On the formation of a macroscopically flat phospholipid membrane on a hydrosol substrate

The dependence of the structure of a phospholipid layer (DSPC and SOPC) adsorbed on a hydrosol substrate on the concentration of NaOH in a solution of 5-nm silica particles has been studied by X-ray reflectrometry with the use of synchrotron radiation. Profiles of the electron density (polarizability) have been reconstructed from the experimental data within a model-independent approach. According to these profiles, the thickness of the lipid film can vary from a monolayer ($\sim$35 Å) to several bilayers ($\sim$450 Å). At the volume concentration of NaOH of $\sim$0.5 mol/L, the film on the hydrosol surface is a macroscopically flat phospholipid membrane (bilayer) with a thickness of $\sim$60 Å and with areas of (45 $\pm$ 2) and (49 $\pm$ 3) Å$^2$ per DSPC and SOPC molecule, respectively.