Transient Viscosity and Molecular Order of a Thermotropic Polyester LCP in Uniaxial Elongational Flow

Light microscopy is a convenient technique for characterizing molecular order in fluid liquid crystalline materials. Microstructures can usually be observed under the actual conditions that promote the formation of liquid crystalline phases, whether or not a solvent is required, and at temperatures that can range from the boiling point of nitrogen to 600°C. It is relatively easy to produce specimens that are sufficiently thin and flat, simply by confining a droplet between glass cover slides. Specimens do not need to be conducting, and they do not have to be maintained in a vacuum. Drybox or other controlled environmental conditions can be maintained in a sealed chamber equipped with transparent windows; some heating/ freezing stages can be used for this purpose. It is relatively easy to construct a modified stage so that the generation and relaxation of global molecular order can be observed while specimens are being sheared, simulating flow conditions that exist during processing. Also, light only rarely affects the chemical composition or molecular weight distribution of the sample. Because little or no processing is required after collecting the sample, one can be confident that biologically derived materials will reveal many of their in vivo structural characteristics, even though microscopy is performed in vitro.

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13C NMR investigations and molecular order of nematogens with biphenyl and bithiophene at terminus

Liquid Crystals ◽

10.1080/02678292.2021.1883139 ◽

2021 ◽

pp. 1-15

Author(s):

A. A. Boopathi ◽

T. Bhavani ◽

Nitin P. Lobo ◽

T. Narasimhaswamy

Keyword(s):

13C Nmr ◽

Molecular Order

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A Continuous Lubricated Squeezing Flow Technique to Study the Rheological Behavior of Polymer Melts in Equibiaxial Elongational Flow

10.1063/1.2964510 ◽

2008 ◽

Author(s):

David Venerus ◽

Teresita Guadarrama-Medina ◽

Tai-Yi Shiu ◽

Albert Co ◽

Gary L. Leal ◽

...

Keyword(s):

Rheological Behavior ◽

Polymer Melts ◽

Elongational Flow ◽

Squeezing Flow ◽

Lubricated Squeezing Flow

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Shear degradation resistance of star poly(ethyleneimine) - polyacrylamides during elongational flow

e-Polymers ◽

10.1515/epoly.2011.11.1.86 ◽

2011 ◽

Vol 11 (1) ◽

Cited By ~ 4

Author(s):

Ming Duan ◽

Shenwen Fang ◽

Liehui Zhang ◽

Fuxiao Wang ◽

Peng Zhang ◽

...

Keyword(s):

Shear Rate ◽

Aqueous Solutions ◽

Relative Viscosity ◽

Reduction Rate ◽

Elongational Flow ◽

Exponential Dependence ◽

Distilled Water ◽

Shear Stability ◽

Low Viscosity ◽

Shear Degradation

AbstractAn experimental study of the flow-induced scission behaviour of four star hydrolyzed polyacrylamides (HPMA) with different arms during planar elongational flow in a cross-slot flow cell is described. The results showed that the shear stability of linear HPAM in distilled water was not essentially different from star HPAM. Polymer scission was not observed in either system in a shear rate range from 20,000 to 100,000s-1, which can be attributed to the strong polyelectrolyte behaviour of HPAM in distilled water. However, at the same shear rate, the star HPAMs exhibited superior shear stability in comparison to the linear HPAMs in aqueous solutions containing NaCl (CNaCl=0.2-1.0%wt) and, in particular, the initial reduction rate of relative viscosity (R) decreased with the degree of branching of the HPAMs. In addition, it was found that the R of five HPAMs in NaCl aqueous solutions exhibited an exponential dependence on shear rate, in which the coefficient C1 can be used to quantitatively evaluate shear stability. In star HPAM NaCl aqueous solutions, the increase of R with shear rate is very likely due to the decrease of the hydrodynamic radius (Rh) of these HPAMs, while the increase of R with NaCl concentrations can be attributed to the relatively low viscosity of these polymers at high NaCl concentrations.

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