Figure 2.

(a) Infrared transmission spectroscopy studies of the thick membrane samples and silicon substrate. Arrows point to the specific vibration observed in PDA. The inset shows the inspected regions. (b) Atomic force micrographs collected from the thin sample on silicon. The top panel shows a large-scale image of one of the boundary sections of the PDA film. Dashed square and black arrows show a section in which the presence of a double layer is observed. The middle panel shows a zoomed-in micrograph of this section and the presence of three regions, marked as L1, L2, and silicon. The dashed arrow shows the profile of the image, which is represented in the bottom panel of the same image. (c) A representative load vs displacement curve obtained from the thick sample. The inset shows the box distribution of the E and H for the sample.