Plasma Surface Modification for Corrosion Protection and Electrochemical Glucose Sensing
Student thesis: Doctoral Thesis
Plasma is a high activated state of matter. Plasmas contain ionized species able to easily initiate chemical and physical reactions at the surface of other materials. Accordingly, plasma techniques have been developed as surface modification methods. By surface modification of materials, new surface properties can be achieved. In this thesis, various plasma surface modification techniques, such as plasma ion immersion implantation (PIII), plasma deposition, ion implantation and magnetron sputtering, are applied to the surface modification of different materials. The application study in this thesis mainly focuses on two subjects: corrosion protection and electrochemical glucose sensing.
The first chapter gives an overview of plasma surface modification, fundamentals of corrosion science, and electrochemical glucose sensing.
In the second chapter, cerium ion implantation is conducted to modify the surface properties of pure Mg and the effects of cerium ion implantation on the corrosion behavior of Mg are evaluated in different biological medias. Electrochemical polarization and immersion tests show that the corrosion resistance of the Mg samples is improved in artificial hand sweat, Ringer's solution, and complete cell culture medium (cDMEM) after Ce ion implantation with the most significant improvement observed from cDMEM. The retardation effect is attributed to the formation of a robust cerium-rich oxide layer formed by energetic ion bombardment and implantation.
In the third chapter, plasma ion immersion implantation and deposition (PIII&D) is conducted to deposit a diamond-like carbon (DLC) film on the NdFeB permanent magnet. The as-deposited DLC film is characterized by atomic force microscopy, scanning electron microscopy, Raman scattering, and mechanical tests. Electrochemical and immersion tests conducted for different time durations show that the corrosion resistance in 3.5% NaCl and 5 mM H2SO4 is improved by the DLC coating and corrosion tests also reveal enhanced corrosion resistance in both media. The corrosion mechanism of both the untreated and DLC-coated NdFeB is proposed and discussed.
In the fourth chapter, magnetron sputtering is conducted with hydrothermal treatment to modify the sample surface of AZ80 alloy. A super-hydrophobic surface is proposed to be fabricated on AZ80 alloy inspired by the lotus leaves effect in nature. Firstly, hydrothermal treatment is conducted to form a self-layered coating that consists of an inner compact layer and a top Mg-Al layered double hydroxide (LDH) microsheet-based layer. This coating has excellent corrosion resistance in saline solutions whereas can’t resist the attack from sulfuric acid solutions. Ensuring magnetron sputtering with polytetrafluoroethylene (PTFE) as target materials produces a layer of polymeric film on the microsheets, inducing the formation of a water-repellent surface on magnesium alloy. Compared to the surface modified by hydrothermal method, the super-hydrophobic surface can render a better corrosion protection in H2SO4 solutions due to the existence of the trapped air pockets in the microsheet array. The dual process offers a promising means to mitigate the corrosion of magnesium alloy in acid solutions.
In the fifth chapter, we proposed a new strategy to utilize ion implantation as an inductive process, which can facilitate the predesigned surface passivation of Mg by hydrothermal treatment. Ti-ion implantation and hydrothermal treatment are conducted sequentially to modify pure magnesium. With only hydrothermal treatment, a nanocrystal-composed Mg(OH)2 film is formed. However, with ion-implantation-induced hydrothermal treatment, a double layer film is formed, with an upper layer of Mg(OH)2 nanoplates and an inner layer composed of Mg(OH)2 nanocrystal. The mechanism of hydrothermal treatment is discussed. The hydrothermal-treated samples show improved corrosion resistance and the ion-implantation-induced hydrothermal treated sample shows enhanced cytocompatibility.
In the sixth chapter, nickel (Ni) ion plasma is utilized to modify graphene and a Ni-graphene based glucose sensor is fabricated on a glassy carbon (GC) electrode. The Ni plasma-modified graphene (G-Ni), which has structural integrity and good conductivity after the plasma treatment, shows excellent glucose sensing ability as confirmed by electrochemical assessment of the GC-G-Ni electrode. The GC-G-Ni sensor exhibits a high glucose sensitivity of 2213 μA mM−1 cm−2, low detection limit of 1 μM, short response time of less than 1 s, good selectivity, long-term stability, and reproducibility. The fabrication method and strategy are promising to large-scale production of electrochemical biosensors based on transition elements.