Simple colloids

In simple colloids, a clear distinction can be made between the disperse phase and the disperse medium, for example, simple emulsions of... 

The particles in a colloidal dispersion are sufficiently large for definite surfaces of separation to exist between the particles and the medium in which they are dispersed. Simple colloidal dispersions are, therefore, two-phase systems. The phases are distinguished by the terms dispersed phase (for the phase forming the particles) and dispersion medium (for the medium in which the particles are distributed) - see Table 1.1. The physical nature of a dispersion depends, of course, on the respective roles of the constituent phases for example, an oil-in-water (O/W) emulsion and a water-in-oil (W/O) emulsion could have almost the same overall composition, but their physical properties would be notably different (see Chapter 10). 

Simple colloidal dispersions are two-phase systems, comprising a dispersed phase of small particles, droplets or bubbles, and a dispersion medium (or dispersing phase) surrounding them. Although the classical definition of colloidal species (droplets, bubbles, or particles) specifies sizes of between one nanometre and one micrometre, in dealing with practical applications the upper size limit is frequently extended to tens or even hundreds of micrometres. For example, the principles of colloid science can be usefully applied to emulsions whose droplets exceed the 1 tm size limit by several orders of magnitude. At the other extreme, the field of nano-... 

The key link between ELS experiments and particle electrostatic properties is the theoretical model of colloidal electrohydrodynamics. The required model is considerably more complicated than the one needed in the interpretation of DLS data. DLS relies upon a relatively simple colloidal hydrodynamic model to relate the measured particle diffusivity to particle radius via the Stokes-Einstein Eq. (39). The colloidal electrohydrodynamic model for ELS must account for the complex physical/chemical/electrical structure of the particle surface as well as the distortion of the diffuse part of the electrostatic double layer due to the motion of the particle through the medium. 

Czekelius C., Hilgendorff M., Spanhel L., Bedja 1., Lerch M., Muller G., Bloeck U., Su D. S. and Giersig M. (1999), A simple colloidal route to nanocrystalline ZnO/CulnSi bilayers . Advanced Materials 11, 643-646. 

In the above examples, which may be called simple colloids, a clear distinction can be made between the disperse phase and the dispersion medium. However, in network colloids this is hardly possible since both phases consist of interpenetrating networks, the elements of each being of colloidal dimensions. Porous solids, in which gas and solid networks interpenetrate, two-phase glasses (opal glasses), and many gels are examples of this category. 

Some of the more important types of colloidal systems outlined above are summarised in Table 1.1. For simplicity we shall limit ourselves in this book to a discussion of simple colloids, although the ideas developed can be extended and applied to more complex systems. 

The thyroid gland possesses a proteolytic enzyme this was first demonstrated by De Robertis (1941) in follicular colloid extracted from single follicles of rats thyroids the proteolytic activity of the enzyme was increased after the administration of thyrotropin and was decreased after administration of iodide. The activity of the enzyme was shown (De Robertis and Nowinski, 1946) to vary in different pathological conditions in human beings in cases of severe toxic goiter it was increased to twice the normal activity in simple colloid goiter it was appreciably lowered. 

The DLVO theory assumes that there are two forces at play in simple colloidal systems which balance each other in such a way as to kinetically stabilize the suspension. It is important to emphasize that the true equilibrium state of nearly all colloidal systems is the fully aggregated one, i.e. given enough time, colloidal systems will ultimately collapse. The DLVO theory captures both features, and this is the key to its appeal. The balance of repulsive electrostatic and attractive dispersion forces produces a kinetic barrier to full aggregation often, stable colloidal systems are in effect in a state of suspended animation before ultimate collapse. 

The examples of colloids listed in Table 10.2 may be considered simple colloids because they involve one fairly distinct type of dispersed and continuous phase. In practice, many colloidal systems are much more complex in that they contain a variety of colloidal types, such as a sol, an emulsion (or multiple emulsions), an association colloid, macromolecular species, plus the continuous phase. Such systems are often referred to as complex or multiple colloids. As we shall see, even the simplest colloids can be quite complex in their characteristics. It should be easy to understand, then, why the difficulty of understanding a multiple colloid increases dramatically with the number of components present. 

We can also identify entropy along an individual trajectory. For a simple colloidal particle, the entropy has two contributions. First is an increase in entropy of the medium due to the heat dissipated into the... 

Not only can the i>eptisation of simple colloidal oxides, sulfides, etc., be explained by the above theory, but also that of colloidal mixtures or Kolloidverbindtmgen. The purple of Cassius has been chosen as a representative of this class. Here the purely chemical theoiy. 

Many colloids are two-phase dispersions. Systems where a dispersed phase is distributed within a continuous dispersion medium are called simple colloids or colloidal dispersions. Table 3.1 lists examples of various types of... 

Zeta potential measurements are typically in the millivolt range, and a colloidal suspension with a zeta potential of less than 30 mV is usually considered stable, that is, the suspension will not aggregate spontaneously over a reasonable timescale. Of course, there are complications to this simple colloidal picture. Particles with complex charge distributions such as proteins or with an interesting surface topology (i.e., polymer brushes) may exhibit very different behavior compared to the ideal hard spherical colloid considered in this section. In these cases, a more detailed model for Henry s function is required. 

Churukian, C. J. Rubio, A. Fapham, F. W. A simple colloidal silver method (autometallographic technique) for demons-trating inorganic mercury in hrain sections. J. Histotechnol. 2000, 23, 337-339. 

The present chapter is aimed at reviewing the development and the specific applications of the SCGLE theory of colloid dynamics and of dynamic arrest. Thus, it is not aimed at reviewing the state-of-the-art in either of these research areas, for which excellent reviews are available [2,3,43-45]. We must also say that notable topics in both fields are barely or never mentioned here. This includes, for example, the structural, mechanical, and rheological properties, and the effects of hydrodynamic interactions. Instead, we focus on the treatment of the effects of direct conservative interactions in simple colloidal systems. Thus, here we shall primarily deal with monodisperse suspensions of spherical particles in the absence of hydrodynamic interactions, although the extension to multi-component systems will also be an important aspect of this review. 

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