The Application Of Two-Dimensional UV-vis Correlation Spectroscopy In Two Types Of Polymer Films

The graduate thesis concerns the application of two-dimensional (2D) UV-vis correlation spectroscopy in two types of polymer films. 2D correlation spectroscopy was first proposed by Noda. Later, he made some improvements and extended it into generalized 2D correlation spectroscopy. 2D correlation spectroscopy has offered convenience in separation and assignment of the overlapped bands, as it can significantly enhance the spectral resolution of the conventional one-dimensional (1D) spectroscopy. Meanwhile, more detailed investigations of different spectral variables in one system are possible and the specific order of the changes can be probed via 2D correlation analysis, which provides theoretical arguments for the exploration of the mechanisms under corresponding perturbation. Based on these advantages, 2D correlation spectroscopy is widely used in various fields. In the thesis, 2D correlation technique is combined with UV-vis spectroscopy and applied to the studies of the structures and mechanisms of the layer-by-layer multilayer films and drug-containing polymer films. The work described here has largely extended the application area of 2D UV-vis correlation spectroscopy, for the property of electronic spectroscopy has greatly limited the structural study of polymers via UV-vis spectroscopy.The thesis is divided into four parts.Chapter I is an introduction of the entire work, discussing the main analytical method, 2D correlation spectroscopy, used in this thesis in detail, including the history, basic principles and properties. The practical applications by 2D correlation analysis with different ways of characterizations are also briefly reviewed. Chapter II is about the study of layer-by-layer multilayer films released in different pH conditions. The ultra-thin films are assembled by alternate adsorption via hydrogen-bonding interaction between poly(3-thiophene acetic acid) (PTAA) and poly(4-vinyl-pyridine) (PVP). Subsequently, the multilayers are immersed in the aqueous solutions of different pH values. UV-vis spectroscopy is primarily employed here to monitor the removal of the polymers from the substrate after the broken of the diving force. With the help of 2D correlation spectroscopy, it is found that the polymers in the films show diverse phenomena at different pH values. In alkaline solution, the elimination of PTAA takes place before PVP, and the extent and speed of elimination is relatively large. In acid solution, the removal of these two polymers adopts a reverse order, and the extent of elimination is much smaller.On the basis of the above work, we attempt to add gold nanoparticles in the PTAA/PVP films to investigate the elimination of Au-containing films under the same pH conditions. To exclude the influence of the interaction between PTAA and gold nanoparticles, PAA/PVP-Au system is selected for comparison. It is found that the films with gold nanoparticles are stable when changing the pH values of the aqueous solution, and the polymers are difficult to be removed from the substrate. The interaction between the gold particles and the neighboring PVP chains is responsible for the phenomenon. Gold particles act as physical cross-link points in the multilayers and connect the polymers. Due to the interaction, the stability of the Au-containing multilayer film is ensured even though the changes in pH values may result in the break of the hydrogen bonds.Chapter III focuses on the study of drug release process in the phosphate-buffered saline (PBS) of the drug-containing polymer film. UV-vis spectroscopy is utilized to monitor the release process of ibuprofen and piroxicam from PMMA film under time perturbation. Both of the drugs maintain a continuous release process. Furthermore, 2D UV-vis correlation spectroscopy is applied to explore the sequence of the drug release and it is implied that hydrogen-bonding interaction is formed between ibuprofen and PMMA, which is responsible for the lower release speed of ibuprofen than that of piroxicam. FTIR spectra of drug-containing PMMA film confirm the existence of the interaction.Chapter IV is the conclusion to the whole research work. 2D UV-vis correlation analysis is applied to the study of layer-by-layer multilayer films, and two studies are derived from it. One is the elimination process of Au-containing layer-by-layer film at different pH values. The other is the 2D UV-vis application in drug-containing polymer film. The former is introduced in Chapter II as the extension of the study of the layer-by-layer films, while the latter is depicted in Chapter III as another application of 2D UV-vis correlation spectroscopy.