Facile and Fast Fabrication of Functional Thin Films Via Polyelectrolyte Layer-by-layer Assembly

Download or read book Facile and Fast Fabrication of Functional Thin Films Via Polyelectrolyte Layer-by-layer Assembly written by Szu-Hao Cho and published by . This book was released on 2020 with total page 185 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fabrication of functional thin films has always been of great importance to the scientists and engineers because of their versatile applications in different fields such as biomedical and coating industries. Polyelectrolyte layer-by-layer (LbL) assembly, due to its simple fabrication process, flexibility to be applicable to different kinds of substrate with almost any geometry and topography, and the ability to precisely control the thickness and composition of the constructed multilayers, has been extensively used to build up thin films over the last decade. However, this process is time-consuming and the functionalization of LbL films always involves either multiple steps or harsh conditions, which make this technique impractical to produce functional thin films from the industrial point of view. In this dissertation, three different approaches are proposed to overcome these difficulties of LbL assembly and therefore enable us to develop LbL functional thin films more efficiently. The first approach is to incorporate rapid thiol-ene click reaction into self-healing polyelectrolyte multilayers (PEMs) for its post-fabrication functionalization via LbL assembly of branched polyethylenimine and allyl-modified poly(acrylic acid). By applying the thiol-ene reaction to the pendant ene functionality we demonstrated that different functional groups can be easily introduced to the LbL films to tailor the surface wettability. Photoinduced thiol-ene reaction also allows us to make wettability and fluorescence patterns on the surface. Moreover, the fabricated PEMs after surface functionalization still possess remarkable self-repairing ability against damage, which substantially prolongs their lifetime. Although the recurrent scratch damage results in the gradual loss of the surface property, the unused ene functionalities buried inside the PEMs can be functionalized again to retain the desired surface property and therefore, brings up the concept of refunctionalizable surfaces. The second approach is to perform LbL assembly of BPEI and Nafion, a perfluorinated polyelectrolyte, in methanol and a hierarchically rough and superhydrophobic surface is obtained directly with only 3 bilayers without further modification. The surface properties are shown to highly depend on the LBL assembly parameters, including deposition cycles, dipping time, rinsing time, and drying time between baths. BPEI/Nafion multilayers obtained with this method is then infused with Krytox 100 lubricant to facilely fabricate slippery liquid-infused porous surfaces (SLIPS), which show excellent omniphobic, antifouling, self-cleaning, flexible, and optical properties. The results in this study not only simplifies the fabrication of SLIPS, but also provides great insight for making LBL films with specific morphologies.In the last approach we demonstrate we can prepare patterned slippery surfaces without any complex surface chemical modification and involve only 3 steps, LbL assembly, hydrophilic polymer patching, and lubrication. A superhydrophobic base film is produced via LbL assembly of BPEI and Nafion in methanol, as demonstrated in the second approach. After that, concentrated BPEI patterning solution is applied to the surface to create the hydrophilic regions. Because these hydrophilic domains have a stronger affinity to the aqueous media than the lubricant, a slippery surface with the hydrophilic pattern which constrains the impinging liquid motion can be easily obtained after infiltrating the lubricant to the surface. This approach not only offers an efficient way to prepare the patterned slippery surfaces but also provides the versatility for different applications such as transparent surface patterning and liquid manipulation. Moreover, the flexibility of incorporating a solvatochromic dye into the patterning solution has opened a new area for patterning slippery surfaces in anti-counterfeiting technology.