Interaction potentials strength

When an atom or molecule approaches a surface, it feels an attractive force. The interaction potential between the atom or molecule and the surface, which depends on the distance between the molecule and the surface and on the lateral position above the surface, detemiines the strength of this force. The incoming molecule feels this potential, and upon adsorption becomes trapped near the minimum m the well. Often the molecule has to overcome an activation barrier, before adsorption can occur. 

According to Hess, the relative strength of the entanglement friction can be related to the more microscopic parameter q , describing the range of the true interchain interaction potential. A value of q 1 = 7 A, close to the average interchain distance of about 4.7 A, is obtained. 

Less is known about the interaction of the nucleosomes between themselves or with free DNA. The nucleosome-nucleosome interaction has recently been parameterized by using the surface charge density of the known crystal structure [39] in a point-charge model [51]. While in that work only electrostatic interactions were considered and the quantitative influence of the histone tails on the interaction potential still remains obscure, simulations based on this potential allowed to predict an ionic-strength dependent structural transition of a 50-nucleosome chromatin fragment that occurred at a salt concentration compatible with known experimental data (Ref. [65], see below). 

From the functional form of Eq. 12.5, it is easy to see that as distance between the molecules rjj becomes small, the potential becomes very repulsive due to the dominance of the first term (r 12 dependence). However, the repulsive term drops off very rapidly with distance, and the attractive term dominates at long distances. The interaction potential has a minimum at some intermediate distance, with a characteristic attractive well-depth. The parameter oij represents a net collision diameter, and etj determines the depth (strength) of the interaction. Methods for obtaining these parameters from experiment and other estimation techniques are discussed in Section 12.2.3. Combining rules to estimate the parameters interactions between unlike molecules are given in Section 12.2.4. 

Flexible polyelectrolytes exhibit conformational variations when the interaction strength (ZB) or the density of a system is changed. Hence, the structure factor is no longer an a priori known quantity but has to be determined in a self-consistent manner. This is achieved by casting the underlying multichain interactions into a medium-induced interaction potential among the... 

A pair of polysaccharide molecules approaching each other in water exerts an interaction potential ( ) that is the algebraic sum of the competing attractive and repulsive forces. integrated over all pairs of molecules, is . This principle is embodied in the Deijaguin-Verwey-Landau-Overbeek (DLVO) theory of colloidal stability (Ross and Morrison, 1988). The equilibrium distance between the molecules is related to c, the volume of the hydrated particles, ionic strength, cosolute, nonsolvent additions, temperature, and shearing. 

In this paper it is shown that the rate of deposition of Brownian particles on the collector can be calculated by solving the convective diffusion equation subject to a virtual first order chemical reaction as a boundary condition at the surface. The boundary condition concentrates the surface-particle interaction forces. When the interaction potential between the particle and the collector experiences a sufficiently high maximum (see f ig. 2) the apparent rate constant of the boundary condition has the Arrhenius form. Equations for the apparent activation energy and the apparent frequency factor are established for this case as functions of Hamaker s constant, dielectric constant, ionic strength, surface potentials and particle radius. The rate... 

The effect of electrolyte concentration on the transition from common to Newton black films and the stability of both types of films are explained using a model in which the interaction energy for films with planar interfaces is obtained by adding to the classical DLVO forces the hydration force. The theory takes into account the reassociation of the charges of the interface with the counterions as the electrolyte concentration increases and their replacements by ion pairs. This affects both the double layer repulsion, because the charge on the interface is decreased, and the hydration repulsion, because the ion pair density is increased by increasing the ionic strength. The theory also accounts for the thermal fluctuations of the two interfaces. Each of the two interfaces is considered as formed of small planar surfaces with a Boltzmannian distribution of the interdistances across the liquid film. The area of the small planar surfaces is calculated on the basis of a harmonic approximation of the interaction potential. It is shown that the fluctuations decrease the stability of both kinds of black films. 

It should be noted that many attempts have been made to explain the hydration force by microscopic models. For example, the disagreements between experiment and the traditional mean field theory were attributed to the ion-ion correlations (ignored by the mean field theory) one of the most successful theories is based on the anisotropic hyper-netted chain method [23], It was shown on the basis of that theory that an additional repulsion (similar to the hydration force) can indeed occur at small separations and large ionic strengths [24], However, the results are so strongly dependent on the choice of the interaction potentials between the ion-pairs, that even a double layer attraction could be predicted [25], In addition, the hydration force in the absence of an electrolyte, or at moderate ionic strength, could not be explained by this model. 

Microemulsions consist of oil, water and an oil-water interfacial Him. DLS and SLS have been used to determine the translational diffusion coefficient and the interaction potential of microemulsions [45—47). The thickness of the inter-facial film and its curvature were measured by the contrast variation method in neutron scattering [48,491. This method is based on changing the scattering strength by changing the relative amount of light and heavy water in the microemulsion. 

Information concerning the interaction potentials of Cs (7S, 5D)-rare gas pairs is obtained by interpreting the temperature dependence of the 6S-7S,5D far wing and satellite profiles. A sensitive laser fluorescence technique is used to obtain the absorption coefficient of the mixture. The collision induced oscillator strength, a rapidly varying function of the interatomic distance in the case of such forbidden transitions, is also deduced. Experimental potentials and oscillator strengths are compared with available calculated values. 

Typical ionic interactions are strong on a thermal energy scale. We can characterize the strength of these interactions by considering the distance between monovalent ions when their mutual interaction potential energy corresponds to the standard thermal energy T = 298 K) r = 561 A. Because these inter-... 

In Figure 2 the pure-component adsorption isotherms of methane and ethane in SWNTs are presented as an amount adsorbed per unit volume of the pore. At low pressures the greatest adsorption occurs in the small pores. This is due to smaller pores having larger adsorbate-adsorbent interaction potentials. Small pores fill rapidly, even low pressure, due to the presence of a strong wall potential function. The complex variation between the isotherms for different pore sizes is caused by a trade-off between the strength of methane-SWNTs interaction and the ability of SWNTs to accommodate methane... 

---