Synthesis of Responsive Polymer Brushes for Sensing Applications

During the past decades the field of sensors has been subject to much attention due to an increased demand for (bio)sensors and environmental monitoring. The efforts have been concentrated to create sensors which are reliable, highly sensitive and selective, small and fast responding. Surface modification by polymer coating has been proven an excellent method to introduce selectivity on actuators. Among the various techniques that allow the formation of polymer thin film, polymer brushes have gained attention along the past decades due to their unique structure and the possibility offered by controlled/"living" surface-initiated radical polymerization technique to generate polymer thin film with precisely controlled thickness, composition and architecture. Polymer brushes have found numerous applications including nonbiofouling surfaces and cell adhesive surfaces, protein binding and immobilization, chromatography supports, membrane functionalization, responsive surface, antibacterial coatings or low friction surfaces. Despite their interesting properties and the numerous reports describing the potential of polymer brush as responsive surface, their use for "real" sensing applications has receive little or no attention so far. This Thesis describes how polymer brushes can be employed as selective surface modification for sensing application. We aimed at synthesizing polymer thin film able to detect analytes of interest, with a particular focus on low detection limit and high selectivity. After a short introduction to the field of polymer brushes (Chapter 1), Chapter 2 presents a review of the work accomplished in the field of responsive polymer brushes with an emphasis on solvent responsive, thermoresponsive, pH- and ion-sensitive polymer brushes. The pH-induced swelling and collapse of surface-tethered, weak polyelectrolyte brushes is of interest not only for the development of responsive surface coatings but also for the pH controlled transport or adsorption. Chapter 3 discusses results of an extensive series of quartz crystal microbalance (QCM) experiments that aimed at further understanding the influence of brush thickness and density on the pH-responsiveness of poly(methacrylic acid) (PMAA) brushes and developing strategies that allow to engineer the pH responsiveness and dynamic response range of PMAA based brushes. It was observed that due to their high grafting density, the apparent pKa of surface-tethered PMAA differs from that of the corresponding free polymer in solution and also covers a broader pH range. The pKa of the PMAA brushes was found to depend both on brush thickness and density; thicker brushes showed a higher pKa value and brushes of higher density started to swell at higher pH. The second part of this section demonstrates the feasibility of the N-hydroxysuccinimide-mediated post-polymerization modification to engineer the pH responsiveness of the PMAA brushes. By using appropriate amine functionalized acids, it was possible to tune both the pH of maximum response as well as the dynamic response range of these PMAA based polyelectrolyte brushes. In Chapter 4, benzo-15-crown-5 functionalized polymer brushes prepared via surface-initiated atom transfer radical polymerization were used as the active layer in a potassium-selective QCM sensor. The polymer brushes allowed the selective detection of potassium ions, even in the presence of a large excess of sodium ions and the sensitivity of the sensor could be tuned by varying the brush thickness. Chapter 5 demonstrates the possibility to use peptide functionalized polymer brush, prepared via surface-initiated atom transfer radical polymerization (SI-ATRP), to probe heavy metal ions via voltammetric based methods. The polymer brush enhanced the mercury (II) ions sensitivity as compared to the bar electrode and allowed the detection of mercury down to the nanomolar concentration range. Furthermore it was demonstrated that the heavy metal recognition is a reversible and reproducible process. Post-polymerization modification reactions are widely employed to prepare functional polymer brushes. Relatively little is known, however, about the distribution of functional groups in such post-modified brushes. Using neutron reflectivity and UV-visible spectroscopy as principal tools, Chapter 6 investigates the p-nitrophenyl chloroformate (NPC) mediated post-polymerization modification of poly(2-hydroxyethyl methacrylate) (PHEMA) brushes, prepared via surface-initiated atom transfer radical polymerization, with D-10 leucine and D-3 serine. The neutron reflectivity experiments indicate that the post-polymerization modification depends both on the brush thickness and density. Whereas, for dense brushes, post-polymerization modification with D-10 leucine is limited to the top ∼ 200 Å of the brush, independently of the brush thickness, the extent of post-modification can be significantly extended by decreasing brush density, or by using the more hydrophilic and sterically less demanding D-3 serine, which reflects the ability of this amino acid to more readily penetrate the brush. UV-vis. experiment revealed that the NPC activation is also non-uniform, but brush thickness and density dependent, which adds to brush thickness, density and the nature of the amino acid as another of a complex set of variables that determine the final distribution of functional groups in post-modified brushes

A Potassium-Selective Quartz Crystal Microbalance Sensor Based on Crown-Ether Functionalized Polymer Brushes

