Gibbs absorption

Using the Gibbs absorption equation and assuming Henry s law (eq. 3.42)... 

Figure D3.5.5 Equilibrium surface tension of sodium dodecyl sulfate (SDS) at the air-water interface as a function of surfactant concentration. The corresponding surface coverage was calculated using the Gibbs absorption equation (Eq. D3.5.26).

Surface films also form on solutions of soluble surfactant. In that case, the surface tension isotherm is measured as a function of concentration of surfactant in the solution. The surface pressure isotherm can be basically understood by the Gibbs absorption isotherm, which in the particular case of air-water interface relates the change of the surface tension to the chemical potential of the surfactant as ... 

A is the area of the surface. In a foam, where the surfaces are interconnected, the time-dependent Marangoni effect is important. A restoring force corresponding to the Gibbs elasticity will appear, because only a finite rate of absorption of the surface-active agent, which decreases the surface tension, can take place on the expansion and contraction of a foam. Thus the Marangoni effect is a kinetic effect. 

The adsorption T depends on the position of the Gibbs dividing surface and it is therefore convenient to define a new function, the relative adsorption, that is not dependent on the dividing surface. The absorption of component i at the interface is defined by eq. (6.3) as... 

Moisture vapor transmission rate (MVTR), for VDC copolymers, 25 709-710 Molality, 15 751 Molar absorptivity, 14 237 Molar flux, 15 678 Molar Gibbs energy, 24 660, 662 Molarity, 15 751... 

Cao XH, Gibbs ST, Fang LY, Miller HA, Landowski CP, Shin HC, Lennernas H, Zhong YQ, Amidon GL, Yu LX and Sun DX (2006) Why Is It Challenging to Predict Intestinal Drug Absorption and Oral Bio availability in Human Using Rat Models. Pharm Res 23 pp 1675-1686. 

When an adsorbing surface is exposed to a gas or vapour adsorption will take place, being accompanied by the absorption or evolution of heat. Such thermal changes have already been noted in the extension and contraction of surface films of liquids. Although the direct determination of the surface energy of solid surfaces presents many experimental difficulties yet of its existence there is no doubt. On the adsorption of a gas or vapour a diminution in the free surface energy of the system likewise occurs. From the Gibbs-Helmholtz relationship dcr... 

Similar data for the two-component system water-ammonia are also available and complete, because of the use of this system in absorption refrigeration. The data of Scatchard and coworkers are the most recent 24), and are unique among such compilations in that the availability function is tabulated as well as the usual enthalpy, entropy, and Gibbs free energy. These data have been converted to graphical form (charts) by Kohloss and Scott 16) and Bulkley and Swartz 4). Older data, but more complete in the low concentration range, are those of Jennings and Shannon 11). 

Isogibberellic Acid (gibb-4-ene 1 —> 3 lactone). This compound exhibits a small absorption at 254 m/, but as it is unchanged by the conditions employed for the decomposition of gibberellic acid, no complication is introduced by its presence. 

Figure 6.3 Effects of hydrocarbon chain modifications on melting points of similar-sized cuticular lipids. When lipids melt, the absorption frequency of C-H symmetric stretching vibrations increases from -2849 cm1 to -2854 cm4. From right to left, compounds are (chemical change relative to n-alkane, molecular mass in daltons) filled circles, n-dotnacontane (no change, 450) open circles, palmitic acid myristyl ester (wax ester, 452) filled triangles, 13-methylhentriacontane (methyl-branched alkane, 450) open triangles, (Z)-13-tritriacontene (double bond, 462) filled squares, 9,13-dimethylhentriacontane (2 methyl branches, 464) open squares, oleic acid oleyl ester (2 double bonds and an ester link, 532). Data from Gibbs and Pomonis (1995) and Patel el al. (2001).

The expression for the excess Gibbs energy is built up from the usual NRTL equation normalized by infinite dilution activity coefficients, the Pitzer-Debye-Hiickel expression and the Born equation. The first expression is used to represent the local interactions, whereas the second describes the contribution of the long-range ion-ion interactions. The Bom equation accounts for the Gibbs energy of the transfer of ionic species from the infinite dilution state in a mixed-solvent to a similar state in the aqueous phase [38, 39], In order to become applicable to reactive absorption, the Electrolyte NRTL model must be extended to multicomponent systems. The model parameters include pure component dielectric constants of non-aqueous solvents, Born radii of ionic species and NRTL interaction parameters (molecule-molecule, molecule-electrolyte and electrolyte-electrolyte pairs). 

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