Multiphase colloidal system

In this Chapter we deviate from the division of the subject matter in this volume (II) of Colloid Science announced in Chapter I, 5, p. 13 according to the kind of phase or state of dispersion of a multiphase colloid system. The possibility of the production of complex colloid systems is not connected with one of these modes of occurrence but with the electrolytic nature of the colloid(s) in question. 

Perram, C.M., Nicolau, C., and Perram, J.W., Interparticle forces in multiphase colloid systems the resurrection of coagulated sauce beamaise. Nature, 270, 572-573, 1977. 

Lipids exist in most foods as multiphased colloidal systems bound by surface-active phospholipids, proteins and emulsifiers. The oxidative stability of food lipids is greatly affected by the partitioning of the lipid substrates, metal initiators and antioxidants, which is complex and depends on the physical properties of the food. We may consider three types of food systems (see Chapter 10) ... 

Paints or surface coatings are complex multiphase colloidal systems that are appUed as a continuous layer to a surface [1], A paint usually contains pigmented materials to distinguish it from clear hlms that are described as lacquers or varnishes. The main purpose of a paint or surface coating is to provide aesthetic appeal as well as to protect the surface. For example, a motor car paint can enhance the appearance of the car body by providing color and gloss and it also protects the car body from corrosion. 

In sections 7.3.1-7.3.4 we have considered only relatively simple dilute emulsions. Many pharmaceutical preparations, lotions or creams are, in fact, complex semisolid or stmc-tured systems which contain excess emulsifier over that required to form a stabilising mono-layer at the oil/water interface. The excess surfactant can interact with other components either at the droplet interface or in the bulk (continuous) phase to produce complex semisolid multiphase systems. Theories derived to explain the stability of dilute colloidal systems cannot be applied directly. In many cases the formation of stable interfacial films at the oil/water interface cannot be considered to play the dominant role in maintaining... 

Processed foods typically exist in the form of a complex, multiphase, multi-component colloidal systems. The key molecules that facilitate the formation and stabilisation of these structures during processing are called emulsifiers. 

A colloidal system represents a multiphase (heterogeneous) system, in which at least one of the phases exists in the form of very small particles typically smaller than 1 pm but still much larger than the molecules. Such particles are related to phenomena like Brownian motion, diffusion, and osmosis. The terms microheterogeneous system and disperse system (dispersion) are more general because they also include bicontinuous systems (in which none of the phases is split into separate particles) and systems containing larger, non-Brownian, particles. The term dispersion is often used as a synonym of colloidal system. 

This new theory of the non-equilibrium thermodynamics of multiphase polymer systems offers a better explanation of the conductivity breakthrough in polymer blends than the percolation theory, and the mesoscopic metal concept explains conductivity on the molecular level better than the exciton model based on semiconductors. It can also be used to explain other complex phenomena, such as the improvement in the impact strength of polymers due to dispersion of rubber particles, the increase in the viscosity of filled systems, or the formation of gels in colloids or microemulsions. It is thus possible to draw valuable conclusions and make forecasts for the industrial application of such systems. 

The high-energy input necessary for preparing multiphase polymer systems or other colloidal systems pushes these systems far from equilibrium at a critical concentration the energy input and the entropy export are so far above their critical values (i.e. they are supercritical) that a self-organisation process occurs in the form of a phase transition. This is the short, summarised main principle on which the new viewpoint [37] is based. 

In recent years other colloid systems—such as microemulsions—have been found to exhibit a wide range of structures [81,82]. We can observe spontaneous phase separation, flocculation and formation of complex bicontinuous structures after the formation of these colloidal systems. It is not possible to form a colloidal system, whether in a polymeric matrix, in water, or in an organic solvent, without a supercritical input of energy, which is provided by turbulent flow conditions during the formation of microemulsions or melt fracture conditions [86] during the formation of colloidal systems in polymers. It seems that a general principle for the behaviour of multiphase systems has been found. 

D. Guest and D. Langevin. Light-scattering study of a multiphase nneroemuisjun system. J, Colloid Inierl. Sci., 112 208-220, 1986. 

Colloidal systems and dispersions are of great importance in many areas of human activity such as oil recovery, coating, food and beverage industry, cosmetics, medicine, pharmacy, environmental protection etc. They represent multi-component and multiphase (heterogeneous) systems, in which at least one of the phases exists in the form of small (Brownian) or large (non-Brownian) particles (Hetsroni 1982, Russel et al. 1989, Hunter 1993). One possible classification of the colloids is with respect to the type of the continuous phase (dispersions with solid continuous phase like metal alloys, rocks, porous materials, etc. will not be consider). 

