Birefringence of Dilute PS Solutions in Abrupt Contraction Flow

Nguyen, Tuan Q.; Porouchani, Réza; Kausch, H. H.

doi:10.1007/978-3-642-58252-3_8

Cited by 22 publications

(41 citation statements)

References 142 publications

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“…This is a consequence of the increasing molecular elongation of the flexible polymer chains as the external strain is increased and is referred to as strain-hardening or sometimes 'strainstiffening' (Nguyen and Kausch, 1999). This increase in the extensional viscosity is only to be expected if the rate of deformation imposed on the fluid is sufficiently rapid to exceed local relaxation of the chain back towards equilibrium; this criterion is parameterized by the Deborah number of the flow.…”

Section: Strain-hardeningmentioning

confidence: 99%

Ex vivo rheology of spider silk

Kojić

Bico

Clasen

et al. 2006

Journal of Experimental Biology

103

102

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SUMMARY We investigate the rheological properties of microliter quantities of the spinning material extracted ex vivo from the major ampullate gland of a Nephila clavipes spider using two new micro-rheometric devices. A sliding plate micro-rheometer is employed to measure the steady-state shear viscosity of ∼1 μl samples of silk dope from individual biological specimens. The steady shear viscosity of the spinning solution is found to be highly shear-thinning, with a power-law index consistent with values expected for liquid crystalline solutions. Calculations show that the viscosity of the fluid decreases 10-fold as it flows through the narrow spinning canals of the spider. By contrast, measurements in a microcapillary extensional rheometer show that the transient extensional viscosity (i.e. the viscoelastic resistance to stretching) of the spinning fluid increases more than 100-fold during the spinning process. Quantifying the properties of native spinning solutions provides new guidance for adjusting the spinning processes of synthetic or genetically engineered silks to match those of the spider.

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Section: Strain-hardeningmentioning

confidence: 99%

Ex vivo rheology of spider silk

Kojić

Bico

Clasen

et al. 2006

Journal of Experimental Biology

103

102

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“…According to the theory [1][2][3], this phenomenon is effective when shear strain occurring on the macromolecule becomes larger than critical value . The latter is inversely proportional to the maximum relaxation time of the polymer chain τ:…”

Section: Conformational Transitions Of Macromolecules In the Free Flowmentioning

confidence: 99%

“…Here A is a constant close to 1. So the critical conditions for CS-transition apply when ߝሶ τ ≈ mass of the polymer, temperature, and polymer chain flexibility, and can be calculated using one of the equations presented in literature [10][11][12]: (2) Here is the solvent's viscosity, M is the molar mass of the polymer, T is the absolute temperature, k is the Boltzmann constant, α is the constant depending on the polymer nature and solvent quality that varies from 1.5 to 1.8, R go is the radius of the gyration of the macromolecule in the static state, and the Fox-Flory parameter Φ 0 . From combining eq.…”

Section: Conformational Transitions Of Macromolecules In the Free Flowmentioning

confidence: 99%

“…In real life, flow profile is usually characterized with heterogeneity and complexity. That is why various devices were suggested to create a defined flow field of defined type [2,13,14]. The most popular devices are those which produce longitudinal flow gradients, since de Gennes' theory predicted the abrupt CS-transition for this type of flow.…”

Section: Conformational Transitions Of Macromolecules In the Free Flowmentioning

confidence: 99%

“…As the critical value is reached, the solute polymer coil unwinds abruptly because of the hydrodynamic interactions. The de Gennes theory became well recognized, and became the basis for numerous modeling experiments directed at investigating the behavior of polymers in flow [2][3][4][5][6].…”

Section: Introductionmentioning

confidence: 99%

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Flow induced conformational transitions of macromolecules and their effect on chromatographic separations

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Švec

Kanat’eva

2015

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The conformation of macromolecules is significantly affected, both in free flow as well as when flowing in a confined space. These effects play a major role when passing polymer molecules in solution through a porous system such as chromatographic column or membrane. Current theories take into account the conformational changes of polymer molecules caused by flow, and provide a description of the unusual behavior of

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Polymer Degradation and Stabilization

Nguyen¹

2005

Handbook of Polymer Reaction Engineering

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IntroductionMost synthetic plastics and natural polymers are principally constituted of the elements C, H, N, and O, all of which are primary components of organic molecules. As with smaller organic molecules, these atoms are attached by relatively weak covalent bonds that are susceptible to chemical attack, particularly to oxidative degradation. During their potential lifetime, engineering plastics are exposed to diverse environmental factors which can act alone or in combination to adversely affect the initial material properties. These changes generally occur over several years, but can be accelerated or retarded in the presence of internal and external elements temperature, and temperature variations. Environmental factors that contribute to degradation include mechanical stresses, temperature variations, humidity, sunlight, oxygen, atmospheric pollutants, and microbial enzymes. Depending on the structural level at which material changes occur, it is usual to distinguish between physical, physicochemical, and chemical degradation.Physical degradation, commonly known as physical aging, results from changes in the thermodynamic state of the system (temperature, pressure, molar volume) during the daily use of the material. During processing, chains may be oriented and the sample inhomogeneously cooled, resulting in internal stress. With time, the chains have the opportunity to relax from their nonequilibrium conformations to a state of lower free energy. Partly immiscible blends, for instance, can remain in a homogeneous metastable state for an extended period of time. The presence of stress or heat can accelerate the phase separation process. The resultant changes in orientation, free volume, internal stress, crystalline content, and

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Birefringence of Dilute PS Solutions in Abrupt Contraction Flow

Cited by 22 publications

References 142 publications

Ex vivo rheology of spider silk

Ex vivo rheology of spider silk

Flow induced conformational transitions of macromolecules and their effect on chromatographic separations

Polymer Degradation and Stabilization

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