PMMA oxygen plasma hydrophilic treatment

Polymethyl methacrylate (PMMA) is a transparent, colorless, weather-resistant polymer material. In the visible light band, the transmittance of PMMA is as high as 92%. It is widely used in transparent plastic plates, optical fibers, optical devices and other fields.

Due to the low surface energy and chemical inertness of PMMA surface, the material often exhibits surface inertness and hydrophobicity, making it difficult to wet and bond. Therefore, PMMA needs to be subjected to plasma surface treatment to change its surface chemical composition, increase its surface energy, and improve its surface wettability.

Plasma refers to an ionized gaseous substance composed of electrons and ions generated by the ionization of some atoms. It is the fourth state of matter in addition to solid, liquid and gas. Plasma treatment technology refers to the use of active particles in low-temperature plasma to bombard the surface of polymer materials, so that the chemical bonds of the molecules on the surface of the material are broken and combined with nitrogen, oxygen and other free radicals in the plasma to form a large number of hydrophilic groups such as carboxyl and hydroxyl on the surface of the material, which significantly improves the hydrophilicity and biocompatibility of the material surface.

Oxygen plasma treatment of PMMA

The energy generated by oxygen plasma particles can cause various chemical bonds (C-H; C-N; C=O; C-C; C=C; C≡C) in the polymer to break or recombine, resulting in the degradation of macromolecules. The surface of the PMMA material and oxygen react under the action of plasma to form a C-O structure. Oxygen is a reactive plasma that participates in surface chemical reactions, introduces oxygen-containing active groups on the surface of the PMMA material, and generates a large number of free radicals, as shown in Figure 1.

Figure 1 Schematic diagram of PMMA oxygen plasma treatment

Comparison of water drop angle before and after PMMA oxygen plasma treatment

Liquid forms droplets on the solid surface. When the droplets reach equilibrium, the angle between the gas-liquid interface and the solid-liquid interface at the junction of the gas, liquid and solid phases is called the contact angle, represented by θ. The smaller the contact angle, the better the wettability. Wetting is a necessary condition for adhesion. The water drop angle of the PMMA material surface after plasma treatment is shown in Figure 2. Due to the presence of hydrophilic oxygen-containing groups, the wettability of the PMMA material surface is significantly improved, which is conducive to subsequent bonding, bonding and other processes.

Figure 2: Before plasma treatment on the left and after plasma treatment on the right

PMMA plasma surface hydrophilic modification technology is a dry chemical modification technology that does not require water during the treatment process and only involves gas-solid phases. When the reaction occurs, the particles bombard the matrix, which can effectively change the surface free energy, wettability and other properties of the material. The plasma treatment process occurs on the surface of the material, with a depth of several to several hundred nanometers, so it will not change the properties of the material matrix; the gases used for modification are generally oxygen, argon, etc., and no harmful gases will be produced.