Benzo-15-crown-5 functionalized polymer brushes prepared via surface-initiated atom transfer radical polymerization are used as the active layer in a potassium-selective quartz crystal microbalance sensor. The polymer brushes allow the selective detection of potassium ions, even in the presence of a large excess of sodium ions and the sensitivity of the sensor can be tuned by varying the brush thickness

Degradable Polymer Brushes Prepared via Surface-Initiated Controlled Radical Polymerization

Hydrolytically degradable polymer brushes would represent an interesting platform for the development of functional coatings for various biomaterials applications In this manuscript, the surface- initiated atom transfer radical copolymerization of 5.6-benzo-2-methylene1,3-dioxepane (BMDO) and poly(ethylene glycol) methacrylate (PEGMA) has been investigated to prepare degradable po;ymer brushes. The copolymerization of BMDO and PEGMA results in brushes that contain hydrolytically labile ester linkages in the polymer backbone. The thickness of these polymer brushes can be controlled via the polymerization time and the BMDO content by adjusting the monomer feed composition The degradation of the brushes was investigated by ellipsometry and atomic force microscopy (AFM) experiments While the brushes were relatively stable under neutral and mild-basic conditions (pH 9), degradation was significantly enhanced under acidic conditions Degradation was found to be accelerated at low pH values (pH 3-5) and with increasing BMDO conten

Demonstration von Flexibilitätsoptionen im Gebäudesektor und deren Interaktion mit dem Energiesystem Deutschlands : FlexGeber ; Abschlussbericht

Ziel des Projektes ist es neuartige Wärme- und Kälteerzeugungstechnologien sowie neue Lösungen zur Steigerung und Qualitätssicherung der Energieeffizienz und zur Integration erneuerbarer Energien in drei Case Studies - in GHD und Industrie - zu demonstrieren. Es soll gezeigt werden, wie die einzelnen Sektoren Strom, Wärme und Kälte effizient gestaltet werden können und durch eine Verknüpfung das Potenzial zur Flexibilisierung in der Industrie und im GHD-Sektor gehoben werden kann. Hierfür werden Markt- und Betreibermodelle entwickelt, die die Schnittstellen der Sektoren adressieren und die Einbindung der GHD- und Industriebetriebe in die Energiewirtschaft schaffen. Es werden zudem die identifizierten Flexibilitätsoptionen im Gebäudesektor in ein regionales und deutschlandweites Energiesystem- und Energiemarktmodell eingebunden, um deren Interaktion mit dem Energiesystem und die damit verbundenen Auswirkungen zu bewerten. Das Projekt hat nicht nur das Ziel, mit einem breiten Blick den Nutzen einer Flexibilitätserhöhung in verschiedenen Gebäudetypen zu analysieren, sondern wird im Rahmen der Case Studies in konkreten Anwendungsfällen das Flexibilitätspotenzial heben und dadurch eine direkte Auswirkung auf die Erhöhung der Flexibilität im deutschen Energiesystem erreichen und die Energiewende vorantreiben. In den Case Studies wird u.a. auch detailliert untersucht, welche Investitionen in Mess-, Steuer- und Regelungstechnik (MSR-Technik), flexible Energiewandler und -Speicher nötig sind, um die Flexibilität in den Gebäuden signifikant zu erhöhen und damit einen positiven Beitrag zur Energiewende zu leisten. Die identifizierten Maßnahmen werden im Rahmen des Projekts in den Case Studies implementiert und technisch-wirtschaftlich analysiert

Crumb rubber modified binders

RILEM Technical Committee 279 WMR is dedicated to the Valorization of Waste and Secondary Materials for Roads. Its Task Group 2 investigated Crumb Rubber (CR) as an additive to enhance the performance of bitumen. CR recycled from end-of-life tires (ELTs) was chosen for this investigation because crumb rubber modified bitumen (CRMB) has been used to improve bituminous mixtures performance for fatigue and reflective cracking. The success of these mixtures is due to the CRMB viscosity that allows the use of an increased amount of bitumen compared to conventional mixtures. Because the viscosity of the CRMB is a function of the CR surface, and presently various types of CRs are produced, it is crucial to verify how these materials perform as a bitumen modifier. Interlaboratory experiments were performed on four types of CR, obtained from mechanical grinding, cryogenic process, waterjet pulverization and reacted and activated rubber. Three base, 35/50, 50/70 and 70/100, bitumen were used for the modification. Mechanical and chemical properties of CRMB were investigated. Despite some differences in the non-mechanical tests, i.e., penetration, softening point and viscosity, the results of the mechanical tests (complex shear modulus) suggest that the bitumen penetration grade ultimately dictates CRMB response.- (undefined