals as a shoulder on the e( T ) dependence. This transition could be detected only in the crystals containing less than ≈ 10–15% of polymer. The dielectric permittivity was found to be independent of frequency up to 3 GHz. The polymerization results in changes of the dielectric permittivity. In samples where the direction of measurements coincides with the b axis, these changes follow the monomer-polymer conversion curve.

1H-NMR, dielectric and calorimetric studies of molecular motions in m-nitroaniline crystal

Abstract Spin-lattice relaxation time, T 1 , spin-lattice relaxation time in the rotating frame, T 1 ρ , and the second moment of the resonance line measurements at 80 MHz and over the 190–380 K temperature range are reported for protons in the optically nonlinear material m -nitroaniline ( m -NA). T 1 has also been measured for samples irradiated by low energy and low intensity radiation. The real and imaginary parts of electric permittivity as well as tan  δ have been recorded in the 80–380 K temperature range at frequencies ranging from 100 Hz to 1.0 MHz. DSC measurements have been performed in the 110–387 K temperature range. Two phase transitions have been found: A glassy to rotative transition at 160 K and a plastic to plastic transformation at 365 K. The main feature of the m -NA crystal is that its plasticity continues to grow as the temperature increases. The reorientations of phenyl rings, the –NH 2 group proton 180° jumps, the lattice distortions caused by anisotropic thermal expansion and the cooperative reorientations of big molecular aggregates are thought to be the reasons for phase transitions and for the subsequent intermolecular charge transfer. The results are discussed with respect to optical second harmonic generation and near-IR photochemical reaction found in the m -NA crystal.

Thermally induced rearrangement of hydrogen-bonded helices in solid 4-isopropylphenol as studied by calorimetric, proton NMR, dielectric and near IR spectroscopic methods

Abstract Calorimetric, dielectric and Fourier transform near infrared (IR) spectroscopic methods were used to study molecular dynamics and structural transition in solid 4-isopropylphenol (4IP) above room temperature. Pulse proton nuclear magnetic resonance (NMR) measurements were performed in the 100–340 K temperature range. A phase transition was found at 331.5 K, 1.5 K below the melting point. Energetically inequivalent methyl groups reorientations were observed in differently prepared samples and this suggested that a high-temperature polymorph occurs below the transition point as a metastable phase. Dielectric relaxation measurements showed an electric conductivity similar in value to that in water. This was detected as a pronounced contribution to the imaginary part of dielectric permittivity at temperatures higher than 310 K. Near IR spectra revealed that hydrogen bondings are stronger in the high-temperature phase than in the room-temperature-stable one. We propose that thermally induced molecular rearrangements enable proton transfer in hydrogen bonds (HBs) and this stimulates protonic conduction.

Experimental and theoretical approach to the molecular dynamics of pyridine and related molecules. V. Dielectric relaxation and conformational calculations on 1,2-di-(2-pyridyl)- and 1-(3-pyridyl)-2-(4-pyridyl)-ethylenes and 4-styrylpyridine

Abstract Dielectric absorption measurements have been carried out on two trans-1,2-di-(2-pyridyl)- (2,2′-DPE) and 1-(3-pyridyl)-2-(4-pyridyl)-ethylenes (3,4′-DPE) and on trans-styrylpyridine in mesitylene in the temperature range 293–323 K, and from a static frequency up to 10 GHz. The results are interpreted in terms of relaxation both via overall molecular motion and by internal rotation. The model of “chemical relaxation” (Goulon—Rivail) is shown to be very useful and kinetic parameters are obtained. Semi-empirical calculations have also been performed for 2,3′-DPE.

Experimental and theoretical approach to the molecular dynamics of pyridine and related molecules. IV. Dielectric relaxation of trans 1-(2-pyridyl)-2-(4-pyridyl)-, 1-(2-pyridyl)-2-(3-pyridyl)-, and 1,2-di-(3-pyridyl)-ethylenes in a non-polar solvent

Abstract Dielectric relaxation measurements were carried out on three trans isomers 1-(2-pyridyl)-2-(4-pyridyl)-ethylene (2.4′-DPE), 1-(2-pyridyl)-2-(3-pyridyl)-ethylene (2.3′-DPE) and 1.2-di-(3-pyridyl)-ethylene (3.3′-DPE) in mesitylene in the temperature range 293–323 K, and from static frequency up to 10.56 GHz. Two dielectric absorption regions were found for 2.4′- and 2.3′-DPE but only one for the third isomer 3.3′-DPE. Dielectric relaxation times as well as thermodynamic activation parameters for the dielectric process were determined and are discussed comparatively. It is deduced that internal rotation very probably takes place around the bonds between the pyridine rings and the ethylene moiety. As regards the model, results were interpreted according to the Goulon-Rivail theory.

Dielectric relaxation in methylammonium chromium sulphate dodecahydrate

The complex electric permittivity of methylammonium chromium sulphate dodecahydrate over the frequency range 80–1000 MHz has been measured at temperatures near the transition point. Single relaxation time was established and the validity of the “critical retardation” model was confirmed.

The reorientational motion of substituted benzenes in the crystalline state. Dielectric relaxation of orthodinitrotetramethylbenzene and orthodinitrotetrachlorobenzene

Abstract Dielectric relaxation measurements have been performed on monocrystals of orthodinitrotetramethylbenzene and orthodinitrotetrachlorobenzene in the frequency and temperature ranges 1 kHz-1000 MHz and 280–450 K, respectively. In addition, scanning calorimetric as well as X-ray measurements have been carried out. From the results obtained a possible mechanism has been suggested as regards the dielectric relaxation process.

Dielectric, acoustic, densimetric and viscosimetric investigations of the tributylamine + propionic acid system

Data obtained at 293 K and atmospheric pressure by different experimental techniques, dielectric, acoustic, densimetric and viscosimetric, give an almost uniform picture of the structure of the investigated binary mixture. The extrema observed at the concentration range 70–75 mol% of propionic acid are explained as a result of the formation of amine–acid associates of composition 1:n where n≈3. Analysis of the dielectric relaxation parameters suggests a high flexibility of these associates.

An algorithm to be used in the lumped-capacitance method for measurements of complex dielectric permittivity in systems with large tanδ from 100 MHz to 18 GHz

An algorithm for the lumped-capacitance method is described which enables computation of permittivity and losses of ferroelectric crystals to be made. The graphical method for the solution of the algorithm by means of specially prepared diagrams is proposed. The method gives the possibility of finding from the measurement data a proper solution independently of the geometrical dimension of the sample.

The reorientational motion of substituted benzenes in the crystalline state: phase transition and dielectric relaxation of nitropentachlorobenzene and tetrachlorometaxylene

Abstract Dielectric relaxation measurements have been performed on nitropentachlorobenzene and tetrachlorometaxylene in the frequency range 100 Hz to 1 MHz and in the temperature range 152–400 K. In addition, scanning calorimetric measurements have been carried out. From the results obtained, a possible mechanism has been suggested as regards the dielectric relaxation process.