Arrangements of cationic starch of varying hydrophobicity on hydrophilic and hydrophobic surfaces.

Arrangements of cationic starches hydrophobized by acetylation (CS-acet) deposited from aqueous electrolyte solutions onto hydrophilized and hydrophobized silica surfaces were investigated by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and contact angle measurements. The influence of electrolyte composition, acetylation degree of cationic starch (DS(ACET)), and deposition method was examined. On a hydrophobic substrate, CS-acet formed an open film with structure strongly dependent on DS(ACET) and electrolyte composition of the solution. On a hydrophilic substrate, acetylation increased the hydrophobicity of the film when the starch was deposited by adsorbing. When deposition was made by spin coating, i.e., the CS-acet was forced onto the substrate, the hydrophobic tuning by acetylation was lost. The films deposited by spin coating were thicker and considerably rougher than those deposited by adsorbing.