Rheological characteristics, mixtures

A mixture of sulfonated styrene-maleic anhydride copolymer and polymers prepared from acrylic acid or acrylamide and their derivatives [759] are dispersants for drilling fluids. The rheologic characteristics of aqueous well drilling fluids are enhanced by incorporating into the fluids small amounts of sulfonated styrene-itaconic acid copolymers [761] and an acrylic acid or acrylamide polymer [755]. 

Kaletunc-Gencer, G. and Peleg, M. 1986. Rheological characteristics of selected food gum mixtures in solution. J. Text. Stud. 17 61-70. 

As discussed earlier, LADDs are complex, multicomponent mixtures consisting of both organic and inorganic compounds dispersed in a liquid matrix. Such compositions can exhibit a broad range of rheological characteristics from simple Newtonian to complex pseudoplastic flow. Shown in Figure 9.6 and Figure 9.7 are flow and viscosity profiles of Newtonian and non-Newtonian fluids as a function of applied shear rate. A number of mathematical models have been proposed [76] to describe the flow characteristics of various systems. These equations are called constitutive equations and are used to predict flow behavior in complex systems. 

Another very common industrial mixing process involving immiscible liquids is emulsification. This is frequently encountered in the food and pharmaceutical industries when very small liquid droplets are created in a second liquid phase. In these cases the resulting mixture is often stable and will separate only after long periods of time. Furthermore, the stable onul-sion will usually be relatively viscous and will often exhibit non-Newtonian rheological characteristics. The dynamics of emulsification is also treated in Chapter 14. 

There are a few other materials that need to be covered for this discussion. The first is solder paste. This is a mixture of minute solder beads, flux, and other materials to give it specific rheological characteristics for dispensing and chemical agents for metal surface preparation. For surface-mount applications, it is typically stenciled onto PWB bonding pads, and then the electronic component is placed upon the solder paste deposit. The paste holds the component in place during the reflow process.The second is flux, which, as mentioned previously, is a key component of solder paste. The flux is a heat-activated chemical agent used to clean solder-able surfaces. Both paste and flux will be covered in subsequent sections of this chapter. 

Rheological properties of a binary mixture melt in the first case are those of a viscous liquid and are changed with temperature and composition due to variations in the thermodynamic interaction between melt components, that is, due to changing miscibility. In the second case, there is no strong dependence of rheological properties on the interaction between immiscible components and the properties are determined mainly by the rheological characteristics of the dispersion media and the dispersed (liquid or solid) phase. 

In our case, also considering the rather complicate composition of the mixtures, we do not intend to fully study the rheological characteristics of these materials, but simply to check whether such blends may present melt properties which can prevent processability with usual machinery. Figures 1 and 2 show the viscosity, r, vs. shear rate, y, of homopolymers and their blends, respectively. The addition of PP and PS reduces the viscosity of the blends in the range of... 

Change in the rheology or flow characteristics ofthe cementitious mixture in the fresh state. 

By examining the characteristics one may get some preliminary information on the physical, mechanical, and rheological behavior of the polymeric mixture, which shall be called hereinafter PVC/EPR. 

Surface dilatational rheology is a very sensitive technique to analyze the competitive adsorption/displacement of protein and LMWE emulsifier at the air-water interface (Patino et al., 2003). A common trend is that the surface dilatational modulus increases as the monolayer is compressed and is a maximum at the highest surface pressures, at the collapse point of the mixed film, and as the content of LMWE in the mixture increases. At higher TT, the collapsed protein residues displaced from the interface by LMWE molecules have important influence on the dilatational characteristics of the mixed films. The mechanical properties of the mixed films also demonstrate that, even at the highest tt, the LMWE is unable to displace completely protein molecules from the air-water interface. 

---