|Title:||Synthesis, characterization, and applications of smart and biomimetic textile materials for manipulation of liquid|
|Advisors:||Xin, John H. (ITC)|
Fei, Bin (ITC)
|Subject:||Hong Kong Polytechnic University -- Dissertations|
|Department:||Institute of Textiles and Clothing|
|Pages:||xvi, 198 pages : color illustrations|
|Abstract:||A series of textile based smart materials have been designed and fabricated in this thesis integrating a variety of bio-inspired concepts to manipulate different types of liquids on solid surface. The stimuli responsiveness endows the biomimetic materials or surfaces with better flexibility, adaptability, and controllability to achieve various on-demand applications. According to different manipulation mechanism towards liquid behaviors, this study is divided into four research systems: (i) manipulation of liquid wetting behavior between hydrophilic and hydrophobic states by a temperature-responsive nanofiber system and its application in smart separation of oil/water mixture at different temperature; (ii) manipulation of liquid wetting behavior between superhydrophilic and superhydrophobic states by a light/heat responsive nanofiber membrane and the application in reversible separation of oil/water mixtures; (iii) manipulation of the directional condensation and coalescence of water droplets on a superhydrophobic cotton fabric surface with light-induced superhydrophilic bumps and its application in water collection from fog; (iv) real-time manipulation of the coalescence and sliding of liquid droplets on a flexible slippery surface with tunable morphology along with external tensile stress and its practicability in wind-resistance water collection.|
The above division of this thesis is according to the evolving manipulation mechanism towards liquid behaviors from static to dynamic, and also from simple to complex. Specifically, the liquid wetting behavior is a basic property of a solid surface, and with simple and uniform modification of surface chemical composition or surface energy, a statically hydrophilic or hydrophobic surface can be obtained. By grafting stimuli-responsive polymer brushes with adjustable surface energy, a smart transition between wetting and non-wetting can be achieved. However, the single control of surface energy is not sufficient to fabricate surfaces with extreme wettability, such as superhydrophilicity and superhydrophobicity. A delicate construction of surface microstructure is also necessary to form hierarchical roughness. Therefore, stimuli-responsive change of surface energy accompanied by a highly roughened microstructure is required to design smart material with super-wetting/resistant surface. Further, dynamic manipulation of liquid behaviors such as directional condensation and coalescence requires higher level of material design. Driven force commonly generated from wettability gradient or shape gradient should be included to lead the mobility of liquid droplets. Meanwhile, the integral surface energy and roughness should still be well regulated to ensure the low friction during droplet movement. Thus, the more sophisticated design including both integral surface construction and detailed decoration with multiple ingredients make it possible to realize more complicated manipulation towards liquid behaviors. Finally, compared to those stimuli responding mechanism that needs long time exposure to certain stimuli or has slow response speed, a real-time stimulus response is considered to be of better controllability while giving rise to more sophistication towards material design. To achieve real-time manipulation of liquid behaviors such as coalescence and sliding, a material surface should show immediate change in surface property such as morphology, wettability, or friction along with external applied stimuli and should possess sufficient flexibility for both the substrate and modification agent, as well as the good coordination between each other. In this thesis, we conducted in depth study for various basic mechanisms of liquid manipulation learning from creatures in nature and summarized a variety of design concepts of biomimetic materials from literature. Following this, we creatively designed different kinds of stimuli-responsive materials and strategies to develop smart and biomimetic composite materials or surfaces aiming to improve their controllability and expand their applications. Besides, the incorporation of diverse textile substrates with appropriate properties makes such kind of materials more readily available and easier to be scaled up. This attempt may facilitate the interdisciplinary studies among traditional textile technology and new branches of science, and possibly promote their industrialization.
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