Plasma treatment timeliness

Materials treated with plasma can introduce polar functional groups on the surface, improving the wettability and adhesion of hydrophobic polymer materials to water. However, over time, the number of these functional groups gradually decreases, and the oxygen content on the material surface decreases. The improved hydrophilic properties on the surface return to the hydrophobic state before treatment. This phenomenon is commonly referred to as the time-dependent effect of low-temperature plasma treatment on the surface properties of materials.

Characterization of timeliness

Due to the fact that plasma only acts on the surface of the material, some physical and chemical changes that occur in the material after treatment mainly occur in this layer. Therefore, the characterization of aging mainly uses some physical and chemical analysis methods about the material surface. Mainly includes testing of material contact angle.

Reasons for Timeliness

The aging mechanism of plasma treatment is complex and there is no unified explanation. Currently, there are two recognized models. One is the polar group flipping model: after plasma treatment, a large number of active groups are generated on the surface of the material, but with time migration, the groups tend to move towards the interior of the material, making the overall energy of the material reach equilibrium and stability; The second is to clean the model: it is believed that after plasma treatment, the large molecular chains on the surface of the material break and form many small molecular substances, but the small molecular substances are easily oxidized over time, and the modification effect gradually disappears.

Factors affecting timeliness

(1) Types and characteristics of polymer materials:

The crystallinity of polymer materials has a significant impact on the timeliness of plasma treatment. For high crystallinity polymer materials, due to the tightly ordered arrangement of molecules in the crystalline region and the small intermolecular distance, the flipping of surface polar groups and the movement of chain segments after plasma treatment require overcoming significant resistance, resulting in a smaller degree of attenuation of surface polar groups. For polymer materials with low crystallinity, the internal amorphous region has a loose molecular structure, large intermolecular distances, and easy movement of molecular segments, resulting in significant attenuation.

(2) Plasma atmosphere and processing parameters:

Mainly including plasma atmosphere, plasma treatment power, plasma treatment time, and substrate temperature of the processed material.

(3) Storage environment after plasma treatment of materials:

The storage environment of processed materials can also have an impact on timeliness, including two factors: storage medium and temperature. In the same storage medium, the higher the ambient temperature, the more significant the timeliness. This is because molecular chains can gain more energy, the movement of molecular segments is strengthened, and the flipping of surface polar groups is also more rapid. But if the storage environment is hydrophilic, even at higher temperatures, it can suppress the loss of polar groups on the surface of polymer materials. Hydrophilic storage media facilitate the retention of polar groups generated on the surface of materials; On the contrary, a hydrophobic storage environment promotes the reversal of polar groups on the surface of the material into the interior of the matrix.

The issue of the timeliness of plasma treatment effect is common. As the storage time prolongs, the surface of the treated polymer material will gradually restore its hydrophobicity. Using it as soon as possible is an effective solution to avoid the timeliness of plasma treatment.