Colloids size range

Although the remainder of this contribution will discuss suspensions only, much of the theory and experimental approaches are applicable to emulsions as well (see [2] for a review). Some other colloidal systems are treated elsewhere in this volume. Polymer solutions are an important class—see section C2.1. For surfactant micelles, see section C2.3. The special properties of certain particles at the lower end of the colloidal size range are discussed in section C2.17. 

The vibratoiy-tube mill is also suited to wet milhng. In fine wet milling this narrow residence time distribution lends itself to a simple open circuit with a small throughput. But for tasks of grinding to colloid-size range, the stirred media mill has the advantage. 

Another classification scheme is based on the size of the dispersed particles within the dispersion medium (Table 2). The particles of the dispersed phase may vary considerably in size, from large particles visible to the naked eye, down to particles in the colloidal size range, and particles of atomic... 

A colloid is defined as a system consisting of discrete particles in the size range of 1 nm to 1 pm, distributed within a continuous phase [153], On the basis of the interaction of particles, molecules, or ions of the disperse phase with molecules of the dispersion medium-, colloidal systems can be classified as being lyophilic or lyophobic. In lyophilic systems, the disperse phase molecules are dissolved within the continuous phase and in the colloidal size range or spontaneously form aggregates in the colloidal size range (association systems). In lyophobic systems, the disperse phase is very poorly soluble or insoluble in the continuous phase. During the last several decades, the use of colloids in... 

Analytical-operational Difficulties. In order to work close to the conditions in natural waters, very low concentrations of metal ions (in the nanomolar range) and of particles as well as pH values in the neutral range have to be used. Analytical difficulties occur because of undesired adsorption of metal ions to the experimental devices (walls of beakers, glass filtration devices, etc.) and of insufficient separation of the particulate and dissolved phase (particles in the colloidal size range). 

There are many situations in which polymer networks contain a filler. The particle size is frequently chosen to be in the colloidal size range. 

Some marine chemists define the upper end of the colloid size range as either 10 pm (Figure 3.2) or 0.1 xm (Figure 5 3)... 

Material comprising more than one phase where at least one of the phases consists of finely divided phase domains, often in the colloidal size range, distributed throughout a continuous phase domain. 

Note 2 Particles in the colloidal size range have linear dimensions [3] between 1 run and 1 xm. 

Particle size is one of the most important characterization parameters for sohd hpid nanoparticle dispersions, and parameters relahng to particle size are consequently reported in all stndies on these systems. Particle size determinations are predominantly performed to conhrm that the desired colloidal size range has been obtained dnring preparation and that it is retained upon storage or further processing (e.g., during freeze drying or sterilization). 

In subsequent sections of this chapter, we discuss further the distinction between macromolec-ular colloids and multiphase dispersions (Section 1.3), the use of the term stability in colloid science (Section 1.4), the size and shape of colloidal particles, the states of aggregation among particles, and the distribution of particle sizes that is typical of virtually all colloidal preparations (Section 1.5). The fact that particles in the colloidal size range are not all identical in size also requires a preliminary discussion of statistics, which is the subject of Section 1.5c and Appendix C. 

The contemporary science student is probably aware that the concept of the atom is traceable to early Greek philosophers, notably Democritus. More than likely, however, few have bothered to follow through the hypothetical subdivision process that led to the original concept of an atom. The time has come to remedy this situation since, as mentioned above, the colloidal size range lies between microscopic chunks of material and individual atoms. 

Above we used the words continuous phase and dispersed phase to refer to the medium and to the particles, respectively, in the colloidal size range. It should be understood that these are solvent and solute in lyophilic systems. In micellar systems, the micelles are dispersed in an aqueous continuous phase. Furthermore, the system as a whole is generally called a dispersion when we wish to emphasize the colloidal nature of the dispersed particles. This terminology is by no means universal. Lyophilic dispersions are true solutions and may be called such, although this term ignores the colloidal size of the solute molecules. 

