Linear colloidal particles

Solutions containing linear colloidal particles, such as DNA segments or tobacco mosaic virus, are systems which may be modeled by interacting cylindrical polyelectrolytes. We may apply the results derived earlier for... 

Several additional instrumental techniques have also been developed for bacterial characterization. Capillary electrophoresis of bacteria, which requires little sample preparation,42 is possible because most bacteria act as colloidal particles in suspension and can be separated by their electrical charge. Capillary electrophoresis provides information that may be useful for identification. Flow cytometry also can be used to identify and separate individual cells in a mixture.11,42 Infrared spectroscopy has been used to characterize bacteria caught on transparent filters.113 Fourier-transform infrared (FTIR) spectroscopy, with linear discriminant analysis and artificial neural networks, has been adapted for identifying foodbome bacteria25,113 and pathogenic bacteria in the blood.5... 

The gel point is defined as the point at which the entire solid mass becomes interconnected. The physical characteristics of the gel network depends upon the size of particles and extent of cross-linking prior to gelation. Acid-catalysis leads to a more polymeric form of gel with linear chains as intermediates. Base-catalysis yields colloidal gels where gelation occurs by cross-linking of the colloidal particles. 

A scaled-up version of this central template-concentric sphere surface assembly approach has been demonstrated for the growth of multi-layer core-shell nano- and microparticles, based upon the repeated layer-by-layer deposition of linear polymers and silica nanoparticles onto a colloidal particle template (Figure 6.8) [60]. In this case, the regioselective chemistry occurs via electrostatic interactions, as opposed to the covalent bond formation of most of the examples in this chapter. The central colloidal seed particle dictates the final particle... 

The pair potential of colloidal particles, i.e. the potential energy of interaction between a pair of colloidal particles as a function of separation distance, is calculated from the linear superposition of the individual energy curves. When this was done using the attractive potential calculated from London dispersion forces, Fa, and electrostatic repulsion, Ve, the theory was called the DLVO Theory (from Derjaguin, Landau, Verwey and Overbeek). Here we will use the term to include other potentials, such as those arising from depletion interactions, Kd, and steric repulsion, Vs, and so we may write the total potential energy of interaction as... 

The literature suggests that the toxic effects of Thorotrast are due to the alpha radiation effects of thorium and not to the chemical effects of thorium or of the colloid (Faber 1973 BEIR IV 1988 Taylor et al. 1986 Wesch et al. 1983). Wesch et al. (1983) injected Thorotrast enriched with thorium-230 into rats and found a linear relationship between radiation level and tumor incidence. At a constant radioactive level, an increase in the injected colloidal volume had little influence on the number of liver tumors, but resulted in a decrease in tumor appearance time and, therefore, a decrease in lifespan. The larger colloidal volume may result in a more diffuse organ dose and a less "hot spot" distribution. Injection of the nonradioactive colloid resulted in no appreciable incidence of liver tumors. It is not known whether the colloidal particles induce the liver tumors when given in... 

For studying the stability of colloidal particles in suspension (Chapter 13) or for determining the potential at the surface of particles (Chapter 12), one often needs expressions for potential distributions around small particles that have curved surfaces. Solving the Poisson-Boltzmann equation for curved geometries is not a simple matter, and one often needs elaborate numerical methods. The linearized Poisson-Boltzmann equation (i.e., the Poisson-Boltzmann equation in the Debye-Hiickel approximation) can, however, be solved for spherical electrical double layers relatively easily (see Section 12.3a), and one obtains, in place of Equation (37),... 

A. which is due to reflection of the incident rays from the surfaces of the colloid particles, and which decreases with increase in the size of the particles. The product of the refractive index and the specific volume is a linear function of the concentration.1... 

Experimentally the increase in activation energy is quite evident, but the cause of this increase is not clear. It can be argued that the increase in activation energy is related to a strong increase in viscosity of the reactive medium or to phase separation in the reactive mass when a newly formed polymer precipitates from a solution and forms colloid particles. The experimental data described by Eqs. (2.23) - (2.25) can also be treated in ways other than those used in the original publication. For example, it is possible to linearize the exponential factor in Eq. (2.23), as was done above for other purposes. Then for the range of P from 0.35 to 0.8 we can write ... 

Particle asymmetry is a factor of considerable importance in determining the overall properties (especially those of a mechanical nature) of colloidal systems. Roughly speaking, colloidal particles can be classified according to shape as corpuscular, laminar or linear (see, for example, the electron micrographs in Figure 3.2). The exact shape may be complex but, to a first approximation, the particles can often be treated theoretically in terms of models which have relatively simple shapes (Figure 1.1). 

Electro- and magnetooptical phenomena in colloids and suspensions are widely used for structure and kinetics analysis of those media as well as practical applications in optoelectronics [143,144]. The basic theoretical model used to study optical anisotropy of the disperse systems is the noninteracting Brownian particle ensemble. In the frame of this general approximation, several special cases according to the actual type of particle polarization response to the applied field may be distinguished (1) particles with permanent dipole moments, (2) linearly polarizable particles, (3) nonlinearly polarizable particles, and (4) particles with hysteretic dipole moment reorientation. 

The sedimentation of pharmaceutical dispersions in non-Newtonian polymer solutions is of some practical interest. These polymers are used not only to stabilize colloidal particles but also to slow down (or prevent) settling, thus preventing cake formation. Newtonian fluids are defined as simple fluids that show a linear relationship between the rate of flow or shear (G) and the applied (or shearing) stress (F) at a constant viscosity (p) as shown in Figure 4.38 ... 

The relative rates of reaction for the hydrolysis and condensation dictate the structure and properties of an alkoxide gel. These reaction rates are schematically described in Figure 8.18 [43] for the example of a silicon ethoxide. In acidic solutions, hydrolysis is achieved by a bimolecular displacement mechanism that substitutes a hydronium ion (H" ) for an alkyl [44]. Under these conditions the hydroljreis is rapid compared to the condensation of the hydrolyzed monomers and promotes the development of larger and more linear molecules, as is described in Figure 8.19. Under basic conditions, hydrolysis occurs by nucleophilic substitution of hydrojgrl ions (OH ) for alkyl groups [45]. Here the condensation is rapid relative to hydrolysis, promoting the precipitation of three-dimensional colloidal particles as shown in Figure 8.17(b) and 8.19. 

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