Surface engineering of polymeric substrates using plasma technique and applications

• Main Author: Sun, Ye
• Other Authors: Chen Zhong
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Materials::Functional materials; Engineering::Materials::Plasma treatment
• Online Access: https://hdl.handle.net/10356/159090
• Institution: Nanyang Technological University

Superhydrophobic/superhydrophilic surface functionalization has been drawing much attention recently especially on polymeric materials. Polymers enjoy certain unique advantages such as light weight, low cost, and good flexibility, making them a favorable choice for a wide range of industrial applications. On the other hand, the surface properties of polymers may not be suitable for some specific applications, especially when extreme wetting states (e.g., superhydrophilic, superhydrophobic) are required. Therefore, it is necessary to modify the inert polymer surface without affecting the properties of the bulk to meet the performance requirements of different applications. Despite the fact that many methodologies have been explored to modify the surface to be superhydrophobic or superhydrophilic, many of them are not suitable for heat sensitive polymer materials. Additionally, the mechanical durability of modified surface is still a main challenge faced by many practical applications. Plasma processing is one of the most efficient ways to alter the surface feature as well as the surface chemistry at low temperatures. Although plasma process has been developed for a long time, little has been reported to modify the surface in a single process. In the thesis work, we will further develop the process to enhance functionality, durability as well as the reliability of the modified surface. Therefore, the aim of this research is to functionalize polymer surface for different application like oil-water separation, anti-fogging and anti-fingerprint via plasma surface modification and coating. The first result presented in this thesis shows a facile and chemical-free hydrogen plasma process, which can transform a superhydrophilic polyester fabric surface to superhydrophobic in treatment time of 4 min. The as-prepared superhydrophobic polyester has high efficiency in oil-water separation. Such strategy of preparing superhydrophobic polyester provides a pathway towards on-demand practical application such as treatment of oil contaminant. The second part of the result describes a designed and optimized process for coating polymeric materials with anti-fogging property. Pulse laser deposition of silica nanoparticles film created surface roughness and the surface chemical state to realize the necessary superhydrophilicity. With the aid of oxygen plasma surface treatment prior to deposition, coating exhibited excellent mechanical robustness and durability in terms of coating adhesion and abrasion resistance. Based on this finding, we continued to explore the possibility of constructing surface with other possible functional properties like self-cleaning and anti-fingerprint. By depositing titanium oxide nanoparticles on top of silica films, we not only retained the superhydrophilicity but also observed photocatalytic capability to remove organic residues on surface upon UV irradiation. Lastly, superhydrophilic silica nanoparticles films with abundant hydroxyl group on surface provided bonding sites of low surface energy fluorinated compounds. Rapid dip-coating of silica -coated substrates in fluorinated compounds functionalized the surface to be superhydrophobic and highly oleophobic with self-cleaning and anti-fingerprint properties. In summary, this research contributes to the development and optimization of the process of modifying polymeric materials surface with desire functional properties while demonstrating great mechanical robustness and durability.