The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform
Bjorn E Christensen - One of the best experts on this subject based on the ideXlab platform.
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a study of the chain stiffness and extension of alginates in vitro epimerized alginates and periodate oxidized alginates using size exclusion chromatography combined with light scattering and viscosity detectors
Biomacromolecules, 2006Co-Authors: Inger M N Vold, Kare Andre Kristiansen, Bjorn E ChristensenAbstract:A series of alginates isolated from the stem and leaf of a brown algae (Laminaria hyperborea), bacterial mannuronan, in vitro epimerized mannuronans, and periodate oxidized alginates were analyzed by size-exclusion chromatography (SEC) combined with online multiangle laser light scattering (MALS) and Viscometry (collectively abbreviated SMV). Selected samples were also analyzed off-line using low-angle laser light scattering and capillary Viscometry. Excellent agreement between the two methods was obtained for properly purified samples. In contrast, abnormal results were obtained for some industrial samples due to the presence of particulate material. Naturally occurring alginates and in vitro epimerized mannuronans were found to obey essentially the same RG−M and [η]−M relations, and hence, the same Mark−Houwink−Sakurada (MHS) equations (valid for I = 0.10 M): 20 000 g/mol < M < 100 000 g/mol, [η] = 0.0054 ·M1.00; 100 000 g/mol < M < 1 000 000 g/mol, [η] = 0.071 ·M0.89. Application of the wormlike chain...
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macromolecular characterisation of three barley β glucan standards by size exclusion chromatography combined with light scattering and Viscometry an inter laboratory study
Carbohydrate Polymers, 2001Co-Authors: Bjorn E Christensen, A S Ulset, Michael Beer, B E Knuckles, D L Williams, Marshall L Fishman, Hoa K Chau, Peter J WoodAbstract:Abstract Six (1→3)(1→4)-β- d -glucan standards (A–F) isolated from barley were analysed by size-exclusion chromatography (SEC) in five different laboratories with varying columns, solvent conditions and detector systems (low- and multi-angle light scattering and Viscometry). Static (batch) measurements by capillary Viscometry and laser light scattering were included. Fairly consistent results were obtained for the weight average molecular weights (Mw), radii of gyration (RG) and intrinsic viscosities [η], demonstrating that the β-glucans may serve as useful standards or reference materials in the study of cereal β-glucans. Average values for Mw were: A,E: 114,000 (±11%); B,C: 374,000 (±9%), D,F: 228,000 (±13%). Some inconsistencies regarding the polydispersity (Mw/Mn) could be ascribed to the influence of peak broadening in certain column/solvent systems. The study further demonstrated that individual researchers tended to use different processing parameters, especially refractive index increments (dn/dc), due to ambiguities in the literature or to differing experimental values. The need for consistent parameters and processing methods is clearly demonstrated.
Leong Y Yeow - One of the best experts on this subject based on the ideXlab platform.
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obtaining the shear rate function and the slip velocity function from couette Viscometry data
Journal of Non-newtonian Fluid Mechanics, 2004Co-Authors: Leong Y Yeow, Belinda Choon, Lena Karniawan, Lanny SantosoAbstract:Abstract The equation that relates the rotational speed to the wall shear stresses in Couette viscometers is treated as an integral equation of the first kind for the unknown shear stress versus shear rate function and the wall shear stress versus slip velocity function. A method, based on Tikhonov regularization, is used to obtain approximate solutions of these two material property functions simultaneously. To determine the slip velocity function data from two or more Couette viscometers with different radii are required but, unlike existing methods, there are no restrictions on the radius ratios of these viscometers. This way of processing Couette Viscometry data also does not require the functional forms of the material functions to be prescribed. The built-in regularization parameter of Tikhonov regularization keeps noise amplification under control giving material property functions that are relatively free of spurious fluctuations. The performance of this method of treating Couette Viscometry data is demonstrated by applying it to a number of data sets taken from the published literature.
