Quantitative analysis of atomic force microscopy topographs of biopolymer multilayers: Surface structure and polymer assembly modes

The morphology of polymer multilayer surfaces has been studied by quantitative analysis of atomic force microscopy (AFM) topographs. Multilayers were prepared for three different systems: chitosan–alginate, poly(L-lysine)-alginate and chitosan–scleraldehyde polymer pairs with up to 10 layer pairs. These utilized either an electrostatic dominated mechanism for the chitosan–alginate and poly(L-lysine)-alginate pairs, or covalent linkage for the chitosan–scleraldehyde pair. The surface structures were studied by evaluating the power spectral density (PSD) obtained from the height autocorrelation function calculated from the AFM topographs. By fitting the averaged PSD to the k-correlation model, information related to surface features such as pore size was extracted. Additionally, the dimensions of pronounced network strands were extracted from the peak at large spatial frequency observed for some of the multilayers. The analysis shows that quantitative information about properties of network like surfaces can be extracted, i.e. development of mean pore sizes of the multilayers prepared using stiff polymers and that such pore size can be tuned by choosing the components of the polymer pairs employed and/or the number of layer pairs.