Colloidal systems and dispersions are of great importance in oil recovery, waist water treatment, coating, food and beverage industry, pharmaceutical industry, medicine, environmental protection etc. Colloidal systems and dispersions are always multi-component and multiphase systems. In these systems at least one dimension is in a range of colloidal forces action colloidal dispersions/emulsions are examples of three dimensional colloidal systems, while thin liquid films are examples of one dimensional colloidal systems. Mostly colloidal systems are stable because their properties are substantially enhanced by the presence of surfactants and or polymers. The distribution and redistribution of the latter molecules is of the crucial importance for colloidal systems. 

The term interfacial oxidation refers to the complex interaction between constituents in multiphase lipid systems in either promoting or inhibiting lipid oxidation. Interfacial oxidation is a surface reaction dependent on the rate of oxygen diffusion and its interactions with unsaturated lipids, metal initiators, radical generators and terminators, all of which are distributed in different compartments of colloidal systems. 

The held of colloid and interface science has no boundary since chemists, physicists, engineers, biologists and mathematicians can all be engaged in the field. For successful applications in industry, multidisciplinary teams are required. Understanding the basic principles of colloid and interface science will enable industry to develop many complex systems in a shorter period of time. Most colloidal systems used in industry are multiphase and complex formulations. They may contain more than one disperse phase, e.g. suspension/emulsion systems (suspoemulsions). 

Numerous colloidal systems can be identified in nature. Many synthetic materials which are produced and processed are also colloidal systems. Such systems are always multiphasic and are mostly comprised of submicron particles or nanometer particles. The macroscopic properties of colloidal systems are governed by the microscopic interactions of its dispersed constituents with each other and with the surrounding dispersing medium. The properties of such particle systems are dominated by interfacial effects rather than volume effects because of their huge internal surface. 

Although occasionally papers appear speaking of the inapplicability of Gibbs phase rule [Li, 1994, 13] or beyond the Gibbs phase rule [Mladek et al, 2007], this invariably means no more than that one of the ceteris paribus conditions Gibbs already mentioned is not fulfilled for example, the phase rule doesn t cover systems in which rigid semi-permeable walls allow the development of pressure differences in the system. Gibbs explicitly allows for the possible presence of other thermodynamic fields. An extended phase rule has been proposed for, inter alia, capillary systems (in which the number and curvature of interfaces/phases play a role), multicomponent multiphase systems for which relative phase sizes are relevant [Van Poolen, 1990], colloid systems (for which, even if in equilibrium, it is not always easy to say how many phases are present), unusual crystalline materials, and more. 

Most food products and food preparations are colloids. They are typically multicomponent and multiphase systems consisting of colloidal species of different kinds, shapes, and sizes and different phases. Ice cream, for example, is a combination of emulsions, foams, particles, and gels since it consists of a frozen aqueous phase containing fat droplets, ice crystals, and very small air pockets (microvoids). Salad dressing, special sauce, and the like are complicated emulsions and may contain small surfactant clusters known as micelles (Chapter 8). The dimensions of the particles in these entities usually cover a rather broad spectrum, ranging from nanometers (typical micellar units) to micrometers (emulsion droplets) or millimeters (foams). Food products may also contain macromolecules (such as proteins) and gels formed from other food particles aggregated by adsorbed protein molecules. The texture (how a food feels to touch or in the mouth) depends on the structure of the food. 

Multiphase Systems Antioxidant activity depends very much on the lipid substrate used for evaluation and the hydrophilic/lipophihc nature of the anti-oxidative compound. Solubility and partition properties of the compound in the medium affect the activity of antioxidants in the bulk hpid systems. As most foods cannot be related to bulk oil systems (e.g., meat, fish, eggs, mayonnaise, salad dressings, etc.), evaluation of antioxidants in multiphase systems is more relevant to their physical and chemical nature. Because of the very same reasons, several studies have found that compounds exhibiting strong activity against oxidation of lipids in bulk systems are often inefficient in colloidal and emulsion systems. 

Micellar catalysis enables water to be employed as a reaction medium, to gain not only an enhancement in the rate of reaction but also improvements in selectivity and sometimes even to allow the catalyst to be recycled in a simple manner (cf. Section 3.1.1.1). A micellar system is a multiphase system in a colloidal dimension and allows the microheterogenization of a catalyst under special conditions [7]. 

Type of flow pattern(s) involved in an adsorptive bubble separation system depends on the type of process used. For example, bubble fractionation involves two-phase (gas-phase and liquid-phase) bubble flow, while solvent sublation involves multiphase bubble flow in their vertical bubble cells. Foam fractionation involves a two-phase bubble flow in the bottom bubble cell, and a two-phase froth flow in the top foam cell. However, all froth flotation processes (i.e., precipitate flotation, ion flotation, molecular flotation, ore flotation, microflotation, adsorption flotation, macroflotation, and adsorbing colloid flotation) involve multiphase bubble flow and multiphase froth flow. 

Marchisio and Fox, Computational Models for Polydisperse Particulate and Multiphase Systems Mewis and Wagner, Colloidal Suspension Rheology... 

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