Zeta potential of the polymer electrolyte laminated film

The glass surface, which is mainly composed of silica, has a negative charge except in the strong acid region. It is known that when it is adsorbed with a cationic polyelectrolyte (polyethyleneimine, poly-L-lysine, etc.) having a different charge from its surface, a polymer adsorption layer having an opposite charge against the original surface is formed. Furthermore, when an anionic polyelectrolyte (sodium polystyrene sulfonate, sodium polyacrylate, etc.) is adsorbed on it, an adsorption layer with an opposite charge against the first one is formed. By using such a method, it is possible to stack polymer adsorption layers by alternately adsorbing two types of polyelectrolytes with different charges.

Until now, as a method for producing an organic thin film by the lamination method, the Langmuir-Blojet (LB) film method for forming a thin film by laminating a long-chain fatty acid formed at the air-water interface on a substrate is well known. On the other hand, the thin film obtained by laminating polymer electrolytes does not have molecular orientation, but it can withstand practical use because it is firmly bonded by the entanglement effect peculiar to polymers and strong electrostatic attraction. It has the advantage of having a high molecular weight. Another feature is that molecules and colloidal particles that selectively bind to the functional groups of the polyelectrolyte can be embedded in the laminated membrane after lamination. Due to these advantages, it is expected that it can be used in a wide range of industrial fields such as pharmaceuticals, pesticides, foods, and cosmetics, rather than LB membranes.
Experiments on the fabrication of laminated films of polymer electrolytes are often performed on latex and inorganic particles that can be used for colloidal science experimental methods such as zeta potential measurement and particle size measurement for analysis of the lamination process.¹⁾  However, in practice, it is ideal to try on a smooth substrate with a fixed area.

Therefore, in this study, polymer electrolytes with different charges were alternately adsorbed on a slide glass, and its zeta potential was measured by using the flat surface sample measurement method to confirm if the polyelectrolytes can be adsorbed alternately on the glass similar to its adsorption on particles and the adsorption conditions were examined.