Disperse systems matter

The spontaneous direction of any process is toward greater dispersal of matter plus energy. If we are to apply this criterion in a quantitative way, we need ways to measure amounts of dispersal. Scientists analyze the constraints on a system to measure the dispersal of matter. The more the system is constrained, the less dispersed it is. Scientists do calculations on the flow of heat to measure changes in the dispersal of energy. 

AS > 0 since the system is becoming more disordered, i.e. the sugar molecules disperse throughout the tea., allowing the sugar molecules and the aqueous tea solution to transfer energy to each other. Dispersal of matter allows for more dispersal of energy. 

An emulsion is a dispersed system of two immiscible phases. Emulsions are present in several food systems. In general, the disperse phase in an emulsion is normally in globules 0.1-10 microns in diameter. Emulsions are commonly classed as either oil in water (O/W) or water in oil (W/O). In sugar confectionery, O/W emulsions are most usually encountered, or perhaps more accurately, oil in sugar syrup. One of the most important properties of an emulsion is its stability, normally referred to as its emulsion stability. Emulsions normally break by one of three processes creaming (or sedimentation), flocculation or droplet coalescence. Creaming and sedimentation originate in density differences between the two phases. Emulsions often break by a mixture of the processes. The time it takes for an emulsion to break can vary from seconds to years. Emulsions are not normally inherently stable since they are not a thermodynamic state of matter. A stable emulsion normally needs some material to make the emulsion stable. Food law complicates this issue since various substances are listed as emulsifiers and stabilisers. Unfortunately, some natural substances that are extremely effective as emulsifiers in practice are not emulsifiers in law. An examination of those materials that do stabilise emulsions allows them to be classified as follows ... 

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. 

Foam is a disperse system with a high surface area, and consequently foams tend to collapse spontaneously. Ordinarily, three-dimensional foams of surfactant solutes persist for a matter of hours in closed vessels. Gas slowly diffuses from the small bubbles to the large ones (since the pressure and hence thermodynamic activity of the gas within the bubbles is inversely proportional to bubble radius). Diffusion of gas leads to a rearrangement of the foam stmctures and this is often sufficient to rupture the thin lamellae in a well-drained film. 

Disperse systems consist normally of two or more phases in which the continuous phases are intermixed. If, in a continuous phase (the dispersion medium), the elements of the disperse matter are embedded such that they can be individually distinguished, the system is called discretely disperse, A coherent disperse phase, which may also consist of well-defined elements adhering to or intermixed with each other, is called compact disperse. 

In addition to these four typical binding mechanisms (Figure 14a to d), whereby bonding occurs at the coordination points, three other models exist. Form-closed bonds (e) are only possible if the particulate matter is shaped such that, somehow, it can interlock and capillary forces (f) can only become effective in a disperse system which is filled with a liquid that forms concave menisci at the pore ends. In the third case, particles forming the agglomerate are embedded in a matrix of binder the model can also be depicted by Figure 14(f) where the dark areas represent the binder matrix. 

In disperse systems where coagulation and coalescence occur with very low rates, and under the conditions of substantial solubility of dispersed matter, the decrease in degree of dispersion may be caused by the matter transfer from smaller particles to the larger ones. These processes are quite common in nature and may take place in a variety of disperse systems, such as lyosols, suspensions, emulsions, foams, aerosols, in the systems with solid... 

This Chapter describes preparation, structure, and properties of different colloidal systems. A lot of attention will be devoted to the connection between particular properties of disperse systems (and possible ways that can be used to monitor colloid stability) and the aggregate states of both the dispersed matter and dispersion medium. 

Disperse systems with gaseous dispersion medium, regardless of the aggregate state of dispersed phase, are referred to as aerosols. The systems in which the dispersed phase is liquid are referred to as fogs those in which it is solid are called smokes in the case of finely dispersed matter or dusts and powders in the case of coarsely dispersed matter. Aerosols in which the liquid phase is present due to vapor condensation at the surface of solid particles along with the solid phase, are commonly referred as smogs . Aerosols of this type are usually present in the atmosphere of large industrialized cities. 