The equilibrium between gravitational or centrifugal force and diffusion is routinely taken advantage of in colloid science, as illustrated in Vignette II. Our objective in this chapter is to examine the effects of sedimentation and diffusion, first taken separately and then combined, on particles in the colloidal size range. 

Until now, we have been primarily concerned with the definition and measurement of viscosity without regard to the nature of the system under consideration. Next we turn our attention to systems containing dispersed particles with dimensions in the colloidal size range. Viscosity measurements can be used to characterize both lyophobic and lyophilic systems we discuss both in the order cited. 

Since Rayleigh scattering does not apply to particles in the colloidal size range, we do not present the derivation in detail instead, Table 5.1 summarizes some key steps in the development of the Rayleigh equation ... 

For example, Equation (39) suggests that light scattering is a technique ideally suited to the study of particles in the colloidal size range since the turbidity increases with the molecular... 

Above a certain concentration, the turbidity of sodium dodecyl sulfate (molecular weight = 288) solutions increases with concentration as if particles in the colloidal size range were present. Use the following dataf to evaluate the apparent molecular weight of the species responsible for the scattering. For this system H = 3.99 x 10 6. 

Suppose your employer intends to develop a new laboratory to characterize particles in the colloidal size range. Your assignment is to prepare a list of the equipment that should be purchased for such a facility. A brief justification for each major item should be included along with a priority ranking based on the versatility of the method. Assume that your laboratory is already well stocked with such nonspecialized items as laboratory glassware, balances, and the like. 

The average particle size is at the upper end of the colloidal size range (on the order of micrometers), and the particles are usually visible in a light microscope. We shall describe these as coarse emulsions when we want to emphasize their size range. Because the particles are relatively large and polydisperse, coarse emulsions look white when examined visually. 

The interaction between individual molecules obviously plays an important role in determining, for example, the nonideality of gas, as illustrated in Example 10.2. It is less clear how to apply this insight to dispersed particles in the colloidal size range. If atomic interactions are assumed to be additive, however, then the extension to macroscopic particles is not particularly difficult. Moreover, when dealing with objects larger than atomic dimensions, we also... 

The success and relative simplicity of conductivity as a method of study for small ions prompt us to extend these ideas to particles in the colloidal size range. For the purpose of our discussion here, we can treat a charged colloidal particle as an ion of large charge, hence the name macroion. However, we identify shortly some of the differences between such macroions and small ions with respect to their response to an applied electric field. For certain colloids the experimental aspects of studying mobilities are simpler than for small ions because of the... 

A dispersion of gas bubbles in a liquid, in which at least one dimension falls within the colloidal size range. Thus a foam typically contains either very small bubble sizes or, more commonly, quite large gas bubbles separated by thin liquid films. The thin liquid films are called lamellae (or laminae ). Sometimes distinctions are drawn as follows. Concentrated foams, in which liquid films are thinner than the bubble sizes and the gas bubbles are polyhedral, are termed polyederschaum . Low-concentration foams, in which the liquid films have thicknesses on the same scale or larger than the bubble sizes and the bubbles are approximately spherical, are termed gas emulsions , gas dispersions , or kugelschaum . See also Evanescent Foam, Froth, Aerated Emulsion. 

Colloids are systems with size intermediate between the microscopic and macroscopic realms. They have been defined as particles with a characteristic dimension between a micron and a few nanometers or, alternatively, as entities containing between 103 and 109 atoms. With their small size, colloids have a very large surface-to-volume ratio and surface interactions are dominant in determining their stability. Some properties of systems in the colloidal size range are as follows ... 

Figure 9.9. Separation of polystyrene latex beads of indicated diameters in the colloidal size range by SdFFF programmed from 1500 to 75rpm at 2mL/min flowrate. (Courtesy of Bhajendra N. Barman, FFFractionation. Inc.)...

Particles within the colloidal size range can also be made by breaking down massive gold by the input of the necessary energy.16 When this is mechanical, the process is termed attrition, but more useful is metal vapour synthesis... 

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