Colloidal electronic nature

Real charge is always associated with well-defined physical carriers such as electrons and ions this is not so for the idealized physical charge considered in electrostatics. Each conductor can be characterized by stating the nature and concentration of the free charges. In the present section we consider free charged particles of atomic (or molecular) size, not larger, aggregated entities, such as colloidal particles. 

As mentioned above, compact DNA molecules behave just like a soluble colloid, where the inner part of the compact structure is almost electronically neutralized and the surface is negatively charged. Such colloidal behavior is rather general regardless of the chemical nature of the condensing agents, such as multi-valent... 

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). 

Baalousha, M., Kammer, F. V. D., Motelica-Heino, M., Baborowski, M., Hofmeister, C., and Le Coustumer, P. (2006). Size-based speciation of natural colloidal particles by flow field flow fractionation, inductively coupled plasma-mass spectroscopy, and transmission electron microscopy/x-ray energy dispersive spectroscopy Colloids-trace element interaction. Environ. Sci. Technol. 40(7), 2156-2162. 

The experimental detection and quantitation of surface species on soil particles and other natural colloids is a difficult area of research because of sample heterogeneity, low surface concentrations and the need to investigate solid adsorbents in the presence of liquid water. Unambiguous information about the molecular structure and stability of adsorbed species can be obtained only with in situ surface spectroscopy (see also Chapter 3). Invasive spectroscopic methods that require sample desiccation or high-vacuum techniques (e.g. electron microscopy, X-ray... 

To verify the effect of the ions adsorption on the regularities of photoexcitation relaxation, we studied the temperature effect on the kinetics of the ultradispersed CdS photobleaching relaxation at the addition of electron acceptors of various nature. Fig. 2.13 presents the kinetic curves of the colloidal CdS photobleaching relaxation prepared with an excess of cadmium ions at different temperatures and at the addition of different... 

Studies on luminescence of CdS colloids provide useful knowledge on the energy and nature of recombination sites of charge carriers in the colloidal particles. The regularities of the colloid photoluminescence quenching provide the information on the dynamics of electrons and holes in semiconductor particles as well as on the kinetics of interfacial electron transfer. Of a particular interest are studies on the luminescence of colloidal solutions of the so-called Q-semiconductors, their properties depending on the size of semiconductor particles due to the quantum size effects. 

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