Colloidal systems characteristic properties

In Chapter 17, we discuss rheological properties, in particular viscosity and elasticity, of colloidal systems. These properties are at the basis of quality characteristics such as strength, pliancy, fluidity, texture, and other mechanical properties of various materials and products. In addition to bulk rheology, rheological features of interfaces are discussed. Interfacial rheological behavior is crucial for the existence of deformable dispersed particles in emulsions and foams. Emulsions and foams, notably their formation and stabilization, are considered in more detail in Chapter 18. 

We have found that in the system of presulfate initiator, the PVAc latexes are not dissolved transparently in the methanol-water mixture [8], and in the system of HPO initiator, the extraction of the polymer from the PVAc latex films with acetone greatly depends on the polymerization condition [9]. These results suggest that if a polymerization method can be found in which the grafting polymerization of VAc onto PVA is controlled to the minimum, a large portion of PVAc in the latex film will have a chance of extraction with solvents. In this Chapter, the preparations of the unique porous films from the PVAc latexes containing PVA as a protective colloid by an extraction of the PVAc particles with acetone and the characteristic properties of the porous films are summarized. 

In the past few decades, a specific kind of colloidal system based on monodis-perse size has been developed for various industrial applications. A variety of metal oxides and hydroxides and polymer lattices have been produced. Monodisperse systems are obviously preferred since their properties can be easily predicted. On the other hand, polydisperse systems will exhibit varying characteristics, depending on the degree of polydispersity. 

The natural laws of physics and chemistry which describe the behaviour of matter in the massive and molecular states also, of course, apply to the colloidal state. The characteristic feature of colloid science lies in the relative importance which is attached to the various physicochemical properties of the systems being studied. As we shall see, the factors which contribute most to the overall nature of a colloidal system are ... 

As discussed in Chapters 1-7, diffusion, Brownian motion, sedimentation, electrophoresis, osmosis, rheology, mechanics, interfacial energetics, and optical and electrical properties are among the general physical properties and phenomena that are primarily important in colloidal systems [12,13,26,57,58], Chemical reactivity and adsorption often play important, if not dominant, roles. Any physical chemical feature may ultimately govern a specific industrial process and determine final product characteristics, and any colloidal dispersions involved may be deemed either desirable or undesirable based on their unique physical chemical properties. Chapters 9-16 will provide some examples. 

The colloidal state of matter is distinguished by a certain range of particle size, as a consequence of which certain characteristic properties become apparent. Colloidal properties are in general exhibited by substances of particle size ranging between 0 2 /an and 5 nm (2 x 10"7 and 5 x 10"9 m). Ordinary filter paper will retain particles up to a diameter of 10-20/an (1-2 x 10" 5 m), so that colloidal solutions, just like true solutions, pass through an ordinary filter paper (the size of ions is of the order of 0-1 nm = 10 10 m). The limit of vision under the microscope is about 5-10 nm (5-10 x 10 9 m). Colloidal solutions are therefore not true solutions. Close examination shows that they are not homogeneous, but consist of suspension of solid or liquid particles in a liquid. Such a mixture is known as a disperse system the liquid (usually water in qualitative analysis) is called the dispersion medium and the colloid the disperse phase. 

In the colloidal realm, given the large surface-to-volume ratio and the relatively small range of force that can sway the disposition of a colloidal particle, it is easy to appreciate the importance of controlling surface properties. Research literature abounds with the characteristics of colloid systems and model systems that mimic colloid surfaces. Applications permeate the fields of materials processing, adhesion, coatings, food science, and medicine. 

Such a combination of features characteristic of two-phase and one-phase systems allows one to utilize different approaches in investigating colloidal systems. On the one hand, one can treat dispersions as two-phase systems with some peculiar properties, taking into... 

The dynamic electrophoretic mobility is a useful system characteristic. For instance, it provides a means for determining the isoelectric point from electroacoustic measurements. Other properties of colloidal dispersions, namely -potential and particle size, can also be obtained from measurements of dynamic electrophoretic mobility. For a dilute dispersion (less then a few weight percent) of spherical particles, the dynamic electrophoretic mobility is given by a Smoluchowski-type relationship [37,38] ... 

In later chapters we shall discuss the properties of a variety of colloidal systems. However, as a preparation for our consideration of the general properties and stability of dispersions, it will be useful to use one simple example to outline some of their more important characteristics. It so happens that one of the first colloidal dispersions to have been examined systematically will suit our purpose admirably. 

In the colloidal range, the surface volume ratio is extremely high. All properties related to surfaces are therefore accentuated in this range. The limit or boundary between two homogeneous phases, the interface, shows characteristic properties. These properties of the interface, the surface properties, play a predominant role in colloidal systems. This is why it is sometimes said that... 

In connection with the ideas mentioned above it was quite natural thaJ as the guiding principle in experimental work a predilection as to the importance of the colloid component in a poly-component system temporarily prevailed. This component would determine the characteristic properties of the total system, and... 

The limiting case No. 7, does not really belong to Colloid Science because both ions fall below the agreed dimensions nevertheless No. 4, 5, 6 and 7 form a completely allied group. Characteristic properties of 4 are to be found not only in 5 and 6 where at any rate one colloid is present but also in 7 in which there is no longer any colloid at all. The limiting case No. 7 is therefore theoretically important because it shows us clearly that the essentials of the dicomplex colloid systems No. 4, 5 and 6 cannot be sought in the macromolecular structure of the colloid (or the association nature of the kinetic units in the case of the association colloids) but rather in the electrolyte nature of the macromolecule (or associate). 

Various properties of a colloidal systan, such as its stability and rheological and optical characteristics, are directly related to the size of the particles. For many colloidal systems the particles vary in size such systems are called heterodisperse or... 

Bentonite and colloidal aluminium magnesium silicate are of mineral origin and do not exhibit all colloidal characteristics. They exhibit rheological properties such as becoming more fluid under stress but they are not always transparent. The colloidal systems of silicates have thus characteristics transitional to the coarser disperse systems. They hardly dissociate and are generally not split into ions. Therefore they are categorised (Table 23.14) under non-ionic viscosity enhancers, despite the fact that some dissociation occurs. 

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