Like-charged objects

In this discussion of colloid stability we will explore the reasons why colloidal dispersions can have different degrees of kinetic stability and how these are influenced, and can therefore be modified, by solution and surface properties. Encounters between species in a dispersion can occur frequently due to any of Brownian motion, sedimentation, or stirring. The stability of the dispersion depends upon how the species interact when this happens. The main cause of repulsive forces is the electrostatic repulsion between like charged objects. The main cause of attractive forces is the van der Waals forces between objects. 

Contrary to the simulations, the osmotic coefficient from the PB theory is always positive. This has led to the general question whether there could be an attraction between like-charged objects within PB theory. Very recently it has been proved that such attractive interactions are absent on the PB level [43]. An extension of this statement to ions of finite size and to a wider class of boundary conditions can be found in Ref. 44. A fairly general statement in this context is the following In any local density functional theory, in which the charge density p and the electrostatic potential >l> satisfy the inequality dp/dtfj < 0, the pair interactions are repulsive. 

Two approaching emulsion droplets may be resisted by electrostatic forces. Electrostatic forces consist of Coulombic repulsion between two like charged objects and attractive van der Waals forces. These two forces are accounted for by the Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory. A third force. Born repulsion, occurs at very small separation distances when electron clouds overlap [1,6,20,21], In emulsion systems an electrical double-layer may form around the disperse phase droplets. While electrical double-layer repulsion is certainly important in o/w emulsions, it does not play a large role in the stabilization of w/o emulsions due to the low dielectric constant of oil [55,56],... 

Ordinarily we expect like-charged objects (such as protons) to repel each other. The forces holding protons and neutrons together in the nucleus are very much stronger than ordinary electrical forces (Section 25-6). 

Electrostatics is the study of interactions between charged objects. Electrostatics alone will not described molecular systems, but it is very important to the understanding of interactions of electrons, which is described by a wave function or electron density. The central pillar of electrostatics is Coulombs law, which is the mathematical description of how like charges repel and unlike charges attract. The Coulombs law equations for energy and the force of interaction between two particles with charges q and q2 at a distance rn are... 

In the 1920s it was found that electrons do not behave like macroscopic objects that are governed by Newton s laws of motion rather, they obey the laws of quantum mechanics. The application of these laws to atoms and molecules gave rise to orbital-based models of chemical bonding. In Chapter 3 we discuss some of the basic ideas of quantum mechanics, particularly the Pauli principle, the Heisenberg uncertainty principle, and the concept of electronic charge distribution, and we give a brief review of orbital-based models and modem ab initio calculations based on them. 

A charged object immersed in an electrolyte solution attracts ions of opposite charge and repels ions of like charge, thereby creating an electrical double layer. Thus, the resistance of two colloidal ions to coagulation is due primarily to repulsion of the interpenetrating electrical double layers. 

Figure 9b shows a schematic of the DNA bundle phase observed at MVLBisG2 > 0.5. The bundling phase requires the presence of salt (as found in the cell culture medium used for all our experiments) and is formed by the interplay of the salt-induced screening of the electrostatic interactions and the depletion-attraction [59,60] caused by the lipid micelles. While depletion-attraction has previously been reported for like-charged or neutral objects, the screening of the electrostatic interactions also... 

The DLVO theory [1,2], which describes the interaction in colloidal dispersions, is widely used now when studying behavior of colloidal systems. According to the theory, the pair interaction potential of a couple of macroscopic particles is calculated on the basis of additivity of the repulsive and attractive components. For truly electrostatic systems, a repulsive part is due to the electrostatic interaction of likely charged macroscopic objects. If colloidal particles are immersed into an electrolyte solution, this repulsive, Coulombic interaction is shielded by counterions, which are forming the diffuse layer around particles. A significant interaction occurs only when two double layers are sufficiently overlapping during approach of those particles. 

The kinetic consideration outlined here is very similarly based on empirical properties of metal ions which (although loosely) correspond to their a-and TT-bonding capacities and - directions like with Hammett s approach (Hammett 1973 Schiiiirmann 1991) for reaction kinetics in benzenoid aromatics. In either case, there is no precise link as yet with electronic parameters closely defined in quantum chemistry like charge density, as the principal objective by now is to understand reactions kinetics and thus selection of certain catalysts, discriminating against others. 

In all cases, the variability for the PDQC charges in Table 2 is highest for the central carbon atom. As Woods et al. note, the exposure of the van der Waals surface of the methanol carbon atom is quite limited. As a result, the electrostatic potential will be more sparsely sampled in this region and perhaps therefore will not be as well described by the final parameters. Classical electrostatics is likely playing a role here as well. Classically, all the charge on a charged object is found on the surface of the object. Because class III charge... 

He 2 Alpha Particle—The alpha particle is identical in composition (with 2 protons and 2 neutrons) to the nucleus of a helium atom. It is also important to note that, like a bare helium nucleus, the alpha particle is positively charged and will be attracted to a negatively charged object. 

Charged objects in most cases are dissolved in water. Like any material. 

Scientists have discovered through observation that objects with like charges, whether positive or negative, repel each other, and objects with unlike charges attract each other. 

Simulation studies and theoretical developments of other systems show that short-range attraction also may appear between like-charged planes [38-40], cylinders [37,41-48], and stiff chains [49]. Attraction arising from electrostatic interactions among like-charged flexible objects has also been documented. For example, such an attraction gives rise to chain collapse [50-53] and phase instability [54] in systems containing flexible... 

---