Rheology contributions

Many properties of colloidal suspensions, such as their stability, rheology, and phase behaviour, are closely related to the interactions between the suspended particles. The background of the most important contributing factors to these interactions is discussed in this section. 

Fats contribute to the rheological properties in flowable and pastry foods. By combining with starches to form a clathrate, a product different from the native starch is formed, eg, shortening in baked goods. The highly developed shortness of pies baked in eadier times resulted from the use of high levels of lard. The use of less fat in pie cmsts is evident, ie, the cmsts are harder and readily become soggy. 

Filler particle si2e distribution (psd) and shape affect rheology and loading limits of filled compositions and generally are the primary selection criteria. On a theoretical level the influence of particle si2e is understood by contribution to the total energy of a system (2) which can be expressed on a unit volume basis as ... 

Rheology. Flow properties of latices are important during processing and in many latex appHcations such as dipped goods, paint, inks (qv), and fabric coatings. For dilute, nonionic latices, the relative latex viscosity is a power—law expansion of the particle volume fraction. The terms in the expansion account for flow around the particles and particle—particle interactions. For ionic latices, electrostatic contributions to the flow around the diffuse double layer and enhanced particle—particle interactions must be considered (92). A relative viscosity relationship for concentrated latices was first presented in 1972 (93). A review of empirical relative viscosity models is available (92). In practice, latex viscosity measurements are carried out with rotational viscometers (see Rpleologicalmeasurement). 

Inks. Refined kaolin is a common ingredient in a large variety of printing inks (qv). In addition to extending the more expensive polymers present, ka olin also contributes to improved color strength, limits the penetration of the ink into the paper, controls rheology, and improves adhesion. Kaolin for this appHcation must usually be as white as possible and free from oversize particles. Surface treated clays are used to improve compatibiHty with oil-based ink. Clays can also be an ingredient in the newer water-based or uv-cured inks. 

The net effect is that tackifiers raise the 7g of the blend, but because they are very low molecular weight, their only contribution to the modulus is to dilute the elastic network, thereby reducing the modulus. It is worth noting that if the rheological modifier had a 7g less than the elastomer (as for example, an added compatible oil), the blend would be plasticized, i.e. while the modulus would be reduced due to network dilution, the T also would be reduced and a PSA would not result. This general effect of tackification of an elastomer is shown in the modulus-temperature plot in Fig. 4, after the manner of Class and Chu. Chu [10] points out that the first step in formulating a PSA would be to use Eqs. 1 and 2 to formulate to a 7g/modulus window that approximates the desired PSA characteristics. Windows of 7g/modulus for a variety of PSA applications have been put forward by Carper [35]. 

Acrylamide polymers are used as multipurpose additives in the oil-producing industry. Introduction of polymers into drilling fluids-drilling muds improves the rheological properties of the fluids in question, positively affects the size of suspended particles, and adds to filterability of well preparation to operation. Another important function is soil structure formation, which imparts additional strength to the well walls. A positive effect is also observed in secondary oil production, where acrylamide polymers additives improve the mobility of aqueous brines injections, which contribute to... 

Sources of Toxicity. There are three contributing mechanisms of toxicity in drilling fluids, chemistry of mud mixing and treatment, storage/disposal practices, and drilled rock. The first group conventionally has been known the best because it includes products deliberately added to the system to build and maintain the rheology and stability of drilling fluids. 

An understanding of the contribution of the relevant physical and chemical properties of the system to rheological behaviour is an area which has made little progress until recent... 

SFA has made a great contribution to the investigations of thin him rheology [41], The measurements on SFA conhrm that there is a signihcant enhancement of the effective viscosity in molecularly thin liquid hlms, and the viscosity grows constantly as the him thickness diminishes. 

The interfacial rheologic properties are extremely sensitive parameters toward the chemical composition of immiscible formation liquids [1053]. Therefore comparison and interpretation of the interfacial rheologic properties may contribute significantly to extension of the spectrum of the reservoir characterization, better understanding of the displacement mechanism, development of more profitable enhanced and improved oil-recovery methods, intensification of the surface technologies, optimization of the pipe line transportation, and improvement of the refinery operations [1056]. 

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,... 

Both of these models show contributions from the viscosity and the elasticity, and so both these models show viscoelastic behaviour. You can visualise a more complex combination of models possessing more complex constitutive equations and thus able to describe more complex rheological profiles. 

The major difficulty in predicting the viscosity of these systems is due to the interplay between hydrodynamics, the colloid pair interaction energy and the particle microstructure. Whilst predictions for atomic fluids exist for the contribution of the microstructural properties of the system to the rheology, they obviously will not take account of the role of the solvent medium in colloidal systems. Many of these models depend upon the notion that the applied shear field distorts the local microstructure. The mathematical consequence of this is that they rely on the rate of change of the pair distribution function with distance over longer length scales than is the case for the shear modulus. Thus... 

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