Solutions flow properties

Graessley W W 1993 Viscoelasticity and flow in polymer melts and concentrated solutions Physical Properties of Polymers ed J E Mark et al (Washington, DC ACS) pp 97- 143... 

The flow properties of sodium alginate solutions depend on concentration. A 2.5% medium viscosity sodium alginate solution is pseudoplastic, especially at the higher shear rates in the range of 10—10,000/s. 

Larch gum is readily soluble in water. The viscosity of these solutions is lower than that of most other natural gums and solutions of over 40% soHds are easily prepared. These highly concentrated solutions are also unusual because of their Newtonian flow properties. Larch gum reduces the surface tension of water solutions and the interfacial tension existing in water and oil mixtures, and thus is an effective emulsifying agent. As a result of these properties, larch gum has been used in foods and can serve as a gum arabic substitute. 

Gum arable comes from various species of Acacia. The gum exudes through cracks, injuries, and incisions in the bark and is collected by hand as dried tears. Gum arable is unique among gums because of its high solubiUty and the low viscosity and Newtonian flow of its solutions. While other gums form highly viscous solutions at 1—2% concentration, 20% solutions of gum arable resemble a thin sugar symp in body and flow properties. 

Higher butyryl esters, formulated with acryUc polymers, provide coatings with excellent weather resistance, good colorfastness and dispersibiUty, and good flow properties (154). Formulations for a typical automotive refinishing lacquer and a wood furniture lacquer are given in Tables 12 and 13, respectively. Low viscosity, high butyryl cellulose esters tolerate substantial amounts of alcohol solvent without appreciable increase in solution viscosity. 

Methods of preparation of the laminates depend on the partieular grade of polyimide resin used but in one process the polyimide precursor is dissolved in acetone and this solution is used to impregnate the glass or carbon fibre and thus produce a pre-preg . The pre-preg is dried and then pre-cured at about 200°C for about 3 hours. This operation reduces the volatile content and also modifies the flow properties to make them more suitable for the subsequent... 

In order to obtain solutions with the desired flow properties, shear-induced degradation should be avoided. From mechanical degradation experiments it has been shown that chain scission occurs when all coupling points are loose and the discrete chains are subjected to the velocity field. Simple considerations lead to the assumption that this is obtained when y) is equal to T sp(c-[r ]) (Fig. 18). The critical shear rate can then easily be evaluated [22]. 

The measurement of viscosity is important for many food products as the flow properties of the material relate directly to how the product will perform or be perceived by the consumer. Measurements of fluid viscosity were based on a correlation between relaxation times and fluid viscosity. The dependence of relaxation times on fluid viscosity was predicted and demonstrated in the late 1940 s [29]. This type of correlation has been found to hold for a large number of simple fluid foods including molten hard candies, concentrated coffee and concentrated milk. Shown in Figure 4.7.6 are the relaxation times measured at 10 MHz for solutions of rehydrated instant coffee compared with measured Newtonian viscosities of the solution. The correlations and the measurement provide an accurate estimate of viscosity at a specific shear rate. 

The general equation of convective diffusion in liquids, equation (15), is a second-order, partial differential equation with variable coefficients. Its solution yields the spatial distribution of c, as a function of time, namely its transient behaviour. On an analytical level, solution of equation (15) into the transient c(t) is possible only for a number of relatively simple systems with well-defined geometry and flow properties. The problem is greatly simplified if the concentration function Cj(x,y,z) is essentially independent of time t, i.e. in the steady-state. Then equation (15) reduces to ... 

In turbulent flow, properties such as the pressure and velocity fluctuate rapidly at each location, as do the temperature and solute concentration in flows with heat and mass transfer. By tracking patches of dye distributed across the diameter of the tube, it is possible to demonstrate that the liquid s velocity (the time-averaged value in the case of turbulent flow) varies across the diameter of the tube. In both laminar and turbulent flow the velocity is zero at the wall and has a maximum value at the centre-line. For laminar flow the velocity profile is a parabola but for turbulent flow the profile is much flatter over most of the diameter. 

