Hydrophilic Treatment

Good wettability on the surface is a prerequisite for ensuring adhesion with the bonding partner during painting, bonding, printing, or bonding. Not only do pollutants containing oil and grease hinder wetting, but also the clean surfaces of many materials cannot be fully wetted by various liquids, adhesives, and pigments. Liquid droplets cannot adhere to the surface even after solidification or drying treatment.

The reason is that the surface energy of the substrate is relatively low. Materials with lower surface energy can wet materials with higher surface energy, but not vice versa. The surface energy of the applied liquid, also known as surface tension in the liquid, must be lower than the surface energy of the substrate in any case.

A very important application of plasma technology is hydrophilic treatment. This process is used to modify the surface to make it highly attractive to water. This is opposite to hydrophobic treatment that makes the surface repel water. Some materials naturally have hydrophobicity, which means that water condenses into water droplets and does not spread evenly to the surface. If you want to paint or adhere something to the surface, this may be a problem as paint and glue cannot adhere well to the surface. When the surface undergoes hydrophilic treatment, it increases the surface energy of the object. When an object has high surface energy, it has high adhesion ability.

Why does plasma cleaning make the material surface hydrophilic

Plasma, also known as the fourth state of matter, is the ionization of gas in a high-voltage electric field, producing charged positive and negative particles, including aggregates composed of positive ions, negative ions, electrons, free radicals, and various active groups. The reason why plasma cleaning can make the material surface hydrophilic is because it utilizes the energy particles and active groups in the plasma to interact with the material surface, thereby achieving the goal of changing the surface composition.

Surface hydrophilic functional groups increase

The smaller the surface contact angle of an object, the better its wettability. Wetting is a necessary condition for adhesion. After plasma treatment of the material surface, the introduction of a large number of oxygen-containing functional groups significantly improves the surface wettability, which is beneficial for enhancing surface adhesion. Normally, after being treated with gas plasma such as Ar, 02, N2, etc., polymer materials will introduce functional groups such as - C00H, - C==0, - NH2, etc. on the surface to increase surface hydrophilicity.

Changes in surface roughness

After plasma treatment, the surface roughness of the material increases to varying degrees due to the etching effect of dry plasma on the material surface, which in turn affects the adsorption of liquid on the surface and ultimately changes the surface wettability.

How Hydrophilic Treatment Works

Naen can use its low-pressure plasma systems to perform  hydrophilic treatments on objects of various sizes and shapes. The target object is placed within an airtight chamber. Next the pressure of the chamber is lowered by using a vacuum to remove all of the air. Then, to begin the hydrophilic treatment, a precursor gas is inserted into the chamber where the combination of energy and a low-pressure causes the gas to ionize and become plasma. The excited plasma ions collide with the surface, microscopically changing the geometry of the surface. Specifically, during a  hydrophilic treatment, the surface undergoes oxidation and the bombarding plasma ions form hydroxyl groups on the surface. These hydroxyl groups are polar, and since water is polar, it is attracted to them. Ultimately, this is what enhances the surface’s wettability and adhesion.