Abstract: A surface modified substrate, wherein the substrate carries a complex adsorbed thereto, which complex is of a polymeric cationic surfactant that contains primary amino nitrogens as well as secondary and/or tertiary amino nitrogens, and a dialdehyde that has 1-4 carbon atoms between the two aldehyde groups. To said complex there may additionally be bonded an anionic compound and optionally alternatingly additional cationic and anionic compounds. The modification primarily means that positive or negative charges can be imparted to the original substrate. Secondly, however, the point may be to utilize reactive groups in bonded cationic or anionic compounds.