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a new method of processing capillary Viscometry data in the presence of wall slip
Journal of Rheology, 2003Co-Authors: Leong Y Yeow, Hok L Lee, Ajay R Melvani, Greg C MifsudAbstract:The problem of converting capillary Viscometry data with wall slip into a shear stress versus shear rate relationship and a wall shear stress versus slip velocity relationship is formulated as an integral equation of the first kind. This reveals the ill-posed nature of the problem. A procedure based on Tikhonov regularization is applied to find an approximate solution to this equation. This way of processing capillary Viscometry data has the advantage that it does not require the assumption of a rheological model to relate the shear rate and the slip velocity to the local shear stress. Since Tikhonov regularization allows for the ill-posed nature of the problem, it can be expected to give reliable results in the presence of experimental noise. The performance of this method is demonstrated by applying it to the capillary data for a linear low-density polyethylene, a high-density polyethylene, a suspension of ammonium sulfate particles in a viscous Newtonian carrying fluid, and a mineral-based aqueous paper coating color. In each case, Tikhonov regularization has succeeded in obtaining the maximum amount of information regarding the rheological properties of the material and these properties are in good or reasonable agreement with published data.
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solving the inverse problem of couette Viscometry by tikhonov regularization
Journal of Rheology, 2000Co-Authors: Leong Y Yeow, Pannie P P TangAbstract:Most of the existing procedures for converting Couette Viscometry data into a shear stress τ versus shear rate γ material function rely on the small annular gap assumption or require the algebraic form of the τ–γ curve to be prespecified. Furthermore most of the existing procedures are not particularly suitable for fluids with yield stress. In this investigation the problem of converting Couette Viscometry data into a τ–γ material function is formulated as a Volterra integral equation of the first kind. A method based on Tikhonov regularization is then developed to solve this equation for the τ–γ curve. The method does not depend on the small gap assumption or require prespecification of the algebraic form of the τ–γ relationship. It is equally applicable to fluids with and without yield stress. For fluids with yield stress, provided the data include one or more points where the fluid in the annular gap is partially sheared, the method will also extract the yield stress from the data. The performance of this general method is demonstrated by applying it to synthetic Couette Viscometry data with added random noise and to experimental data taken from the literature.
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processing the capillary Viscometry data of fluids with yield stress
Rheologica Acta, 2000Co-Authors: Leong Y Yeow, Yen T Nguyen, Hay K WongAbstract:The capillary viscometer is used to measure the shear stress-shear rate relationship of a wide range of purely viscous fluids. It is however not considered as an appropriate instrument for obtaining the yield stress and the post-yield behaviour of fluids that have a yield stress. This is partly because conventional methods of processing the capillary Viscometry data of purely viscous fluids cannot be applied to similar data of fluids with yield stress. The unavoidable experimental noise in the capillary data, particularly at low shear rates, also makes it difficult to obtain a reliable estimate of the yield stress from capillary data. In this investigation the problem of converting the capillary Viscometry data of yield stress fluids into a shear stress-shear rate curve and a yield stress is formulated as a Volterra integral equation of the first kind. This is an ill-posed problem i.e. noise in the data will be amplified by inappropriate methods of data processing. A method, based on Tikhonov regularisation that takes into account the ill-posed nature of the problem, is then developed to solve this problem for fluids with yield stress. The performance of this method is assessed by applying it to a set of “synthetic” capillary Viscometry data with added random noise and to a set of experimental data for a concentrated suspension of TiO2 taken from the literature. In both cases Tikhonov regularisation was able to extract the complete shear properties of these fluids from capillary Viscometry data alone.
Micha Peleg - One of the best experts on this subject based on the ideXlab platform.
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squeezing flow Viscometry for nonelastic semiliquid foods theory and applications
Critical Reviews in Food Science and Nutrition, 2002Co-Authors: Osvaldo H Campanella, Micha PelegAbstract:In most conventional rheometers, notably the coaxial cylinders and capillary viscometers, the food specimen is pressed into a narrow gap and its structure is altered by uncontrolled shear. Also, most semiliquid foods exhibit slip, and consequently the measurements do not always reflect their true rheological properties. A feasible solution to these two problems is squeezing flow Viscometry where the specimen, practically intact and with or without suspended particles, is squeezed between parallel plates. The outward flow pattern mainly depends on the friction between the fluid and plates or its absence ("lubricated squeezing flow"). Among the possible test geometries, the one of constant area and changing volume is the most practical for foods. The test can be performed at a constant displacement rate using common Universal Testing Machines or under constant loads (creep array). The tests output is in the form of a force-height, force-time, or height-time relationship, from which several rheological parameters can be derived. With the current state of the art, the method can only be applied at small displacement rates. Despite the method's crudeness, its results are remarkably reproducible and sensitive to textural differences among semiliquid food products. The flow patterns observed in foods do not always follow the predictions of rheological models originally developed for polymer melts because of the foods' unique microstructures. The implications of these discrepancies and the role that artifacts may play are evaluated in light of theoretical and practical considerations. The use of squeezing flow Viscometry to quantify rheological changes that occur during a product's handling and to determine whether they are perceived sensorily is suggested.
