Electrostatic energy barrier

Elimelech, M., and Ch. R. O Melia (1990), "Effect of Particle Size on Collision Efficiency in the Deposition of Brownian Particles with Electrostatic Energy Barriers", Langmuir 616,1153-63. 

The foregoing discussion, in emphasizing the purely electrostatic energy barriers, does not address the question of whether there is an activation advantage in thiol esters relative to oxygen esters. Why thiol esters in preference to oxygen esters Thiol esters are more readily enolized than... 

The magnitude of the electrostatic contribution to stabilization of the dispersion against flocculation can be determined from the electrostatic energy barrier shown in Figure 2, a plot vs. interparticle distance H of the electrostatic repulsion plus the dispersion force attraction term, U 0, (in units of kT at 20°C). 

The result of such extended electrostatic energy barriers in... 

Figure 2. Electrostatic energy barrier between two carbon particles in oil with micellar dispersant. Conditions ip0, —ISO mV 1/k, 59A

The kinetics of deposition can be modeled as an activated process, and the rate of deposition will depend on the energy barrier height, A F. To examine the functional dependence of A on various experimental parameters, we consider that the interaction potential between the charged DNA-SWCNTs and the substrate consists of two components, electrostatic repulsion and van der Waals attraction, as in DLVO theory. The interaction potential depends on separation between, and relative orientation of, the DNA-SWCNT and the surface. The potential barrier is lowest when the axis of the DNA-SWCNT is perpendicular to the surface. This has been confirmed numerically we have previously examined deposition by thermal hopping over an electrostatic energy barrier of DNA-SWCNT rods aligned parallel to the substrate" in order to explain a different set of experiments, and the potential barrier can be far higher. 

When the electrostatic energy barrier is overcome, the films can still be stabilized at extremely low thickness (<0.5 nm) via entropic confinement forces (steric forces). Such extremely thin films are then called Newton Black films. The solvation forces are then typically due to molecular structure in the liquid that plays a role when the film is thinner than several molecular diameters, and can be either attractive or repulsive. An example is the repulsive hydration force due to water hydrogen bonding with the polar head group of a surfactant molecule adsorbed to the liquid-vapor interface (7, 8). 

Thus, the work function is represented by a difference between electrostatic energies and /teh. which contains kinetic, exchange, and correlation energy terms. 4> consists of an electrostatic energy barrier Au for the removal of an electron from the semi-infinite metal, and the chemical potential 7tch> which represents the energy difference between a free electron at electrostatic potential and the... 

Thus, the results shown in Figure 11.10 furnish direct support for the heterogeneity hypothesis often used to interpret colloid particle deposition kinetics under a barrier-controlled deposition regime [73]. In these experiments, particle deposition kinetics were determined as a function of salt concentration added to reduce the electrostatic energy barrier. Measured deposition rates were found by orders of... 

What other factors might be responsible for difference in activation energies Compare atomic charges anc electrostatic potential maps for the Sn2 transition states Does the increase in steric crowding lead to enhanced o diminished charge delocalization Explain. How, if at all would this be expected to affect the energy barrier Why ... 

Figure 1. The tunneling of a single electron (SE) between two metal electrodes through an intermediate island (quantum dot) can be blocked of the electrostatic energy of a single excess electron trapped on the central island. In case of non-symmetric tunneling barriers (e.g. tunneling junction on the left, and ideal (infinite-resistance) capacitor on the right), this device model describes a SE box .

At a finite distance, where the surface does not come into molecular contact, equilibrium is reached between electrodynamic attractive and electrostatic repulsive forces (secondary minimum). At smaller distance there is a net energy barrier. Once overcome, the combination of strong short-range electrostatic repulsive forces and van der Waals attractive forces leads to a deep primary minimum. Both the height of the barrier and secondary minimum depend on the ionic strength and electrostatic charges. The energy barrier is decreased in the presence of electrolytes (monovalent < divalent [Pg.355]

In such systems the requirement of the electrostatic contribution to colloidal stability is quite different than when no steric barrier is present. In the latter case an energy barrier of about 30 kT is desirable, with a Debye length 1/k of not more than 1000 X. This is attainable in non-aqueous systems (5), but not by most dispersants. However when the steric barrier is present, the only requirement for the electrostatic repulsion is to eliminate the secondary minimum and this is easily achieved with zeta-potentials far below those required to operate entirely by the electrostatic mechanism. 

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