Nch vs1 w

AFM imaging was performed in atomic force microscopy tapping mode with a Veeco multimode scanning probe microscope (Bruker, USA). The images were scanned using silicon cantilevers (NCH-VS1-W, Nanoworld, Switzerland) with a resonance frequency of 320 kHz and a force constant of 42 N·m⁻¹. All images were processed using Nanoscope software package (V7.30r1sr3, Veeco).
The roughness layer thickness RLT^AFM is evaluated from the topography images measured by AFM, compare Figure 2. The roughness layer is the region of the cellulose film where both, material and ambient medium (water or air) are found, i.e., the region containing the boundary between cellulose film and surrounding. The thickness of this region depends on the roughness of the film. We have defined the roughness layer as the z-directional layer containing 95% of the surface roughness. For calculation, the histogram of the topography distribution is evaluated. From each edge of the histogram, 2.5% of the topography values are clipped off, the topography range comprising the remaining 95% of height values is defined as the roughness layer thickness. We are not using 100% of the values because the topography distribution is close to normally distributed which means there are always some far outliers which would bloat the roughness layer beyond the true surface interaction range.

Surface morphology and roughness of the films on Si, glass, Cu, Ni and Al were determined on a Veeco Multimode Quadrax MM scanning probe microscope (Bruker, Billerica, MA, USA) using Si cantilevers (NCH-VS1-W from NanoWorld AG, Neuchatel, Switzerland) with a resonance frequency of 320 kHz and a force constant of 42 N·m⁻¹. On the polymer substrates, the films were analyzed using a FastScanBio AFM using a FastScan-A cantilever (both from Bruker NANO) with typical resonance frequencies and force constants around 1.4 MHz and 18 N·m⁻¹, respectively. All samples were analyzed in tapping mode in an ambient atmosphere at room temperature at the lowest possible force load and scan rates were adapted to obtain reliable surface data. Root mean square (RMS; R_q) roughness calculation and image processing was performed with the Nanoscope software (V7.30r1sr3, Veeco, Plainview, NY, USA).