Rheology, polysaccharides

Viscosity is the resistance presented by a liquid to external forces subjecting it to flow. Laminar flow only is considered in polysaccharide rheology - as the name implies, the velocity in laminar flow increases monotonically with distance away from the edge of the vessel, pipe, etc. (in turbulent flow the flow rate will have local maxima and minima) (Figure 4.26). Imagine two hypothetical plates parallel to the direction of flow and the sides of the container, separated vertically by a distance 5x. One plate will be moving faster than the plate below it and will experience a force F because of viscous forces. This force will be in proportional to the area of the plane, so we can define a sheer stress of FjA, where A is the area of the plate. The force will bring about a difference of velocity 8v between two adjacent plates separated by 8x and we can define a sheer strain rate, usually denoted y, as 8v/8x, in the limit dv/dx (with dimensions of Kinetic or dynamic viscosity, t, is defined by eqn. (4.10) and... 

The search for a low-cost, effective mobility control agent is currently focused on dilute aqueous solutions containing partially hydrolyzed polyacrylamides or polysaccharides. Rheological properties have been studied, including the effects of polymer concentration, shear rate, electrolyte concentration, and type of electrolyte. 

Starches. Starch (qv) granules must be cooked before they wiU release their water-soluble molecules. It is common to speak of solutions of polysaccharides, but in general, they do not form tme solutions because of their molecular sizes and intermolecular interactions rather they form molecular dispersions. The general rheological properties of polysaccharides like the starch polysaccharides are described below under the discussion of polysaccharides as water-soluble gums. Starch use permeates the entire economy because it (com starch in particular) is abundantly available and inexpensive. Another key factor to its widespread use is the fact that it occurs in the form of granules. 

In this system, the high molecular weight polysaccharide polymer, is used to extend the rheological properties of bentonite. 

The rheological behavior of storage XGs was characterized by steady and dynamic shear rheometry [104,266]. Tamarind seed XG [266] showed a marked dependence of zero-shear viscosity on concentration in the semi-dilute region, which was similar to that of other stiff neutral polysaccharides, and ascribed to hyper-entanglements. In a later paper [292], the flow properties of XGs from different plant species, namely, suspension-cultured tobacco cells, apple pomace, and tamarind seed, were compared. The three XGs differed in composition and structural features (as mentioned in the former section) and... 

In a current rheological study [296], the galactoxyloglucan from Hymenia courbaril was mixed with starch containing 66% amylose and with waxy corn starch (amylopectin). The gel mixtures showed, under static rheological conditions, an increase in paste viscosity compared to those of the polysaccharides alone. Dynamic rheometry indicated that the interactions resulted in increased thermal stability of the gel formed in comparison to that of the starch alone. 

Lapasin R, Pricl S (1995) Rheology of Industrial Polysaccharides. Theory and Applications. Blackie, London... 

Oil-field chemistry has undergone major changes since the publication of earlier books on this subject Enhanced oil recovery research has shifted from processes in which surfactants and polymers are the primary promoters of increased oil production to processes in which surfactants are additives to improve the incremental oil recovery provided by steam and miscible gas injection fluids. Improved and more cost-effective cross-linked polymer systems have resulted from a better understanding of chemical cross-links in polysaccharides and of the rheological behavior of cross-linked fluids. The thrust of completion and hydraulic fracturing chemical research has shifted somewhat from systems designed for ever deeper, hotter formations to chemicals, particularly polymers, that exhibit improved cost effectiveness at more moderate reservoir conditions. 

Stabilizing agents are used to maintain drilling fluid rheological properties at highly elevated downhole temperatures. Chromium and chromium-free lignosulfonates, polyglycol ethers, sodium polystyrene sulfonate-co-maleic anhydride), and a melanin polymer have been used in this application. Additives such as sodium diethyldi-thiocarbamate have been used to stabilize aqueous polysaccharides such as xanthan gum (18). 

The main function of the foam stabilising agent is to reinforce the intercellular film wall by contributing rheological characteristics of viscoelasticity. The increased viscosity may also assist handling. The aim, as so often with auxiliaries, is to achieve an optimum balance. If the bubbles are too thin and wet too quickly they will collapse prematurely, whilst too stable a film could hinder uniform application. Examples of products used as foam stabilisers include thickening agents such as the polysaccharides, hydroxyethylcellulose, methylcellulose,... 

N djouenkeu R, Goycoolea FM, Morris ER, Akingbala JO. Rheology of okra (Hibiscus esculentus L.) and dika nut (Irvingia gabonensis) polysaccharides. Carbohydr Polym 1996 29 263-269. 

