Colloidal system physical stability

The various flocculation models which are valid in the different regimes described above allow one to compute the particle/ particle collision rate for any given particle sizes, chemical and physical condition. From the magnitude of this collision rate, one can estimate a colloidal system s stability in cases (iv) and (v). However, in cases (ii) and (iii), both flocculation and creaming will be important in the colloidal breaking process. Consequently, in order to determine whether a colloidal system will be stable in these two cases, we have to determine the net rate of particle loss due to both creaming and flocculation. 

As we introduced in the preceding section, colloidal systems are stabilized by a delicate balance of competing forces. These forces either act to repel the colloidal particles from each other or mutually attract them into aggregates. Colloidal particles are small, and as a result a colloidal system can have an extremely high surface area-to-volume ratio. Consider a 1-cm cube of gold the surface area-to-volume ratio of the cube is 6 cm /l cm. Now, if we take that same cube of gold but split it into 10-nm wide cubes, the total surface area-to-volume increases to 6 X 10 cm /1 cm. This calculation shows that as particle size decreases, the surface interactions between particles increase in importance and tend to dominate the physics of the system at very small particle sizes. 

Sengupta S and Sood AK. 1991. Theory of liquid-bcc-fcc coexistence in charge-stabilized colloidal systems. Physical Review A 44 1233-1236. 

The use of hydrophylic colloids, vegetable gums, stabilizers—call them what you will—falls in this category. The achievement of a texture, a feel, an appearance, a unique physical system, are trade advantages worth holding. 

A. Impact of Physical Interactions between Biopolymers on Structure and Stability of Colloidal Systems... 

The forces acting between two surfaces in contact or near - contact determine the behavior of a wide spectrum of physical properties. These can include friction, lubrication, the flow properties of particulate dispersions, and, in particular, the adsorption and adhesion phenomena, the stability of colloidal system [1,2] and the ability to form Langmuir monolayer at the air - water interface. 

Physical Stability of Drug Suspension. The physical stability of the non-polar drug suspensions formulated in pMDIs again depends on many parameters, such as propellant type, chemical properties of the drug compounds, and the surfactants used in the formulation. A suspension is a liquid system in which insoluble solid particles are dispersed in a liquid medium. Suspensions can be divided into colloidal suspensions, in which the... 

The physical stability of a colloidal system is determined by the balance between the repulsive and attractive forces which is described quantitatively by the Deryaguin-Landau-Verwey-Overbeek (DLVO) theory. The electrostatic repulsive force is dependent on the degree of double-layer overlap and the attractive force is provided by the van der Waals interaction the magnitude of both are a function of the separation between the particles. It has long been realized that the zeta potential is a good indicator of the magnitude of the repulsive interaction between colloidal particles. Measurement of zeta potential has therefore been commonly used to assess the stability of colloidal systems. 

Most of the ensuing part of this book deals with dispersed systems. These generally have one or more kinds of interface, often making up a considerable surface area. This means that surface phenomena are of paramount importance, and they are discussed in Chapter 10. Colloidal interaction forces between structural elements are also essential, as they determine rheological properties and physical stability these forces are the subject of Chapter 12. The various kinds of physical instability are treated in Chapter 13, and the nucleation phenomena involved in phase transitions in Chapter 14. Specific dispersed systems are discussed in Chapters 11 and 17. The present chapter explains important concepts and discusses geometrical aspects. 

Professor Shchukin also performed general editing of the manuscript utilizing his experience in lecturing this course and paying special attention to the presentation of the concepts and applications of physical-chemical mechanics of disperse systems and materials, properties of the structure-rheological barrier as a factor of strong stabilization, some features of lyophilic colloidal systems and other research areas, explored by Russian scientific schools and less known abroad. 

From a theoretical point of view, adsorption at interfaces, either solid-liquid (S/L). liquid-vapor (L/V>, or liquid-liquid (L/L), is one of the topic.s of highest interest in the physical chemistry of colloidal systems due to the increasing number of important technological areas in which it finds application. We will only be here concerned with solid-liquid interfaces and. in particular, with the two main ways of favoring stabilization of pharmaceutical suspensions, which are the adsorption of surfactants and of polymers as additives in suspension. Let us first consider the fundamentals of these processes and later some results will be discussed. 

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) ... 

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