Compared to dilute solution viscometry and to some extent to bulk rheology, the flow properties of dendrimers in concentrated solutions have been the least investigated area of dendrimer rheology. In fact, with the notable exception of some recent data on generation 4 PPI in water [22] the only [32] reported... 

Solution viscosity measurements for Mn are calibrated from the flow characteristics of linear molecules of the equilibrium molecular weight distribution. Branched polymers have a lower radius of gyration for their molar mass than the corresponding linear molecule. One, therefore, expects different flow properties as branching increases, hence causing the viscosity numbers to become less and less accurate and so should only be used for trends - not exact calculations. 

Mayrath, J.E., "A Flow Microenthalpimetric Survey of Electrolyte Solution Thermodynamic Properties from 373K to 473K"... 

Also included are sections on how to analyze mechanisms that affect flux feature models for prediction of micro- and ultrafiltration flux that help you minimize flux decline. Descriptions of cross-flow membrane filtration and common operating configurations clarify tf e influence of important operating parameters on system performance. Parameters irdlucnc irxj solute retention properties during ultrafiltration arc identified and discussed or treated in detail. 

To prepare croscarmellose sodium, crude cellulose is steeped in sodium hydroxide solution [1] and treated with sodium monochloroacetate to form carboxymethylcellu-lose sodium. After completion of the reaction, the excess sodium monochloroacetate slowly hydrolyzes to glycolic acid. The glycolic acid converts a few of the sodium earboxymethyl groups to the free acid and catalyzes the cross-linkage to form croscarmellose sodium. The by-products sodium chloride and sodium glycolate can be removed by extraction with alcohol to achieve 99.5% purity. Croscarmellose sodium may be milled to break the polymer fibers into shorter lengths and hence improve flow properties. 

Ciystallization from solution is an important separation and purification process in a wide variety of industries. These range from basic materials such as sucrose, sodium chloride and fertilizer chemicals to pharmaceuticals, catalysts and specialty chemicals. The major purpose of crystallization processes is the production of a pure product. In practice however, a number of additional product specifications are often made. They may include such properties as the ciystd size distribution (or average size), bulk density, filterability, slurry viscosity, and dry solids flow properties. These properties depend on the crystal size distribution and crystal shape. The goal of crystallization research therefore, is to develop theories and techniques to allow control of purity, size distribution and shape of crystals. 

Industrially, HECs with DS values below 2 are used. Low DS materials (to about 0.5) are soluble only in basic solutions while those with DS values of about 1.5 are water soluble. Concentrated solutions of HEC are pseudoplastic with their apparent viscosities decreasing with increased rates of shear. Dilute solutions approach being Newtonian in their flow properties, even under a wide range of shear rates. 

While Eq. (10) is mathematically similar to Eq. (9), it is dramatically different when H is significantly different from unity. It is evident from Eqs. (9) and (10) that k em does depend on the diffusion coefficient of the solute in the solvent within the pores and effective thickness, S, which is a membrane property. It does not depend on flow properties of the adjacent solutions. The flow properties affect only and kout-... 

Given the vast number of possible matrix-reinforcement combinations in composites and the relative inability of current theories to describe the viscosity of even the most compositionally simple suspensions and solutions, it is fruitless to attempt to describe the momentum transport properties of composite precursors in a general manner. There are, however, two topics that can be addressed here in an introductory fashion flow properties of matrix/reinforcement mixtures and flow of matrix precursor materials through the reinforcement. In both cases, we will concentrate on the flow of molten polymeric materials or precursors, since the vast majority of high-performance composites are polymer-based. Fnrthermore, the principles here are general, and they apply to the flnid-based processing of most metal-, ceramic-, and polymer-matrix composites. 

It appears that one can develop a qualitative understanding of the simple flow properties at moderate concentration without going beyond concepts which are already inherent either in the dilute solution theory of polymers or in the properties of particulate suspensions. The dependence of viscosity on c[i ] is believed to reflect a particle-like or equivalent sphere (127) hydrodynamics in solutions of low to moderate concentration. In particular, the experimental facts do not force the consideration of effects which might arise from the permanent connectedness of the polymer backbones. Situations conducive to the entangling of molecules may be present, e.g., overlap of the coils, but either entanglement contributions are small, or else they are overwhelmed by the c[f ] interactions. 

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