Reverse transmembrane pressure difference

In separation terms, membranes were developed as thin, flexible semi-permeable sheets of regenerated cellulose material, intended to separate species at the molecular and ionic level, their first main application being in the purification of salt and brackish waters by reverse osmosis - which is not a filtration process, but one relying on different rates of diffusion for water and ions through the membrane material under high transmembrane pressure. 

In an elegant modeling study of lipid bilayers, Yagisawa et al. showed that oscillations can be induced by a transmembrane pH and salt gradient, with no electrical stimulation or pressure gradients [51]. Briefly, the pH difference leads to a transmembrane dipole and electrical stress on the nonpolar interior of the bilayer, triggering a gel/liquid crystal transition. Following this transition, permeability to salt increases and there is a relaxation of electrical stress, followed by reversal of the lipid transition, restoration of membrane potential, and reinitiation of the cycle. 

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