(a) Sample holder for neutron reflectometry experiments. The neutron beam passes through a thick silicon crystal and is reflected at the solid/liquid interface. Here, the supported asymmetric OM model, containing deuterated PL and hydrogenous rough LPS is surrounded by a buffer solution that can be easily exchanged through the cell inlets and outlets. (b) Data obtained from a typical NR experiment. The intensity of the specularly reflected neutron beam is measured as a function of Q, a combination of neutron wavelength and incident angle [53]. The asymmetric PL/LPS OM model is measured at three solution isotopic conditions (data points) which are simultaneously fitted (lines) to a common model that describes the interfacial bilayer structure shown in c. Curves are offset for clarity and the intensity is multiplied by Q⁴ to correct for the inherent decline in intensity with increasing angle. (c) structure of the deuterated PL (purple)/hydrogenous LPS (black) asymmetric bilayer described by the scattering length density (SLD) distribution of nuclei across the membrane profile. Note how SLD (in effect the neutron refractive index) of the acyl chains differs between natural LPS, deuterated lipids and different concentrations of D₂O. The corresponding structure of the interface is shown above the profile. b and c are reproduced from [26].