Plasma functional polymerization of dopamine using atmospheric pressure plasma and a dopamine solution mist

Abstract

By using DBD-type atmospheric pressure plasmas and a dopamine solution mist formed by a piezoelectric module, the possibility of depositing functional polymer films showing the physical and chemical characteristics of polydopamine without breaking the functional group of the dopamine has been investigated for different plasma voltages. The higher DBD voltages up to 3.0 kV decreased the functional groups such as catechol and amine (N/C ratio) relative to dopamine in the deposited polymer by increasing the dissociation of dopamine into atoms and small molecules due to higher electron energies. In contrast, the lower DBD voltages up to 1.5 kV increased the functional group and N/C ratio of dopamine in the deposited polymer by keeping the molecular structures of the dopamine due to lower electron energies. Therefore, the polymer deposited at the lower DBD voltages showed lower contact angles and higher metal absorption properties which are some of the surface modification characteristics of polydopamine. When the metal absorption properties of the polydopamine-like film deposited using the atmospheric pressure plasma of a low DBD voltage with a dopamine solution mist were compared with other metal absorbers for Cu, As, and Cr, the polydopamine-like film exhibited superior metal absorption properties. It is believed that this atmospheric pressure plasma process can be also applied to the plasma polymerization of other monomers without breaking the functional groups of the monomers.

Fig. 1. Schematic drawing of the polydopamine-like coating module composed of a plasma module and a gas mixture module. (a) DBD-type atmospheric pressure plasma module, (b) dopamine solution gas mixture module, (c) cross section of the gas mixture module.

Fig. 2. Process sequence for polydopamine-like polymer thin film coating.

Fig. 3. SEM images before and after the polydopamine-like polymer coating for different DBD power voltages. (a) As-is (silicon wafer), (b) 1.5 kV, (c) 2.0 kV, (d) 2.5 kV, and (e) 3.0 kV of DBD voltages.

Fig. 4. XPS nitrogen (N1s) peak intensity and the ratio of N/C measured on the silicon substrate before and after deposition of polydopamine-like film as a function of DBD voltage for 60 s.

Fig. 5. FT-IR absorption peak intensity of polydopamine-like films deposited at different DBD voltages. (a) 1.5 kV, (b) 2.0 kV, (c) 2.5 kV, and (d) 3.0 kV.

Fig. 6. Water contact angles on the silicon substrates measured at different DBD voltages for the deposition of polydopamine-like polymer films. In addition to the gas mixture condition for the deposition of polydopamine-like thin films which is composed of He/dopamine mist (H₂O + dopamine), the gas conditions of He only and He/H₂O mist without dopamine were also investigated.

Fig. 7. SEM images of polydopamine-like films deposited at different DBD voltages after absorption of silver by exposing to 0.01 M silver nitrate solution for 6 h. (a) 1.5 kV, (b) 2.0 kV, (c) 2.5 kV, and (d) 3.0 kV.

Fig. 8. SEM images of polydopamine-like films deposited at different DBD voltages after absorption of silver by exposing to 0.01 M chromium chloride solution for 6 h. (a) 1.5 kV, (b) 2.0 kV, (c) 2.5 kV, and (d) 3.0 kV.

Fig. 9. XPS narrow scan peak intensities of (a) Ag and (b) Cr on the polydopamine-like polymer deposited at different DBD voltages after exposure to 0.01 M silver nitrate solution and 0.01 chromium chloride solution for 6 h.

Fig. 10. Metal absorption weight/unit area for different metal absorption materials. As the metal absorption materials, commercial materials such as ion exchange resin bead materials (IR120 and HCR-S) and one arsenic/metal removal filter bead material (AS600) in addition to the silicon wafer deposited with the polydopamine-like thin film at 1.5 kV for 60 s were included. The materials with the same surface area of 100 mm² were immersed for 24 h in the three different metal containing solutions of copper nitrate trihydrate, arsenic standard solution, and chromium chloride hexahydrate. After the immersion of materials for 24 h, the remaining metal content was measured by ICP-OES for the calculation of absorption weight/unit area.

Fig. 11. Polydopamine-like thin film thickness measured as a function of deposition time at the DBD voltage of 1.5 kV.

Fig. 12. Surface roughness of the polydopamine-like thin film deposited on silicon wafers measured as a function of deposition time. (a) 15 s, (b) 30 s, (c) 45 s, and (d) 60 s at the DBD voltage of 1.5 kV.