NMR field-cycling relaxation spectroscopy, transverse NMR relaxation, self-diffusion and zero-shear viscosity: Defect diffusion and reptation in non-glassy amorphous polymers

1982 ◽  
Vol 260 (10) ◽  
pp. 911-936 ◽  
Author(s):  
R. Kimmich ◽  
R. Bachus
Keyword(s):  
Shear Viscosity ◽  
Nmr Relaxation ◽  
Amorphous Polymers ◽  
Zero Shear Viscosity ◽  
Defect Diffusion ◽  
Self Diffusion ◽  
Field Cycling

Prediction of Zero-Shear Viscosity of Linear Polybutadienes from the Crossover Point Using Doi-Edwards Theory

1988 ◽  
Vol 61 (5) ◽  
pp. 812-827 ◽  
Author(s):  
Ramesh R. Rahalkar ◽  
Henry Tang
Keyword(s):  
Shear Viscosity ◽  
Amorphous Polymers ◽  
Simple Expression ◽  
Crossover Frequency ◽  
Crossover Point ◽  
Zero Shear Viscosity ◽  
Plateau Modulus ◽  
Good Agreement

Abstract Based upon the Doi-Edwards theory, a simple expression has been obtained for zero-shear viscosity in terms of the plateau modulus and the crossover frequency. There are no adjustable parameters in the expression. The model is in very good agreement with the zero-shear viscosity values for linear polybutadienes, the typical discrepancy being ∼5–10%. If the model can be validated for other linear amorphous polymers, it may become possible to estimate the zero-shear viscosity by measuring a single Theological parameter (the crossover frequency).

Molecular Dynamics in the Columnar and Lamellar Mesophases of a Liquid Crystal of Biforked Molecules

1996 ◽  
Vol 51 (3) ◽  
pp. 155-166
Keyword(s):  
Molecular Dynamics ◽  
Liquid Crystal ◽  
Nmr Relaxation ◽  
Larmor Frequency ◽  
Smectic Layer ◽  
Self Diffusion ◽  
Relaxation Measurements ◽  
Different Temperatures ◽  
Collective Movements ◽  
Field Cycling

In this work we present the first study of molecular dynamics in the Sc and Փh mesophases of a liquid crystal of biforked molecules. This study was performed by means of proton NMR relaxation measurements obtained at different temperatures in the studied phases, combining standard and fast field-cycling techniques in order to cover a large domain of Larmor frequencies (100 Hz - 300 MHz). The experimental results were analysed considering the potential contributions of different relaxation mechanisms, namely local molecular rotational reorientations, self-diffusion and collective movements. The description of the contributions of the rotational reorientations and self-diffusion mechanisms are not quite different in the two studied phases. The main distinction in the molecular dynamics is found in the low Larmor frequency range dominated by the collective movements. While in the Sc phase this contribution can be described by the law characteristic of smectic layer undulations, the contribution of the collective movements in the Փh phase can be assigned to elastic deformation of the columns.

Dynamics of Wormlike Polymers in Solution:  Self-Diffusion and Zero-Shear Viscosity

2000 ◽  
Vol 33 (26) ◽  
pp. 9630-9640 ◽  
Author(s):  
G. Petekidis ◽  
D. Vlassopoulos ◽  
G. Fytas ◽  
G. Fleischer ◽  
G. Wegner
Keyword(s):  
Shear Viscosity ◽  
Zero Shear Viscosity ◽  
Self Diffusion

Proton NMR Relaxation Study of Molecular Motions in a Liquid Crystal with a Strong Polar Terminal Group

1993 ◽  
Vol 48 (8-9) ◽  
pp. 851-860 ◽  
Author(s):  
P. J. Sebastião ◽  
A. C. Ribeiro ◽  
H. T. Nguyen ◽  
F. Noack
Keyword(s):  
Theoretical Calculations ◽  
Proton Nmr ◽  
Nmr Relaxation ◽  
Larmor Frequency ◽  
Terminal Group ◽  
Relaxation Dispersion ◽  
Proton Relaxation ◽  
Self Diffusion ◽  
Smectic A ◽  
Field Cycling

Abstract Liquid crystalline compounds containing a cyano terminal group often exhibit peculiar molecular organizations of their mesophases. In this work we present proton NMR relaxation studies, performed by means of standard NMR and fast field-cycling NMR techniques, in the nematic (N) and bilayered smectic-A phase (SA2) of 4-pentyl-phenyl 4'-cyanobenzoyloxy-benzoate. The field-cycling measurements were used to clarify the relaxation behaviour in the low Larmor frequency range, where conventional techniques are not applicable. Self-diffusion and rotational reorientations are found to be the essential relaxation mechanisms at MHz frequencies in the smectic mesophase, while the contribution of collective modes appears only at lower frequencies in the kHz range. In the nematic mesophase the order director fluctuations mechanism dominates the relaxation dispersion up to 10 MHz, where the rotational reorientations become important, with minor corrections from the self-diffusion process. The agreement between the experimental findings and model fits could be improved by an additional relaxation mechanism in the kHz regime, ascribed to the interaction between protons and fast relaxing quadrupolar nitrogen 14N nuclei. Though all four processes are present in the nematic and smectic-A2 phases, the overall T1 frequency dependence is quite different in the two cases. This behaviour is discussed in terms of available theoretical calculations of the proton relaxation dispersion in liquid crystals, and it is also compared with data known from other cyano compounds.

Investigation of Molecular Motion in Smectic Phases of the Liquid Crystal TBBA by NMR Relaxation Dispersion

1980 ◽  
Vol 35 (9) ◽  
pp. 924-929 ◽  
Author(s):  
Th. Mugele ◽  
V. Graf ◽  
W. Wülfel
Keyword(s):  
Nmr Relaxation ◽  
Larmor Frequency ◽  
Proton Spin ◽  
Relaxation Dispersion ◽  
Self Diffusion ◽  
Smectic Phases ◽  
Field Cycling ◽  
The Difference ◽  
Nmr Methods ◽  
Fast Field

Abstract The proton spin T1 relaxation dispersion in the smectic A and C phase of TBBA, and for comparison also in the nematic phase, have been studied using time dependent fast field-cycling techniques in the Larmor frequency range from νp = 100 Hz to 44 MHz. Our measurements considerably extend recent ones by Blinc et al., performed with other NMR methods for frequencies ≧ 140 kHz. The new experimental data are consistent with the reported ones for Sm C but not for Sm A, the difference being that the essential T1 dispersion observed with our technique occurs at much lower frequencies, namely below about 100 kHz. As a consequence, the relaxation dispersion for both smectic phases looks very similar. It can be described quantitatively in terms of relaxation by "nematic-like" order fluctuations, self-diffusion, and by a third molecular mechanism with (for simplicity) Debve-like power spectrum, which is possibly a second type of order fluctuation or a molecular rotation about the short axis. The analysis reveals surprisingly far going parallels between the spin relaxation of simple smectics and that of high-temperature nematics like PAA.

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