Surface phenomena transient states

While the above system is an example where two-dimensional phase separation in the sense of Fig. la,b (or Fig. 5) occurs, there exist also good examples where no lateral phase separation exists in equilibrium, and the system forms a single interface parallel to the surfaces (Fig. Id). However, if one chooses the initial state such that the phase preferred by air is close to the substrate and the phase preferred by the substrate is next to the air surface [77], the system is unstable and surface phase inversion takes place. A laterally inhomogeneous state then occurs only as a transient phenomenon necessary to trigger the inversion kinetics, but not as an equilibrium state [77]. 

In the lipid bilayer systems, since the membrane molecules are arranged in such a way that the charged groups face a water phase and the interior of the membrane is a hydrocarbon phase, the contribution of surface potential to the membrane potential is important. It should be mentioned that the contribution of surface potential to the membrane potential, as discussed above, is generally a transient one in these systems. However, since the electrical conductance due to ion permeation across the lipid bilayer membrane is very low, we can observe the transient potential difference as a quasi-steady state phenomenon. However, if a constant ion distribution is restored by a transport process with a nonelectrical current (active transport) and maintained continuously, the above membrane potential process could become a steady state process. 

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