Table 1. Simulation parameters for virtual NR experiments of the test system shown in Fig. 1 ▸ .

Where ranges are given in the first data column, parameters were systematically varied in the optimization. The nSLD of bulk Si is fixed at 2.07 × 10⁻⁶ Å⁻². When the structure was characterized using more than one solvent contrast, each additional measurement carried its own parameter for the solvent nSLD and scattering background.

Model parameter	Parameterized sample representation,	Fit boundaries, prior PDF limits
Thickness of interstitial water (Å)	20	±10
Thickness of porous layer (Å)	30	±10
SLD of porous layer (10−6 Å−2)	[−0.5, 6.5]	±1
Volume fraction of porous layer	0.95	±0.05
SLD of solvent, ρn (10−6 Å−2)	[−0.5, 6.5]	±0.5
Interfacial roughness (Å)	3	±2
Log10 of background†	−8	±1

^†A constant background is routinely fitted as a free parameter to each experimental NR curve, and the same procedure is adopted here. This accounts for insufficient background subtraction during data reduction and is typically 10% or less of the total background.