Study of adsorption behaviors on a SiO2 surface using alkyl cationic modified starches

Quartz crystal microbalance with dissipation monitoring (QCM-D) was performed in order to study the adsorption behavior of monoelectrolytes (cationic surfactants: C12–16 trimethyl ammonium bromide) and polyelectrolytes (cationic starches and cationic alkyl substituted starches). An adsorption step using surfactant or polymer solutions and a desorption step of rinsing with distilled water were adopted in order to observe the adsorption behavior. The adsorbed amount of all cationic starches increased compared with that of the cationic surfactants, and the adsorption gap between the adsorption and desorption processes was remarkably small. In addition, a tendency for increased rigidity after desorption was observed. In particular, the cationic alkyl (C12–18) substituted starches had long alkyl chains as well as polymer backbones. In the results, the adsorbed layer of the cationic alkyl substituted starches increased more than the general cationic starches and exhibited more rigid properties. These results were attributed to the hydrophobic interactions among polymers originating from long alkyl chain substitutions.