Selective adsorption of metal nanoparticles on block copolymer films through electrostatic interactions

  • Selektive Adsorption von Metall-Nanopartikel auf Block Copolymer Filmen anhand elektrostatischer Wechselwirkungen

Wagner, Tom; Böker, Alexander (Thesis advisor); Pich, Andrij (Thesis advisor)

Aachen (2016, 2017)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2016

Abstract

Abstract "Selective Adsorption of Metal Nanoparticles on Block Copolymer Films Through Electrostatic Interactions"The present thesis deals with the controlled hierarchical organization of ordered nanoscaled structures, which partly consist of physically active components, and bearing great potential for prospective industrial use. Through electrostatic attraction, negatively charged gold nanoparticles (AuNPs) are selectively deposited on positively charged nanostructured diblock copolymer films in order to generate ordered two-dimensional superstructures.The introduction introduces the reader into the fields of phase separated block copolymer films, metal nanoparticles and the theories of coulombic interactions on the nanoscale. The fabrication of block copolymer substrates as well as metal nanoparticle synthesis open up the experimental part, which is followed by the presentation of newly developed methodologies for the controlled adsorption of AuNPs on the basis of electrostatic attraction. Explanations on analytical methods for material characterization and process-monitoring end this section.At the beginning of the first main chapter (chapter 3), the manufacture of thin films consisting of polystyrene-block-poly-2-vinylpiridine (PS-b-P2VP) through spin-coating is discussed. Subsequently is described, the phase separation of these films under the influence of solvent vapors which cause the formation of alternating lamellae on the film surface. In chapter 4 is shown that the posterior vapor treatment with symmetric dihalides like diiodobutane (DIB) and/or diiodopropane (DIP) lead to nitrogen quaternization in the P2VP blocks (then becoming "qP2VP" blocks) and simultaneous electrostatic charging of the films. The chapter is finalized by a study of varied reaction conditions to further enhance the degree of quaternization in the qP2VP domains. Chapter 5 firstly describes the selective sequestration of AuNPs on qP2VP domains by immersion of the electrostatically charged films into AuNP solution. Here was found, that simple immersion enables large scale selective AuNP deposition on qP2VP domains. Similar results were obtained from films of hexagonally ordered micelles from the same polymer. In the second part of this chapter is demonstrated for the first time, that polydimethylsiloxane (PDMS) wrinkles, loaded with AuNPs, enable to print two-dimensional AuNP arrays on lamellar block copolymer films. Depending on the angle between the block copolymer lamellae and the PDMS wrinkles during printing, AuNP arrays of varying geometries could be received (rhomboid, rectangular). In the last chapter, a new methodology is presented enabling for real time monitoring of the electrostatically driven selective AuNP adsorption on the qP2VP domains, using in situ electrochemical impedance spectroscopy. The results show that the amount of adsorbed AuNPs correlates with the charge density in the qP2VP domains and thus allows control over the AuNP density on qP2VP domains. Ultimately, kinetic aspects of the selective AuNP adsorption as well as of the occurring electrochemical processes at the film|AuNP solution interface are elucidated.