Barrier electrostatic

These findings show that the steric barrier provided by the 50 ft adsorbed films was inadequate to deflocculate the dispersion at all, even though it provided a million times more electrical resistance and reduced the viscosity very appreciably. On the other hand, the electrostatic barrier was very effective in deflocculating the system, but it took more dispersant than... 

The electrostatic barrier developed only after enough dispersant adsorbed that a concentration of dissolved dispersant of about 0.1% or more remained in the oil phase, where counterions developed as evidenced by increased conductivity, the development of large negative zeta potentials, steeply rising stability ratios, and complete deflocculation. 

For colloidal solutions, as a general rule, a barrier of 15-25kT is sufficient to give colloid stability, where the Debye length is also relatively large, say, greater than 20 nm. This electrostatic barrier is sufficient to... 

If the electrostatic barrier is removed either by specific ion adsorption or by addition of electrolyte, the rate of coagulation (often followed by measuring changes in turbidity) can be described fairly well from simple diffusion-controlled kinetics and the assumption that all collisions lead to adhesion and particle growth. Overbeek (1952) has derived a simple equation to relate the rate of coagulation to the magnitude of the repulsive barrier. The equation is written in terms of the stability ratio ... 

The neutron is a better hammer than the alpha particle for smashing nuclei. Being electrically neutral, it encounters no electrostatic barrier to penetrating the nucleus. Indeed, slow neutrons often And their way into nuclei more efhciently than fast ones, much as a slow cricket ball is easier to catch. So the discovery of the neutron, in the eyes of the veteran nuclear physicist Hans Bethe, marked a turning point in the development of nuclear physics. 

Space-Charge-Limited Diode. This method is equally applicable to electropositive and electronegative adsorbed layers. In a diode the maximum current which can be drawn from the cathode is given by the emission formula in Sec. V,A. Electrons emitted from the cathode at low current densities build up an electron atmosphere or space charge at the surface, and this space charge presents an electrostatic barrier to electrons flowing to... 

The different behavior of 7 and 8 is probably due to the charged head group in 7. Phase separation to form enriched domains of this lipid in mixed monolayers would be inhibited by electrostatic repulsion. Interestingly, mono-layer films of 7 mixed with the biologically important molecule cholesterol did exhibit phase separation at all compositions provided the temperature was maintained below the Tm of 7. Presumably the significantly different shapes of the two molecules promotes the phase separation and overcomes the electrostatic barrier. 

Ions with the same charge as the resin are excluded. (The quaternary ammonium resin excludes K+.) The counterion, Cl, is not excluded from the resin. There is no electrostatic barrier to penetration of an anion into the resin. Anion exchange takes place freely in the quaternary ammonium resin even though cations are repelled from the resin. 

It is well-known that protein adsorption tends to be at a maximum at the isoelectric point because the protein has zero net charge. Under such conditions, electrostatic barriers to adsorption are minimized. 

Aftertreatment The wetfastness of dyeings produced with acid dyes is often unsatisfactory. Formerly, tannic acid and tartar emetic were used, which form a 1 1 adduct on the material by hydrogen bonding. This process is expensive and said to be carcinogenic. Synthetic tanning agents (Synthanes) are preferred. They are condensation products of aromatic sulfonic acids with formaldehyde [106] or of phenols with formaldehyde, which are made water-soluble by reaction with bisulfite. These products deposit on the fiber surface and form an electrostatic barrier... 

The interactions of charged oligomeric radicals with charged particles needs to be studied in greater detail, since these affect the rate of capture, R. What is the magnitude of the "tunneling effect" in overcoming the electrostatic barrier Can... 

As a result of (a), an electrostatic barrier restricts the rotation, thus increasing the life-time of the zwitterionic conformer (112), and it was suggested that the rate of elimination of N from (112) is higher than the rate of internal rotation (k l2)>k l2)) (Rappoport etal., 1963). Moreover, the nucleophilicity of the electron pair on the a-carbon atom decreases by interaction with the positive charge and, when rotation around the Ca—bond takes place, conformer (113) is traversed rapidly and, once (114) is obtained, thermodynamic control takes over. 

In addition, as a result of (b), protonation may be faster than the 60° rotation, forming (115) in an almost concerted cis addition. In (115) the electrostatic barrier to rotation disappears, and rotation could again be faster than the elimination of HX, resulting in thermodynamic control. 

The diffusion of the reactants to form the encounter complex (Kdif) may involve electrostatic barriers [38]. The following expression takes into account these Coulombic interactions [34] ... 

The ability of micelles to enhance photoionization yields of hydrophobic molecules was demonstrated in the early 1970s. Thus, the photoionization yields of pyrene [59], phenothiazine [60] and tetramethylbenzidine [61] cations increased when these molecules were encapsulated in anionic micelles. The effect was attributed to efficient escape of electrons from the geminate charge-separated species formed within the micelle, which is accelerated by the anionic interface. The negative micellar surface imposes an electrostatic barrier between the cations, which remain with the micelle, and the aqueous electron in the bulk water phase, thus increasing the lifetimes of the photoredox products. 

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