Layer-by-layer assembly of lignosulfonates for hydrophilic surface modification

Lignosulfonates (LS) were used to modify the surface of a mica substrate using Cu²⁺ as the binding agent through layer-by-layer (LbL) self-assembly. The average thickness and roughness of the self-assembled multilayer of LS–Cu²⁺ complexes increased with the number of layers as revealed by atomic force microscopy. The hydrophilicity of the modified surface decreased with the increase in the number of layers. The contact angle was increased from 6.5° to 86° after the mica surface was coated with 18 layers of LS–Cu²⁺ complexes. This suggests that surface hydrophilicity can be modified in a controllable manner via LbL assembly of lignosulfonates.