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This thesis focuses on the combination of bioinspired designs with opposite interfacial properties for the fabrication of self-cleaning liquid-infused surfaces via mussel-inspired chemistry. On the one side, the adhesive chemistry inspired by the mussel-foot protein serves as a toolbox for surface anchoring. This mussel-inspired chemistry is based on the adhesive and anchoring capability of catechol and catecholamine groups, which can be incorporated either as end-groups in molecules, as side chains, or in the backbone in polymers. These molecular or polymeric thin film layers can be modified by pre-functionalization, co-deposition, or post-modification of functional groups to impart self-cleaning, mechanical stability, and liquid and solid repellency. On the other hand, the self-cleaning liquid-infused surfaces inspired by the pitcher plant’s peristome impart the liquid and solid repellent properties. The aim of this thesis is twofold. On the one side, the versatility and universality of the adhesive properties of the catechol-based chemistry serve as surface anchoring and functionalizing of various material types, like polymer, ceramic, metal, and glass. On the other hand, the fabrication process of liquid-infused surface (LIS) was meant to be optimized to achieve an experimentally facile, scalable coating process without specialized equipment. An additional aspect achieved in the present thesis was matching the LIS fabrication to the required and desired application. This matching was achieved by the versatility of the reactive sites on catecholamines. These reactive sites provide another toolbox to tailor the liquid-infused surfaces' fabrication by using various oils. The three-step method was investigated in reference to the surface wetting and chemistry in order to understand the influence of the individual process steps. Here, a thin film of crosslinked PDA polymer was applied by oxidative polymerization of dopamine, leading to polydopamine (PDA). The thin-film polymer coating was then functionalized with monoaminopropyl-poly(dimethyldisiloxane) (MAP-PDMS). Both the polymer coating and functionalization were investigated by wetting and elemental analysis. Eventually, the functionalized PDA surface was infused with silicone oil as a lubricant. The slippery nature of the surface was proofed by contact angle hysteresis (CAH) of water. The know-how collected in the three-step process was then applied to design one-step processes. The challenge was to dissolve a polar molecule like dopamine, which is soluble only in water, methanol, ethanol, and aprotic polar solvents, and the nonpolar macromolecules like PDMS and MAP-PDMS. This challenge was overcome by using a mixture of methanol and tetrahydrofuran. As a paint base, we used a solution of dopamine, triethylamine (TEA), MAP-PDMS, and silicone oil. The solution could be applied directly or left to react for 96 h until a dark pre-reacted dispersion is formed and then applied for LIS fabrication. We fabricated LIS both with the unreacted solution and the pre-reacted dispersion via both dip and spray coating. The presence and its physical and chemical nature of a thin polymer film were confirmed by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and wetting measurements. These LISs were then applied to repel complex and non-Newtonian substances like honey and ketchup. Furthermore, we showed the possibility to coat complex geometries like cotton textiles and a wooden honey spoon with a high specific surface area. With the design of one-step processes, we fulfill one of the two aims of the present thesis. The LIS fabrication process was further optimized by removing the organic solvents, which are potentially harmful to health and the environment. We achieved the organic solvent removal by developing an in-situ self-functionalizing lubricant. Briefly, the lubricant contains a reactive moiety, which is able to adjust and tailor both the surface chemistry and energy of the underlying substrate layer to the applied lubricant. We investigated the temporal progression of the surface functionalization both in-situ with quartz crystal microbalance and ex-situ by ellipsometry measurements after each surface modification step. We showed the versatility and universality of the substrate material types as well as the lubricant types. This versatility would allow adjusting the LIS fabrication to the desired substrate and to the lubricant system like silicone oil, hydrocarbons, natural fatty acids, and ionic liquids. The LIS fabrication, both by one-step and two-step process, was applied to an actual product, protective shoe soles, in order to repel cement after one day of drying in air at room temperature. The one-step spray coating processes and the two-step dip-coating process showed promising results by decreasing the cement adhesion to both glass and actual shoes soles. Another concept based on pre-functionalized catechol-containing molecules was applied to fabricate LIS. Here, one side of the molecule presents the catechol surface anchoring group and the other side, the surface functional group. We showed by nuclear magnetic resonance (NMR), and Fourier transform infrared spectroscopy (FTIR) the successful synthesis of the catechol-containing and dodecaneamine molecule. By applying a mixture of the catechol-containing molecule with dodecane as a lubricant, we fabricated a LIS. Eventually, we applied active ester chemistry with poly(pentafluorophenolacrylate) (pPFPA) to have maximum flexibility to functionalize the side chains with either the catecholamine anchoring groups or an alkyl- or alkoxysiloxaneamines for lubricant affinity. Firstly, we showed the successful synthesis of the PFPA monomer and the pPFPA polymer by NMR. The functionalization with dodecaneamine, MAP-PDMS, or dopamine was confirmed both by NMR and FTIR. The surface functionalization with the side-chain catechol-containing polymer was confirmed on glass substrates by XPS. |
