Absence of a vestigial vapor pressure parades

The enigmatic but much accepted vapor pressure paradox for oriented lipid b ilayer samples was recently justified theoretically. Subsequently, recent e xperiments have shown that there is no vapor pressure paradox. The first re sult of this paper is to consider another degree of freedom that reverses t he previous theoretical conclusion, so that theory and experiment are now i n agreement that there is no vapor pressure paradox. However, this analysis also suggests the possibility of a vestigial vapor pressure paradox that w ould rationalize why the vapor pressure paradox was historically so persist ent and that would have led to an improved protocol for obtaining bilayer s tructure. This vestigial vapor pressure paradox would involve a phase trans ition as a function of applied osmotic pressure. We test this possibility e xperimentally using combined neutron and x-ray scattering data. The conclus ion from these experiments is that there is not even a vestigial vapor pres sure paradox. However, this negative result validates an improved method fo r calibrating osmotic pressure in x-ray studies of oriented samples.