Because of the importance of phospholipid rafts in cellular function and because of the utility of phospholipid membranes to probe phase transitions in confinement, transitions in phosphatidyl choline bilayers have long been a topic of interest.  Investigations of phase behavior often map the phase diagram in temperature-composition space, for 2 or 3 component systems.  When it comes to cell function, however, tension could be at least as important:  At fixed physiological temperature, cell functions regulate tension at least as high as 0.4 mN/m.  We report here the impact of tension on two-component phosphatidyl choline membranes.  While there is a general effect for elevated tensions to suppress phase separation as a result of the greater areal density of the solid phase, this happens in complicated ways, more dramatic than the calculated effects from Claussius Clapeyron.  Instead of the mere 0.3 C suppression of the phase separation temperature for each mN/m of applied tension, we report a dramatic change in the nature of the solid phases from patches / hexagon at low tensions to stripes at high tension, where the latter can selectively incorporate some tracers while the former do not.  We explain this effect based on a calculated triple point near the temperature range of interest.

Tension selects between membrane transitions resulting in striped or hexagonal domains

245th National Meeting (2013)

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