Cooperative relaxation modes associated with transitions of various systems have been experimentally resolved into elementary processes characterized by activation enthalpies and entropies following a compensation law. Two transitions with no kinetic effect-solid-solid transition and Curie transition have been studied. In both cases, the corresponding dielectric relaxations are characterized by a compensation phenomenon with transition temperature as the compensation temperature. Dielectric relaxations liberated at the glass transition, T g , have also been studied. They are also associated with a compensation law but, in that case, the compensation temperatures T g + 10/30°. This lag has been attributed to the kinetic character of T g . Note that it is lower in amorphous polymers than in semicrystalline polymers. The distribution function of activation parameters is broader in amorphous polymers than in semicrystalline ones.

Study of cooperative relaxation modes in complex systems by thermally stimulated current spectroscopy

On the electronic transport mechanism in thin films of some new poly(azomethine sulfone)s

Adsorption-induced unusual changes in the electrical conductivity of ferrocene

The influence of the plasticiser DOP on electric conduction and dielectric relaxation in polyvinyl chloride has been investigated. The results were explained in terms of the compensation law between the pre-exponential factor of an Arrhenius equation and its activation energy. This compensation law has been observed not only in electric conductivity and dielectric relaxation but also in mobility and carrier density. The basis for the compensation law has also been discussed theoretically from a thermal expansion point of view.

The compensation law in electric conduction and dielectric relaxation for polyvinyl chloride

The low temperature dielectric relaxation of porcine aortic valves and its main macromolecular proteins. i.e. elastin and collagen, have been investigated in the dry state and at low levels of hydration by thermally stimulated currents spectrometry, with an equivalent frequency of 10(-3) Hz. Two secondary relaxation modes, labeled gamma and beta with increasing temperature, are found for the three materials. Since the gamma-mode is independent upon hydration while the beta-mode is strongly plasticized by water, these relaxation modes have been attributed to localized motions of the polypeptidic chains containing apolar and polar residues, respectively. The deconvolution of the beta-mode by fractional polarization gives the experimental distribution of the dielectric relaxation times of the three materials, and allows us to deduce the activation parameters of each elementary process. These analyses shows the existence of compensation phenomena between the activation parameters, implying cooperative mechanisms. The occurrence of these phenomena with their characteristic parameters are used to specify the origin of the localized relaxation modes in collagen and elastin, and to assign the specific role of each protein in the aortic valves.

Dielectric characterization of collagen, elastin, and aortic valves in the low temperature range

The validity of the compensation rule is studied for some polyene semiconductors namely, β-apo-8′-carotenal, astacene, and methyl bixin. The value of the activation energy (E) of these semiconductors is varied by adsorbing different vapours and also different amounts of a particular vapour. The adsorbed vapours increase the semiconduction currents of these polyenes by several orders of magnitude with a simultaneous increase in the semiconduction activation energies (E). Such change depends on the chemical nature and also on the amount of a vapour adsorbed. It is observed that these polyene semiconductors follow a three-parameter equation σ(T) = σ0' exp (E/2kT0) exp (–E/2kT) where σ0' and T0, the characteristic or compensation temperature, are constants for a substance. Various methods used for evaluating the semiconduction parameters T0 and σ'0 yield consistent results suggesting a physical basis for the compensation effect. The compensation temperature is found to play an important role in the dark conduction process in these polyene semiconductors.



Die Gultigkeit der Kompensationsregel wird fur einige Polyen-Halbleiter wie β-Apo-8′-carotenal, Astazen und Methylbixin untersucht. Der Wert der Aktivierungsenergie (E) dieser Halbleiter wird durch Adsorption verschiedener Dampfe sowie unterschiedlicher Mengen eines speziellen Dampfes geandert. Die adsorbierten Dampfe erhohen den Halbleiterstrom in diesen Polyenen um einige Grosenordnungen bei gleichzeitigem Anwachsen der Aktivierungsenergie (E) der Halbleitung. Diese Anderung hangt von der chemischen Natur und auch von der Menge des adsorbierten Dampfes ab. Es wird beobachtet, das diese Polyen-Halbleiter eine dreiparametrige Gleichung σ(T) = σ'0 exp (E/2kT) befolgen, wo σ'0 und T0, die charakteristische oder Kompensationstemperatur, Konstanten fur eine Substanz sind. Verschiedene Methoden, die zur Berechnung der Halbleiterparameter T0 und σ'0 benutzt werden, ergeben konsistente Ergebnisse, die auf eine physikalische Grundlage fur den Kompensationseffekt hinweisen. Es wird gefunden, das die Kompensationstemperatur eine wesentliche Rolle bei der Dunkelleitung in diesen Polyen-Halbleitern spielt.