This book covers major areas of modern Colloid and Surface Science (in some countries also referred to as Colloid Chemistry) which is a broad area at the intersection of Chemistry, Physics, Biology and Material Science investigating the disperse state of matter and surface phenomena in disperse systems. The book arises of and summarizes the progress made at the Colloid Chemistry Division of the Chemistry Department of Lomonosov Moscow State University (MSU) over many years of scientific, pedagogical and methodological work. 

In liquid/fluid disperse systems (emulsions, foams for example) the liquid interface is usually covered by an adsorption layer and often imder lateral movement. This movement causes lateral transport along the interface and brings the adsorption layer out of its equilibrium state so that an adsorption/desorption exchange of matter sets in. 

Although emulsion stability is not a concept with a well-agreed-on definition, it is always linked either to the persistence or to the decay of the dispersed system under certain circumstances. As a matter of fact, it is a fundamental emulsion property and a lot of attention has been dedicated to its study (10,11). 

The behavior of emulsions as a particular type of disperse system is controlled by many factors. There is a large number of properties of the corresponding liquid/ liquid interface which can be determined by well-established methods, such as dynamic surface tensions, adsorbed amount, exchange of matter across the interface, and dilational and shear rheology. Although first models exist, a general view... 

A new idea, using deterministic approach, has been applied for the elucidation of the electron and momentum transfer phenomena at both the rigid and deformable interfaces in finely (micro, nano, atto) dispersed systems. Since the events at the interfaces of finely dispersed systems have to be considered at the molecular, atomic, and entities level, it is inevitable to introduce the electron transfer besides the classical heat, mass, and momenrnm transfers commonly used in chemical engineering [8]. Therefore, an entity can be defined as the smallest indivisible element of matter that is related to the particular transfer phenomenon. Hence, the entity can be either a differential element of mass or demon, or an ion, or a phonon as quantum of acoustic energy, or an infon as quantum of information, or a photon, or an electron [9,10]. 

Because the lower limit of the colloidal range is just larger than the size of some molecules and solvated species it is difficult to determine exactly where the distinction between surface and bulk ends and a molecularly dispersed system begins. For macromolecular systems, of course, the molecular size is such that even a molecular dispersion or solution easily falls into the size range of colloids. For that reason, primarily, such systems are referred to as lyophilic colloids, even though the properties of such systems are governed for the most part by phenomena distinct from the classic surface interactions considered in lyophobic colloids. It is no trivial matter, therefore, to decide just where surface effects end and the characteristics of the individual free, solvated units begin. 

In general, stability means the quality of a substance or a system to remain at the same state. In practice, one needs to specify if state refers to the isotopes of elements, the chemical composition, the state of matter, or something else. When talking about the stability of colloidal suspensions or suspension stability, one usually addresses the size distribution of the particles, the homogeneity of the disperse system, and/or the stmcture of the suspension. Hence, the meaning of suspension stability is somewhat ambiguous. Moreover, a suspension can be... 

Dispersion (STATE OE MATTER) generic term for dispersed systems with a fluid continuum. 

The context of heterogeneity and dispersity requires that the material forming the dispersed phase is insoluble/immiscible in the continuous phase. From that follows directly that the interfaces in dispersed systems can be made of all possible combinations of states of matter except the gas-gas combination. Examples of dispersed colloidal systems are given in Table 1. It is interesting to note that indeed all of these combinations can be used to carry out polymerizations. The various kinds of heterophase polymerization techniques are put together in Table 2 in the order of ascending number of components the components are hsted, except the initiating system. 

Understand the relationship of entropy to the dispersal of energy and dispersal of matter (disorder) in a system Use tabulated values of absolute entropies to calculate the entropy change, AS ... 

---