Calculations contact energy surfaces

Maa (M2) developed a procedure for calculating the liquid surface temperature as a function of the time each liquid element is in contact with the vapor. He assumed that the latent heat of vaporization is transferred from the interior of the liquid to the interface by pure conduction. Consequently, the sole source of energy for vaporization is the sensible heat made available by a change in the liquid temperature. If exposure time is short, only the liquid near the surface will undergo a temperature change. The heat transfer within the liquid is modeled by... 

The first high-level theoretical evidence for the existence of dihydrogen bonds between CH4 and [NH4]+ came in 1996 [5]. In the sense of bonding geometry, this complex is not linear (Structure 6.5), has Csv symmetry, and exhibits three relatively short H- -H contacts with distances of 2.237, 2.357, and 2.226 A calculated at the RHF/6-31G, RHF/6-311++G, and MP2/6-31G lev-els, respectively. According to the frequency analysis at the RHF/6-31G level, the complex occupies a minimum on the potential energy surface of this system. The BSSE-corrected interaction energies have been calculated as —2.46,... 

We have now collected almost all the pieces required for a first version of COSMO-RS, which starts from the QM/COSMO calculations for the components and ends with thermodynamic properties in the fluid phase. Although some refinements and generalizations to the theory will be added later, it is worthwhile to consider such a basic version of COSMO-RS because it is simpler to describe and to understand than the more elaborate complete version covered in chapter 7. In this model we make an assumption that all relevant interactions of the perfectly screened COSMO molecules can be expressed as local contact energies, and quantified by the local COSMO polarization charge densities a and a of the contacting surfaces. These have electrostatic misfit and hydrogen bond contributions as described in Eqs. (4.31) and (4.32) by a function for the surface-interaction energy density... 

Picosecond absorption spectroscopy studies of the contact ion pairs formed in the photo-initiated, S N 1 reaction of three substituted benzhydryl acetates (18) provided the rate constants for the k and k2 steps of the reaction (Scheme 10), in acetonitrile and DMSO.83 The activation parameters for the k and k2 steps were obtained from the temperature dependence of these steps and the transition state energies were calculated from the rate constants. This allowed the energy surfaces for three substituted substrates to be calculated in each solvent. The effect of solvent reorganization on the reactions of the unsubstituted and methyl-substituted benzhydryl contact ion pairs (CIP) was significant, causing a breakdown of transition state theory for these reactions. The results indicated that it will be very difficult to develop a simple theory of nucleophilicity in, S N1 reactions and that Marcus theory cannot be applied to SnI processes. 

In the case of physical bonds (London dispersion, Keesom orientation, and Debye induction forces), the energy of interaction or reversible energy of adhesion can be directly calculated from the surface free energies of the solids in contact. 

For both models, it is possible to calculate the energy landscape generated by relative translation analytically. Both times it is found that (i) Tj = Fg/A is independent of A if the two periods of the two surfaces match, (ii) Tj decreases as A if the two surfaces are random, and (iii) Tj is zero if the surfaces are incommensurate. Contributions from the circumference of finite contacts between incommensurate surfaces yield contributions to that vanish with a higher power law than A (see also Fig. 6). 

Use of the interaction parameter to correct for non-linearities present in plots of cose vs Jlv resulted in the following equations (Eq. 6,7)(Neumann et al, 7, 8) which represent a great advance in bringing surface chemistry within experimental reach, and allow calculation of solid surface energies from easily measured contact angles and liquid surface energies. Equation 6 is cubic in and some care must be taken in selecting the... 

Three methods are usually used to calculate contact angle—Wilhelmy plate method, sessile drop method [33], and captive bubble method [34]. Sessile drop method is the most commonly used method for biomedical polymers. In this method, about 3 pi of a liquid droplet is placed on the polymer surface and images of the drop are acquired about 30 s of equilibration of the drop. Interface energy between the solid sample snrface and hqnid can also be calculated using the Young s eqnation ... 

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