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 (∼ 35Å) to several bilayers (∼ 450Å). At the volume concentration of NaOH of ∼ 0.5 mol/L, the film on the hydrosol surface is a macroscopically flat phospholipid membrane (bilayer) with a thickness of ∼ 60Å and with areas of 45 ± 2 and 49 ± 3Å 2 per DSPC and SOPC molecule, respectively. * tikhonov@kapitza.ras.ru
The structure of the transient layer at the interface between air and the aqueous solution of silica nanoparticles with the size distribution of particles that has been determined from small-angle scattering has been studied by the X-ray reflectometry method. The reconstructed depth profile of the polarizability of the substance indicates the presence of a structure consisting of several layers of nanoparticles with the thickness that is more than twice as large as the thickness of the previously described structure. The adsorption of 1,2-distearoyl-sn-glycero-3-phosphocholine molecules at the hydrosol/air interface is accompanied by the condensation of anion silica nanoparticles at the interface. This phenomenon can be qualitatively explained by the formation of the positive surface potential due to the penetration and accumulation of Na + cations in the phospholipid membrane.
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