Planar water-hydrocarbon surface

In solutions of water and surfactant, the surfactant monolayers can join, tail side against tail side, to form bilayers, which form lamellar liquid crystals whose bilayers are planar and are arrayed periodically in the direction normal to the bilayer surface. The bilayer thickens upon addition of oil, and the distance between bilayers can be changed by adding salts or other solutes. In the oil-free case, the hydrocarbon tails can be fluidlike (La) lamellar liquid crystal or can be solidlike (Lp) lamellar liquid crystal. There also occurs another phase, Pp, called the modulated or rippled phase, in which the bilayer thickness varies chaotically in place of the lamellae. Assuming lamellar liquid crystalline symmetry, Goldstein and Leibler [19] have constructed a Hamiltonian in which (1) the intrabilayer energy is calculated... 

This conclusion compares favorably with what is known from studies of the adsorption of P-casein on to air/liquid, liquid/liquid, and solid/liquid interfaces using a range of other techniques. It has generally been found that the adsorbed amount of P-casein on hydrophobic surfaces is between 2 and 3 mg m over a wide range of bulk concentrations. This is the case for planar air/water and planar oil/water interfaces (59), for hydrocarbon oil/water interfaces in emulsions (64), and for interfaces between water... 

Fig. 4 Intermolecular forces vs. distance between a sphere (with a radius of 50 nm) and flat surfaces. Solid curve both sphere and planar surface are terminated by hydrocarbon groups across water as a medium, with a Hamaker constant of 4.5 x 10 J ([113], pg 189). Dashed curve both sphere and planar surface are modified with bUayer surfaces composed of the uncharged sugar-headgroup lipid, monogalactosyl diglyceride in 0.15 M NaCl, with a Hamaker constant of 3.5 x 10 J ([113], pg 396) (source Zou S., private communication)...

The simulations revealed a picture of ion permeation that is in sharp contrast with the continuum dielectric model. As the ion moves across the water-membrane interface into the bilayer, the membrane surface does not remain approximately planar. Instead, a local deformation is formed in which water molecules and polar head groups (normally restricted to the surface of the membrane) follow the ion into the nonpolar interior of the bilayer. Once the ion crosses the midplane of the membrane, the deformation on the incoming side relaxes and simultaneously, a similar deformation forms on the outgoing side. Thus, during the entire transfer process, the ion remains partially solvated by both the polar head groups and water molecules. The key feature of this molecular description of the ion transfer process is that the ion is never fully solvated by the nonpolar hydrocarbon tails. Thus, the calculated is markedly lower than the barrier predicted from the continuum model. For Na", was estimated at... 

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