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1

Dielectric Relaxation in Cellulose and its Derivatives

100%

Rachocki A., Markiewicz E., Tritt-Goc J.

Acta Physica Polonica A

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2005

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vol. 108

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issue 1

137-145

EN

The relaxation processes in cellulose, methyl cellulose, hydroxypropyl cellulose, and hydroxypropylmethyl cellulose were studied by dielectric spectroscopy. The dielectric spectra for these polysaccharides were measured in the frequency range from 100 Hz to 1 MHz and in the temperature range from 100 to 450 K. The dielectric relaxation data for cellulose, methyl cellulose, hydroxypropylmethyl cellulose were described by Arrhenius and Eyring equations and interpreted as due to a local motion of chain segments via the glucosidic linkages, so-calledβ-relaxation. The same relaxation process was also determined for the hydroxypropyl cellulose polymer in the temperature range of 240-270 K. At higher temperature in hydroxypropyl cellulose another relaxation mechanism occurs due to the reorientation of the side chain built of a few hydroxypropylene groups. The activation parameters of the observed dielectric relaxation processes were determined.

2

Hydration of Hydroxypropylmethyl Cellulose: Effects of pH and Molecular Mass

100%

Tritt-Goc J., Kowalczuk J., Piślewski N.

Acta Physica Polonica A

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2005

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vol. 108

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issue 1

197-205

EN

Magnetic resonance imaging was used to study the diffusion of a water solution of hydrochloric acid (HCl) and sodium hydrochloride (NaOH) into hydroxypropylmethyl cellulose matrices. Polymer in the form of a cylinder was hydrated in a water solvent of pH = 2, 7, and 12 at 37ºC and monitored at equal intervals with a 300 MHz Bruker AVANCE. The spatially resolved spin-spin relaxations times and spin densities, along with a change in the dimension of the glass core of the polymer were determined for hydroxypropylmethyl cellulose tablets as a function of hydration times. The data showed the effects of the pH solvent and of the molecular mass of the polymer on the swelling process, spin-spin relaxation time, and diffusion of solvent molecules into hydroxypropylmethyl cellulose matrices. The time dependence of the diffusion front, effective T_2, and proton-density ρ analysis clearly indicate a case II diffusion mechanism in the system composed of a water solution of hydrochloric acid (pH = 2) and hydroxypropylmethyl cellulose, whereas in the case of water solutions with pH = 7 and 12 the anomalous and case I diffusion are observed, respectively.

3

Electron Spin Echo Envelope Modulation Analysis of SeO¯_{3} Radical in (NH_{4})_{3}H(SeO_{4})_{2} Single Crystal

88%

Tritt-Goc J., Goslar J., Hilczer W., Hoffmann S., Augustyniak M.

Acta Physica Polonica A

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1993

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vol. 84

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issue 6

1131-1141

EN

A detailed computer analysis of the electron spin echo envelope modulations of SeO_{3} radical in a suitable orientation of (NH_{4})_{3}H(SeO_{4})_{2} single crystal is presented. It was found that the modulations are due to a weak dipolar coupling with nitrogens and protons of the only two neighbouring NH_{4} groups among the five NH_{4} groups surrounding SeO¯_{3} center. Isotropic dipolar coupling constant is 1.7 MHz for nitrogens and 0.9 MHz for protons. It was shown that thermal reorientations of NH_{4} groups observed by NMR have a negligible effect on the electron spin echo envelope modulation pattern but can be responsible for the same value of a^{H}_{iso} for all protons in a NH_{4} group. A good fit obtained between experimental spectra and theoretical calculations assuming nondisturbed crystal geometry indicates a small damage of the crystal by X-rays during the radical center formation.

4

Gelation Process of Toluene-Based bis-Urea in Cyclohexane Studied with Magnetic Resonance Imaging

88%

Tritt-Goc J., Boguszyńska J., Szwaj M., Boutellier L., Jadżyn J.

Acta Physica Polonica A

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2005

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vol. 108

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issue 1

81-87

EN

Magnetic resonance imaging was used for studies of the gelation and swelling processes of toluene-based bis-urea prepared in a form of cylindrical tablet and immersed in cyclohexane. The processes were investigated with the use of Bruker AVANCE (300 MHz) spectrometer equipped with a micro imaging probe head. The images were taken for cyclohexane protons within the bis-urea gel formed around the sample dry core at different intervals of the immersion. The mobility of the solvent molecules was estimated from the spatially resolved distribution of the spin-spin relaxation time T_2 and the spin densitiesρ, calculated on the basis of the images obtained. It was shown that the time-evolution of the thickness of the gel layer can be well described by the power equation with an exponent equal to 0.47 (±0.04), indicating the Fickian nature of the diffusion of cyclohexane molecules.

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Dielectric Relaxation in Cellulose and its Derivatives

Hydration of Hydroxypropylmethyl Cellulose: Effects of pH and Molecular Mass

Electron Spin Echo Envelope Modulation Analysis of SeO¯_{3} Radical in (NH_{4})_{3}H(SeO_{4})_{2} Single Crystal

Gelation Process of Toluene-Based bis-Urea in Cyclohexane Studied with Magnetic Resonance Imaging