Compensation effect in the electrical conduction process in some polyene semiconductors

The semiconductive properties of a series of naphthyl polyenes of the type R(CHCH)nR where R stands for the naphthyl group and n = 1 to 6 are studied as a function of the adsorption of different vapours. With regard to the value of activation energy (E) in the nitrogen atmosphere, these compounds can be divided into two groups: one where the compounds contain odd number of double bonds and the other with even number of double bonds. In the case of the latter compounds the compensation effect is observed to be valid and the value of the compensation temperature (T0) is almost the same for all these compounds. The results indicate that T0 for the other compounds has a rather high value. Different T0 for the compounds having odd or even number of double bonds suggests a physical basis for the compensation effect which is expected to be related to the molecular and crystalline structure of the compounds.



Die halbleitenden Eigenschaften einer Reihe von Naphtylpolyenen vom Typ R(CHCH)nR, wobei R fur die Naphtylgruppe steht und n = 1 bis 6 ist, werden in Abhangigkeit von der Adsorption verschiedener Dampfe untersucht. Bezuglich des Wertes der Aktivierungsenergie (E) in Stickstoffatmosphare lassen sich diese Verbindungen in zwei Gruppen einteilen: eine, bei der die Verbindung eine ungerade Zahl von Doppelbindungen enthalt, und die andere mit gerader Zahl von Doppelbindungen. Im Falle der letzteren Verbindungen wird beobachtet, das der Kompensationseffekt gilt, und das der Wert der Kompensationstemperatur (T0) fur alle Verbindungen fast derselbe ist. Diese Ergebnisse zeigen, das (T0) fur die anderen Verbindungen einen ziemlich hohen Wert besitzt. Unterschiedliche T0 fur Verbindungen mit ungerader und gerader Zahl von Doppelbindungen weisen auf eine physikalische Grundlage fur den Kompensationseffekt hin, von dem erwartet wird, das er mit der molekularen und kristallinen Struktur dieser Verbindungen verknupftist.

Compensation Effect in the Electrical Conduction Process in a Series of Naphthyl Polyenes

The compensation rule is observed to be valid for the electrical conduction in some thymine and uracil complexes with acridine orange. The semiconduction activation energy of a complex varies with dye condentration. It is shown that at low dye concentration, these semiconducting complexes follow the three parameter equation σ(T) = σ′0 exp (E/2kT0) exp (−E/2kT), where σ′0 and T0 are constant for a particular base, the other notations have their usual meaning. The conductivity is measured both on the high and low temperature sides of T0. Consistent values of σ′0 and T0 are obtained by using various methods of evaluation. These results suggest that the compensation effect has a physical origin.



Fur einige Thymin- und Uracil-Komplexe mit Acridinorange wird beobachtet, das die Kompensationsregel gilt. Die Aktivierungsenergie der Halbleitung eines Komplexes andert sich mit der Farbstoff-Konzentration. Es wird gezeigt, das bei niedrigen Farbstoffkonzentrationen diese halbleitenden Komplexe der Dreiparametergleichung σ(T) = σ′0 exp (E/2kT0) exp (–E/2kT) folgen, wo σ′0 und T0 Konstanten fur eine spezielle Basis sind und die ubrigen Bezeichnungen ihre ubliche Bedeutung haben. Die Leitfahigkeit wird sowohl an der Hoch- als auch an der Tief-temperaturseite von T0 gemessen. Konsistente Werte von σ′0 und T0 werden mit verschiedenen Berechnungsmethoden erhalten. Diese Ergebnisse weisen darauf hin, das der Kompensationseffekt eine physikalische Ursache hat.

T. N. Misra

Papers

Compensation effect in the electrical conduction process in some polyene semiconductors

Compensation Effect in the Electrical Conduction Process in a Series of Naphthyl Polyenes

Compensation effect in the electrical conduction process in some nucleic acid base complexes with acridine orange dye