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Imperfect lubricated squeezing flow Viscometry for foods
Rheologica Acta, 1997Co-Authors: Bernhard Hoffner, Christian Gerhards, Micha PelegAbstract:Commercial mayonnaise and mustard samples placed in a wide, shallow Teflon container were compressed by a wide Teflon plate to induce an ‘imperfect’ lubricated squeezing flow. A dominant squeezing flow regime could be clearly identified as a linear region in the log F(t) vs log H(t) relationship, F(t) and H(t) being the momentary force and specimen height respectively. The slope of the relationship enabled the estimation of the flow index, n , and the consistency coefficient K . The n values of the mayonnaise were on the order of 0.6–0.85 and those of the mustard about 0.7. The corresponding K values were on the order of 6–13 and 4–5 kPas^n respectively. Considering the crudeness of the array the measurements were highly reproducible and sensitive enough to detect differences (mayonnaise) or establish similarities (mustard) in products of different brands. The calculated flow index was practically independent of the plate's radius and of the consistency coefficient, which had a weak dependency on the latter. The calculated elongational viscosity vs biaxial strain rate relationship could also be used to compare the different products and brands. At 0.01 s^−1 the elongational viscosity of the maynonnaise was on the order of 150 kPas, and of the mustard 60 kPas.
Tatsuya Shimoda - One of the best experts on this subject based on the ideXlab platform.
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characterization of polydihydrosilane by sec malls and Viscometry
Polymer, 2012Co-Authors: Takashi Masuda, Yasuo Matsuki, Tatsuya ShimodaAbstract:Abstract Silicon hydride compounds consisting of silicon and hydrogen constitute a fascinating class of silicon-based polymers because of their ability to form high-quality silicon film by solution-based process. In this study, we synthesize polydihydrosilane by photo-induced ring-opening polymerization of cyclopentasilane, and determine the molar mass, radius of gyration, and intrinsic viscosity of it in cyclohexene by size-exclusion chromatography combined with multi-angle laser light scattering and Viscometry. It was found that the molar mass of polydihydrosilane ranges broadly from 102 to 106 g/mol. Both the intrinsic viscosity and radius of gyration exhibited a scaling behavior with respect to the molar mass with the intrinsic viscosity exponent α = 0.206 and radius of gyration exponent ν = 0.410. Classification of the polymer structure based on the α value suggests that the polydihydrosilane forms a branched-chain structure with a particle-like compact shape rather than a straight chain.
Ljubica Dokić - One of the best experts on this subject based on the ideXlab platform.
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Application of different techniques in the determination of xanthan gum-SDS and xanthan gum-Tween 80 interaction
Food Hydrocolloids, 2019Co-Authors: Veljko Krstonošić, Maja Milanovic, Ljubica DokićAbstract:Abstract Polymer - surfactant aqueous systems are important for a variety of industrial applications. The properties of those systems among other depend on the interactions between them. The aim of this work was to determine interactions between anionic polymer - xanthan gum and anionic surfactant - SDS or nonionic surfactant - Tween 80. In order to get better insight into the occurrence and possible mechanism of interactions several techniques were used such as FTIR, Viscometry, conductometry, tensiometry, fluorimetry as well as SEM analysis. The results obtained by the combination of all those techniques showed that xanthan gum – SDS/Tween 80 interactions existed. Structural changes of xanthan gum molecules in presence of both surfactants were obtained by Viscometry and SEM. The characteristic interaction points (CAC and PSP) were determined by measuring surface tension and specific conductance of pure surfactant aqueous solutions and their mixtures with xanthan gum. The values of PSP were proportional to the polymer concentration. After overcoming electrostatic repulsion between xanthan gum and SDS, they form complexes through hydrophobic mechanism and enhance adsorption of SDS molecules at the water – air interface. Unlike SDS, Tween 80 mainly interacts with xanthan gum in the bulk creating hydrogen bonds as well as by hydrophobic interactions. The results of fluorescence measurements expressed as I1/I3 ratio additionally confirmed that the mechanism of interactions between xanthan gum and examined surfactants was mainly through hydrophobic interaction and by creation the hydrogen bonds with Tween 80 as through electrostatic repulsion with SDS.
