How Dilute are Dilute Solutions in Extensional Flows?

Submitted to J. Rheol.We investigate the concentration-dependence of the characteristic relaxation time of dilute polymer solutions in transient uniaxial elongational flow. A series of monodisperse polystyrene solutions of five different molecular weights (1.8×10^6 ≤ M ≤ 8.3×10^6 g/mol) with concentrations spanning five orders of magnitude were dissolved in two solvents of differing solvent quality (diethyl phthalate and oligomeric styrene). Optical measurements of the rate of filament thinning and the time to break-up in each fluid are used to determine the characteristic relaxation time. A lower sensitivity limit for the measurements was determined experimentally and confirmed by comparison to numerical calculations. Above this sensitivity limit we show that the effective relaxation time of moderately dilute solutions (0.01 ≤ c/c* ≤ 1) in transient extensional flow rises substantially above the fitted value of the relaxation time extracted from small amplitude oscillatory shear flow and above the Zimm relaxation time computed from kinetic theory and intrinsic viscosity measurements. This effective relaxation time exhibits a power-law scaling with the reduced concentration (c/c*) and the magnitude of the exponent varies with the thermodynamic quality of the solvent. This scaling appears to be roughly consistent to that predicted when the dynamics of the partially elongated and overlapping polymer chains are described within the framework of blob theories for semi-dilute solutions.NASA Microgravity Fluid Dynamic

Chaotic flow and efficient mixing in a micro-channel with a polymer solution

Microscopic flows are almost universally linear, laminar and stationary because Reynolds number, $Re$, is usually very small. That impedes mixing in micro-fluidic devices, which sometimes limits their performance. Here we show that truly chaotic flow can be generated in a smooth micro-channel of a uniform width at arbitrarily low $Re$, if a small amount of flexible polymers is added to the working liquid. The chaotic flow regime is characterized by randomly fluctuating three-dimensional velocity field and significant growth of the flow resistance. Although the size of the polymer molecules extended in the flow may become comparable with the micro-channel width, the flow behavior is fully compatible with that in a table-top channel in the regime of elastic turbulence. The chaotic flow leads to quite efficient mixing, which is almost diffusion independent. For macromolecules, mixing time in this microscopic flow can be three to four orders of magnitude shorter than due to molecular diffusion.Comment: 8 pages,7 figure

(1,3)(1,4)-beta-Glucane, Entwicklung eines neuen Sol-Gel-Übergangsmechanismus“

Das wasserlösliche (1,3)(1,4)-beta-Glucan tritt in der Natur als Zellwandbestandteil von Gersten- und Hafersamen, Lichenan (Islandmoos) und Hefen (Saccharomyces Cerevisiae) auf. Das im Endosperm der Braugerste vorhan-dene (1,3)(1,4)-beta-Glucan wird während des Maisch- und Brauvorganges nicht vollständig von den endogenen Enzymen der Gerste abgebaut und neigt, insbesondere in der Lagerperiode bei tiefen Temperaturen, zur Bildung eines Gels, das bei der abschließenden Filtration zu Problemen führen kann, da es die Filter verstopft. Für die Brauereien bedeuten die meist unvorhersehbar auftretenden Filterverstopfungen wirtschaftliche Einbußen, da der Bierausstoß vermindert ist und das zum Filtrieren verwendete Kieselgur weit häufiger als normal ausge-tauscht werden muß. Zur Untersuchung dieses Gelierverhaltens wurde das -Glucan aus dem Bier isoliert und der Aufbau und die Struktur polymeranalytisch umfassend untersucht. Anschließend wurden die Eigenschaften des Gels, insbeson-dere die Gelbildung aus konzentrierten und verdünnten -Glucanlösungen unter verschiedenen Beanspruchun-gen mit rheologischen Untersuchungsmethoden bestimmt.status: publishe

The Non-Linear Flow Properties of Snail Mucus

Biopolymers in aqueous solution have a wide range of applications as their highly tailored designs lead to sophisticated material properties [1] for the daily fight of survival. Snails employ a unique combination of polysaccharides and proteins to produce a mucus with material properties that allow for the stunning capability to crawl on vertical walls or even overhead without loosing contact to the surface. In this paper we present rheological investigations [2] of the material properties of minute amounts of mucus under nonlinear deformation conditions as they are created under the snail foot. For this purpose we present a new technique [3] that enables the investigation in natural film thicknesses of 10 – 20 m. The time and strain-dependent structural changes of the complex mucus gels, presented in the form of Pipkin diagrams [4], show how the deformation of the snail foot exploits the physically-crosslinked structure of the aqueous mucin gels to obtain a maximum adhesion with minimum energy consumption during locomotion. 1. Clasen, C. and W.M. Kulicke, Rheo-optical studies of barley (1 -> 3)(1 -> 4)-beta-glucan solution: Detection of the flow behavior of aggregates in the sol state. Journal of Rheology, 2003. 47(2): p. 321-335. 2. Clasen, C. and W.M. Kulicke, Determination of viscoelastic and rheo-optical material functions of water-soluble cellulose derivatives. Progress in Polymer Science, 2001. 26(9): p. 1839-1919. 3. Clasen, C. and G.H. McKinley, Gap-Dependent Microrheometry of Complex Liquids. Journal of Non-Newtonian Fluid Mechanics, 2004. 124: p. 1-10. 4. Pipkin, A.C., Lectures on Viscoelasticity Theory. 1972, Heidelberg: Springer-Verlag.status: publishe

Viscous and elastic properties of water-soluble cellulosic derivatives regarding to application

Cellulose derivatives as an example for water soluble polymers from renewable resources have gained great importance for the industrial application over the last years. However, the flow property profile of aqueous solutions of cellulose derivatives is not only depending on the chemical composition and substitution pattern, solvent, temperature and concentration but also on the molar mass and the particle size in solution. A correlation of these structure properties with the shear flow properties like the viscosity yield of a cellulose derivative can be obtained for each homologous derivative series of a specific degree of substitution via empirical relationships as the Mark-Houwink-Sakurada-relationship ([]-M- relationship), the 0-[]-c relationship or the -[]-c and the N1-[]-c relationship for the elastic properties of a solution. The elastic response can also be captured via oscillatory agitation of a sample that yields the moduli and hence the network parameters of the cellulose derivative in solution. However, to fully characterize the flow properties in technically relevant problems, also the elongational properties of a solution need to be determined. Lately it could be shown that this is now possible for aqueous solutions of cellulose derivatives with capillary break-up extensional rheometry (CaBER) experiments [1], which probe the transient behaviour of fluid threads of polymer solutions to extract the transient extensional viscosity and relaxation times to correlate these material functions with others of the rheological cycle and the molar mass and the molar mass distribution (MWD).status: publishe

Characterization of Chitosan by Light Scattering, Rheology and NMR-Spectroscopy

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Detection of aggregate formation in aqueous carboxymethyl cellulose solutions

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