1,720,970 research outputs found
ON THE INTRINSIC-VISCOSITY OF ANIONIC AND NONIONIC RODLIKE POLYSACCHARIDE SOLUTIONS
No full textThe ionic strength dependence of intrinsic viscosity as a function of molecular weight was observed substantially for the anionic xanthan polyelectrolyte, while the intrinsic viscosity of nonionic schizophyllan does not change with ionic strength. Ultrasonic degradation was applied as the best mean of obtaining polymer fractions of different molecular weights. It is true, as expected, that schizophyllan has a more rigid triple helix backbone than that of xanthan. As the molecular weight increases, the extension coefficient epsilon of the xanthan chain with ionic strength is found empirically to increase by order 1,48 of molecular weight. Using the Yamakawa-Fujii theory for worm-like chains, both the persistence length q and the contour length L(c) were determined from the best fit of the experimental data of intrinsic viscosity for different ionic strengths to the theoretical curves. The stiffness parameter was established from the ratio of the Kuhn statistical segment length (i. e., twice the persistence length) to the contour length. As the molecular weight decreases, stiff chains of short degraded xanthan become rodlike, while they become gradually worm-like with increasing molecular weight. It also can be seen that the chain stiffness depends on the ionic strength
Dynamic Behavior and Fractional Analysis of Dilute Rigid Polymers Using Packed Hydrodynamic Chromatography
No full textColloidal Force Contributions to the Concentration Depleted Layer Effects in Capillart Flow of Rodlike Particles
No full textEffect of Colloidal Forces on Packed Hydrodynamic Chromatography and Fractional Analysis of Anisotropic Polymers
No full textEstimation of zeta potential by electrokinetic analysis of ionic fluid flows through a divergent microchannel
No full textThe streaming potential is generated by the electrokinetic flow effect within the electrical double layer of a charged solid surface. Surface charge properties are commonly quantified in terms of the zeta potential obtained by computation with the Helmholtz-Smoluchow ski (H-S) equation following experimental measurement of streaming potential. In order to estimate a rigorous zeta potential for cone-shaped microchannel, the correct H-S equation is derived by applying the Debye-Huckel approximation and the fluid velocity of diverging flow on the specified position. The present computation provides a correction ratio relative to the H-S equation for straight cylindrical channel and enables us to interpret the effects of the channel geometry and the electrostatic interaction. The correction ratio decreases with increasing of diverging angle, which implies that smaller zeta potential is generated for larger diverging angle. The increase of Debye length also reduces the correction ratio due to the overlapping of the Debye length inside of the channel. It is evident that as the diverging angle of the channel goes to nearly zero, the correction ratio converges to the previous results for straight cylindrical channel. (C) 2003 Elsevier Inc. All rights reserved.Korea Science and
Engineering Foundation
Orientation and partitioning behavior of dilute rodlike polyelectrolyte suspensions within confined slit microchannels
No full textIn the confined space of narrow channels, the behavior of rodlike polyelectrolytes pertaining to anisotropic configuration effect is much different than in the bulk. Based on our previous study, we analyzed on the orientational order of rodlike polyelectrolyte in dilute suspensions under the action of the long-range colloidal interactions, which results in the concentration depletion near the solid surface. For the orientation of rodlike polyelectrolytes existing near the charged wall, the electrostatic repulsive interaction explicitly creates the preferential alignment of rod segments perpendicular to the surface, while the parallel alignment is favored without this interaction. The concentration-depleted layer thickness, in which the perpendicular orientation of the rods is predicted, increases either with decreased solution ionic strength or with increased surface potentials of the wall and the rod. The partition coefficient determined from the concentration profile presents the fact that the rod is more excluded by electrostatic and entropic effects with the increase of confining strength. It is evident that the presence of electrostatic interactions changes the partitioning behavior of rodlike polyelectrolyte suspension in the dilute limit. (C) 2002 Elsevier Science B.V. All rights reserved
THE CORE COLLAPSE OF GLOBULAR-CLUSTERS WITH STELLAR EVOLUTION
No full textThe orbit averaged Fokker-Planck equation is used to study the dynamical evolution of globular clusters. Stellar evolutions according to their masses are incorporated in the model. The initial density distribution is chosen by Plummer's model with the initial mass function index alpha = 0.65, 1.35,2.35, and 3.35. The mass-loss rate is given by the model of Fusi-Pecci and Renzini. It is found that the stellar mass loss acts as an energy source, and thereby affects the dynamical evolution of globular clusters by slowing down the evolution rate and extending the core collapse time. Also, the dynamical length scale is extended
CONCENTRATION-DEPLETED LAYERS DUE TO COLLOIDAL FORCE AND ITS INFLUENCE ON THE XANTHAN FRACTIONATION
No full textThis work was supported by Fundamental Research Grant 911-1001-004-2 from the Korea Science and Engineering Foundation. The authors gratefully acknowledge financial support from the KOSEF
ANALYSIS ON THE APPARENT SLIP AND DEPLETED LAYER OF POLYMER FLOW IN NARROW-BORE CAPILLARIES
No full textPolymer solutions flowing through small-diameter capillaries of which length scale is much larger than that of polymers were experimentally demonstrated to have the enhanced flow rate as compared to in bulk flow. This apparent slip phenomenon was analyzed by obtaining the slip velocity and concentration depleted layer thickness. Hydrolyzed polyacrylamide (HPAM) of highly flexible polymer and Xanthan of rigid rodlike polymer were made to flow through stainless steel capillaries having the diameter range of about 100 to 250 mum. The results showed that both slip velocity and depleted layer thickness decreased markedly with increasing polymer concentration. This behavior can be interpreted as being due to the reduction of diffusion coefficient and flexibility of polymer chains as the concentration is increased. The depleted layer thickness of HPAM was much larger than the polymeric length scale and was shown to increase with increasing wall shear stress. This is considered as an evidence of the stress-induced diffusion of polymer chains being a dominant factor for the apparent slip of flexible polymer solution. On the other hand, the depleted layer thickness of Xanthan solution was almost constant with the wall shear stress, which can not be explained by the stress-induced diffusion mechanism alone
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