Structural and mechanical investigations of polyelectrolyte films
Polyelectrolyte films have received significant scientific interest due to their potential applications in a wide range of fields. A fundamental understanding of these films is vital as it forms the foundation for ensuring that the films' potential applications are given the best possible conditions for success. In this project, the focus has been on expanding the current fundamental understanding of specific types of polyelectrolyte films' response to changes in salt and pH.
Zwitterionic polymer films' reactions to increased salt concentration and specific types of ions have been the focus of an experimental study. It was found that the thickness of the films increased with the salt concentration to a degree that depended on the specific anions in the solution. By performing similar measurements on cationic and anionic polymer films, it was possible to understand how cross-linkages in the polyzwitterionic films were broken by anions while the effect of cations was to act as counterions and thereby increase the osmotic pressure. Both of these effects contribute to the increase in film thickness.
The increased understanding of the mechanisms of polyzwitterionic films was used to understand the response of a more complex film type. Multilayer films of weak polyelectrolytes are films formed with alternating layers of positively charged cationic and negatively charged anionic polymers. The weak nature of these polyelectrolytes means that their charge is affected by both pH and salt concentration, which in combination with their alternating structure in the multilayer makes this film type's response difficult to understand.
The multilayer films were formed under varied conditions, and their response to pH was then measured at different salt concentrations and with different ion types. Based on these measurements, it was possible to show that the multilayer films at the pH values at which they were built had almost neutral overall charge and at high pH had an excess of negative charge. In cases where the charge was equal, the understanding of zwitterionic films could be used to describe the multilayer film's thickness change with increased salt concentration. Similarly, the film's thickness change at high pH could be described as a combination of a traditional weak polyanionic film and the polyzwitterionic film.
Principal Supervisor:
Professor Esben Thormann, DTU Chemistry
Co-supervisor:
Associate Professor Rene Wugt Larsen, DTU Chemistry
Examiners:
Professor Günther Peters, DTU Chemistry
Associate Professor Torbjörn Pettersson, KTH, Sweden
Associate Professor Per Lyngs Hansen, Aarhus University
Chairperson:
Associate Professor Martin Nielsen, DTU Chemistry