Emphasis in the initial phase of our work was placed on sulfated polysaccharides that are antiviral. Not only were the desired rheological properties and long-term stability achieved in DCE formulations, the activity of the dextran sulfate or N9 were not compromised. DCE formulations containing DS display strong anti-HIV activity in vitro in comparison with negative (not shown) and positive controls (Figure 2). This is an important first step in the screening process towards clinical effectiveness. 

Dickinson, E. (1998). Stability and rheological implications ofelectrostatic milk protein-polysaccharide interactions. Trends Food Sci. TechnoL, 9, 347-354. 

Indeed, at very high polymer concentrations enhancement of these effects occurs. Recent studies by Franks et al. 23) on the rheological behaviour and freeze fracture electron microscopical analysis of several synthetic linear flexible polymers, including poly(vinylpyrrolidone) and polyethylene glycol) in concentrated solutions, suggest that these molecules do not form a network mesh but rather exhibit aggregation. Anionic polysaccharides, on the other hand, are known to form an anisotropic packing array in condensed films. These films may be stretched to enhance orientation and be used for X-ray diffraction studies... 

Eylers, J. P. (2008). Mucus and slime Structure and rheology of natural polysaccharides. 

Dickinson, E., Goller, M.I., Wedlock, D.J. (1993). Creaming and rheology of emulsions containing polysaccharide and non-ionic or anionic surfactants. Colloids and Surfaces A Physicochemical and Engineering Aspects, 75, 195-201. 

Grant, J., Cho, J., Allen, C. (2006). Self-assembly and physicochemical and rheological properties of a polysaccharide-surfactant system formed front the cationic biopolymer chitosan and nonionic sorbitan esters. Langmuir, 22,4327- 4335. 

Nowadays it is well established that the interactions between different macromolecular ingredients (i.e., protein + protein, polysaccharide + polysaccharide, and protein + polysaccharide) are of great importance in determining the texture and shelf-life of multicomponent food colloids. These interactions affect the structure-forming properties of biopolymers in the bulk and at interfaces thermodynamic activity, self-assembly, sin-face loading, thermodynamic compatibility/incompatibility, phase separation, complexation and rheological behaviour. Therefore, one may infer that a knowledge of the key physico-chemical features of such biopolymer-biopolymer interactions, and their impact on stability properties of food colloids, is essential in order to be able to understand and predict the functional properties of mixed biopolymers in product formulations. 

Thermodynamically unfavourable interactions between two biopolymers may produce a significant increase in the surface shear viscosity (rf) of the adsorbed protein layer. This change in surface rheological behaviour is a consequence of the greater surface concentration of adsorbed protein. For instance, with p-casein + pectin at pH = 5.5 and ionic strength = 0.01 M (Ay = 2.6 x 10 m3 mol kg-2), the surface shear viscosity at the oil-water interface was found to increase by 20-30%, i.e., rp = 750 75 and 590 60 mN s m-1 in the presence and absence of polysaccharide. These values of rp refer to data taken some 24 hours following initial protein layer formation (Dickinson et al., 1998 Semenova et al., 1999a). 

Surface shear rheology at the oil-water interface is a sensitive probe of protein-polysaccharide interactions. In particular, there is considerable experimental evidence for a general increase in surface shear viscosity of protein adsorbed layers as a result of interfacial complexation with polysaccharides (Dickinson et al., 1998 Dickinson and Euston, 1991 Dickinson and Galazka, 1992 Semenova et al., 1999a Jourdain et al., 2009). One such example is the case of asi-casein + pectin at pH = 5.5 and ionic strength = 0.01 M (Ay = - 334 x 10 cm /mol) the interfacial viscosity after 24 hours was found to be five times larger in the presence of pectin (i.e., values of 820 80 and 160 20 mN m 1 with and without pectin, respectively) (Semenova et al., 1999a). 

Protein-polysaccharide complexation affects the surface viscoelastic properties of the protein interfacial layer. Surface shear rheology is especially sensitive to the strength of the interfacial protein-polysaccharide interactions. Experimental data on BSA+ dextran sulfate (Dickinson and Galazka, 1992), asi-casein + high-methoxy pectin (Dickinson et al., 1998), p-lactoglobulin + low-methoxy pectin (Ganzevles et al., 2006), and p-lactoglobulin + acacia gum (Schmitt et al., 2005) have all demon-... 

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