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Surface functionalization and surface patterning based on UV-induced dopamine polymerization and disulfide exchange strategies

Du, Xin

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Abstract

Surface functionalization methods are very important for modern science and technology in order to endow surfaces with various novel and unique properties. Examples include slippery property, antibacterial and antifouling properties, superhydrophobicity and superhydrophilicity, biocompativity and conductivity. As an important branch of surface functionalization, surface patterning has attracted a lot of attention. Patterned surfaces can find a wide range of applications in various fields such as microfluids, printing devices, sensors and diagnose devices to name a few. Photo-based surface functionalization is one of the most powerful surface modification and patterning methods due to its controllability both spatially and temporally. Different goals could be achieved by surface modification, for example, addition or remove of functionalities and formation of 3D morphologies. This thesis contains three parts, which deal with different topics related to surface functionalization. Part I demonstrates the method of UV control of dopamine (DA) polymerization and polydopamine (PD) deposition. PD coating is a recent surface modification strategy inspired by the adhesive performance of mussels. DA is able to self-polymerize in aqueous solutions under basic conditions. The adhesive nature of the resulting PD, allows it to attach to any immersed substrates forming a PD layer. Further functionality can be introduced using the reactivity of PD layer towards thiols, amines and metal ions. The simplicity, generality, and the possibility of versatile secondary modifications have promoted the PD coating method to be a promising coating strategy in many fields. Since the first report in 2007, PD coatings have been widely applied in different fields. Currently, the main drawback of the PD coating method is the lack of spatial and temporal control during the polymerization process, limiting its applications and making the mechanism investigations difficult. On the other hand, photo-assisted methods have been widely investigated and are known to be highly controllable. The idea of introducing the control offered by photo-assisted reactions into DA polymerization might result in a more controllable PD coating strategy. In this thesis, it was shown that reactive oxygen species (ROS), formed upon UV irradiation of oxygen-containing solutions, could serve as oxidants for DA. Therefore, UV light could be used to achieve a better control over the DA polymerization. I investigated the effects of UV irradiation on DA solutions. It was found that DA polymerization was accelerated by UV irradiation, and that under neutral conditions a well-controlled DA polymerization could be achieved. By cooperation with an antioxidant, sodium ascorbic acid (SA), DA polymerization in basic solutions can also be well-controlled. UV-triggered DA polymerization could be used toreflective absorption specotroscopy (IRRAS), time-of-flight secondary ion mass spectroscopy (ToF-SIMS), X-ray reflectivity (XRR) and scanning electron microscopy (SEM). In the part II, a photo based reversible surface modification strategy is demonstrated. Reversible surface modification represents a new generation of surface modification strategies because they are capable of producing reversible surfaces with reversible properties. Reversible surface exhibits significant advantages compared to normal functional surface, for example, the capability of “write and erase” process, possibility to renew and reuse the surface, formation of complex, multi-component and gradient patterns, capture-and-release properties, and the possibility of in-situ manipulation of local environments. However, currently most reported reversible surface functionalization strategies suffer from time-cost reversible cycle and non-controllable processes, which greatly limit potential applications of the method. In order to develop a smart reversible photopatterning strategy, I introduced a photodynamic disulfide exchange reaction as a method for surface modification. Surface photo-disulfide exchange was applied and characterized on a porous HEMA-EDMA surface. The results showed that reversible photopatterning could easily be achieved and that the kinetics of the exchange is extremely fast. A reversible photo functionalization/patterning strategy could also be obtained. The disulfide exchange reaction was investigated and analyzed by water contact angle (WCA) measurement, SEM, ToF-SIMS and microscopy. The part III describes a facile method to create a superhydrophobic surface on different substrates. Superhydrophobic surfaces hold great promise in a variety of applications where extreme water repellency can lead to novel properties and functionalities. Most of the existing techniques, however, require multi-step and laborious procedures as well as only applicable to certain substrates. In the last part of the thesis, I present a facile one-step (“paint-like”) method for creating superhydrophobic porous polymer coatings. The approach is based on the anionic polymerization of 2-octyl cyanoacrylate in the presence of aqueous ethanol. This leads to the formation of a highly porous superhydrophobic polymer film. The morphology of the porous structure could be controlled by varying the ethanol/water ratio. The method is fast, convenient, does not require any special equipment, and can be performed in the presence of oxygen. It was shown that the technique could be used to coat variety of materials, is applicable to three-dimensional substrates and leads to the formation of stable and strongly adherent superhydrophobic coatings. The surface was characterized by WCA measurement,and SEM.

Item Type: Dissertation
Supervisor: Grunze, Prof. Dr. Michael
Date of thesis defense: 29 May 2015
Date Deposited: 01 Jul 2015 10:09
Date: 2015
Faculties / Institutes: Fakultät für Chemie und Geowissenschaften > Institute of Physical Chemistry
Subjects: 540 Chemistry and allied sciences
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