Model membranes, transport through

Fig. 13.3. Model of transport through a glass membrane m and m" are hydrated layers, and m the interior of the membrane.

Reprinted from Chemical Engineering Journal, 64, P.J.A.M. Kerkhof, A modified Maxwell-Stefan model for transport through inert membranes the binary friction model, 319-344,1996, with kind permission from Elsevier Science S.A., P.O. Box 564,1001 Lausanne, Switzerland. 

Figure 9.11 Net pressure difference in the counterdiffusion of N2 and CjH4. Symbols show the experimental data of Waldmann and Schmitt [11] drawn line show simulation with the binary friction model. Highest pressure on the nitrogen side. The DGM predicts no pressure difference (from Kerkhof [5]). Reprinted from Chemical Engineering Journal, 64, PJ.A.M. Kerkhof, A modified Maxwell-Stefan model for transport through inert membranes the binary friction model, 319-344,1996, with kind permission from Elsevier Science S.A., RO. Box 564,1001 Lausanne, Switzerland.

Dunker, A. K., and Marvin, D. A., A model for membrane transport through a-helical protein pores, J. Theor. Biol. 72, 9-16 (1978). 

As with anthraphyrin vide supra), direct measurements of affinity constants were made as a way of complementing the basic yes, it binds anions conclusions obtained from the sapphyrin-predicated through-model-membrane transport studies described above. In general, the requisite measurements were made by... 

A general model for transport through porous crystal membranes was described by Barter [35]. The model involves five steps (Fig. 7) ... 

We are attempting to computer model ion transport through Nations by generating sample membrane cubes. These cubes contain the structures determined from our theory of ionomer structure. Once a sample cube is generated, we computer simulate the migration of solvated anions (OH") and cations (Na+) through the membrane sample cube under the potential of an applied field. Electrostatic and diffusion interactions are computed with respect to the explicit structure of the sample... 

P.J.A. M. Kerkhof A Modified Maxwell-Stefan Model for Transport through Inert Membranes The Binary Friction Model, Chem. Eng. J. 64 319-343 (1996). 

Ultrafiltration separations range from ca 1 to 100 nm. Above ca 50 nm, the process is often known as microfiltration. Transport through ultrafiltration and microfiltration membranes is described by pore-flow models. Below ca 2 nm, interactions between the membrane material and the solute and solvent become significant. That process, called reverse osmosis or hyperfiltration, is best described by solution—diffusion mechanisms. 

A generalized model of transport allowing for component interactions is provided by nonequilibrium thermodynamics where the flux of component i through the membrane /, [gmol/(cm -s)] is written as a first-order perturbation of the chemical potential dp,/dx [cal/(gmohcm)] ... 

The favourable properties which mark out vesicles as protocell models were confirmed by computer simulation (Pohorill and Wilson, 1995). These researchers studied the molecular dynamics of simple membrane/water boundary layers the bilayer surface fluctuated in time and space. The model membrane consisted of glycerine-1-monooleate defects were present which allowed ion transport to occur, whereby negative ions passed through the bilayer more easily than positive ions. The membrane-water boundary layer should be particularly suited to reactions which are accelerated by heterogeneous catalysis. Thus, the authors believe that these vesicles fulfil almost all the conditions required for the first protocells on earth ... 

All of the above considerations have sometimes led to a too rigid picture of the membrane structure. Of course, the mentioned types of fluctuations (protrusions, fluctuations in area per molecule, chain interdigitations) do exist and will turn out to be important. Without these, the membrane would lack any mechanism to, for example, adjust to the environmental conditions or to accommodate additives. Here we come to the central theme of this review. In order to come to predictive models for permeation in, and transport through bilayers, it is necessary to go beyond the surfactant parameter approach and the fluid mosaic model. 

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