Intercomparisons of dielectric relaxation, dynamic light scattering, and viscoelastic properties of the local segmental motion in amorphous polymers

1988 ◽  
Vol 21 (10) ◽  
pp. 3030-3038 ◽  
Author(s):  
K. L. Ngai ◽  
S. Mashimo ◽  
G. Fytas
Keyword(s):  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Dielectric Relaxation ◽  
Viscoelastic Properties ◽  
Amorphous Polymers ◽  
Segmental Motion ◽  
Relaxation Dynamic

Microrheology study of semidiluted deoxyribonucleic acid solutions

2010 ◽  
Vol 1277 ◽  
Author(s):  
F. Carvajal ◽  
J. G. Alvarez ◽  
E.R. Macías ◽  
V.V.A. Fernández ◽  
E. Robles-Avila ◽  
...  
Keyword(s):  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Sodium Salt ◽  
Viscoelastic Properties ◽  
Deoxyribonucleic Acid ◽  
Complex Viscosity ◽  
Elastic Behavior ◽  
Acid Solutions ◽  
Plateau Modulus ◽  
Calf Thymus

Linear rheological behavior and Microrheology measurements of sodium salt calf-thymus DNA aqueous solutions as a function of concentration are reported here. The microrheological behavior was obtained by a combination of experimental techniques: mechanical Rheometry and Dynamic light scattering (DLS). The viscoelastic properties of DNA in water as a function of concentration were performed at 20 °C and rheological and microrhelogical curves were performed. The result indicated that for concentrations lower than the entanglement concentration (Ce) the system exhibits a predominantly viscous behavior, whereas for higher concentrations exhibits a predominantly elastic behavior. The plateau modulus (G0) and the zero complex viscosity () follow a power law concentration dependence of the form: and , respectively The microrheology results overlap perfectly in a single line with the mechanical rheology results, extending the time resolution to faster breathing modes

Effect of Different Layer Thicknesses and Boundary Conditions of Confined Liquid Crystal on Dynamics of Director Relaxation: Dynamic Light Scattering Investigations

2003 ◽  
Vol 790 ◽  
Author(s):  
Sarmistha Basu ◽  
Fouad M. Aliev
Keyword(s):  
Liquid Crystal ◽  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Boundary Conditions ◽  
Nematic Phase ◽  
Pore Wall ◽  
Surface Relaxation ◽  
Relaxation Processes ◽  
Slow Process ◽  
Relaxation Dynamic

ABSTRACTDynamic light scattering (DLS) has been used to study the influence of boundary conditions (planar-axial and homeotropic-radial) and layer thickness of liquid crystal (8CB) confined to cylindrical pores on phase transitions and relaxation of director orientational fluctuations. For confined 8CB in the nematic phase two well-defined relaxation processes were observed for both axial and radial orientations of the liquid crystal. The first relaxation is qualitatively associated with bulk-like nematic director fluctuations. The second relaxation (with relaxation time slower than the first one) is most likely due to the fluctuations in the layers nearest the wall surface. In samples with radial boundary conditions, we observed the onset of smectic-A phase order formation on the pore wall even though the rest of the liquid crystal could be in the nematic phase. The influence of pore wall-liquid crystal interactions on the properties of the confined 8CB was stronger for radial boundary conditions of confined liquid crystal, than in the case of axial orientation‥ The separation between the first and the second (slow) process was clearer for thinner layers and the amplitude of the slow process was greater for thinner layers. This suggests that the slow process was related to surface relaxation of director fluctuations.

Identification of Different Modes of Molecular Motion in Polymers That Cause Thermorheological Complexity

1995 ◽  
Vol 68 (3) ◽  
pp. 376-434 ◽  
Author(s):  
K. L. Ngai ◽  
D. J. Plazek
Keyword(s):  
Temperature Dependence ◽  
Polymer Chain ◽  
Viscoelastic Properties ◽  
Amorphous Polymers ◽  
Glass Temperature ◽  
Segmental Motion ◽  
Coupling Theory ◽  
Theoretical Understanding ◽  
Chain Dynamics ◽  
The Many

Abstract The viscoelastic properties of amorphous polymers are reviewed with emphasis on the glass to rubber dispersion (often referred to as the transition zone). Deviations from thermorheologieal simplicity (where molecular retardation and relaxation mechanisms have the same temperature dependence) are identified. Most theories and models of polymer chain dynamics do not address or acknowledge thermorheological complexities and correlations, such as that between the temperature dependence and the breadth of viscoelastic and dielectric dispersions of the local segmental motion. Without successful theories of these phenomena the understanding of polymer chain dynamics must be considered incomplete. In this review, old and new experimental data are used to identify the different modes of molecular motions and the domains of their contributions to the time and frequency dependence of the mechanical response of amorphous polymers. The different modes are then shown generally to have their own dependence on temperature. Thus the viscoelastic spectrum, including local segmental motions which dominate the onset of glassy behavior and largely determine the glass temperature, Tg, the glass to rubber softening dispersion, the rubbery plateau and the terminal zone, is thermorheologically complex. A coupling theory, with the physics of intermolecular interactions and cooperativity built into it, describes well the many-body dynamics of densely packed molecular systems such as polymers. The many predictions of the coupling theory are applied to the different viscoeleatic modes to explain the observed anomalous experimental facts and established correlations. The theoretical understanding has been improved to the extent that now a connection can be made between the chemical structure of the monomer and the viscoelastic properties of the polymer.

Dynamic light scattering from gels in a poor solvent

1978 ◽  
Vol 39 (9) ◽  
pp. 955-960 ◽  
Author(s):  
E. Geissler ◽  
A.M. Hecht
Keyword(s):  
Light Scattering ◽  
Dynamic Light Scattering ◽  
Poor Solvent
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