In recent years, new research emphasis has been directed towards integrating multiple functions into polymeric materials. Among these new advances in materials science functional polymers with structural designs are intended to produce a specific polymer function. One group of these polymeric materials are the so-called smart hydrogels. Such polymers undergo a discontinuous or continuous large volume change transition in response to a small environmental stimulus such as temperature, pH-value, ionic strength, etc. The swelling characteristics of these networks have been studied extensively with regards to their use in micro devices or drug delivery systems.In order to utilize thin films of responsive hydrogels based on poly(N-isopropyl-acrylamide) (pNIPAAm) as active matrix in sensor applications, detailed knowledge about their structural and dynamical properties as well as their response to external stimuli is required. In the present study such dynamical and structural changes by swelling and collapsing were studied using Surface Plasmon Resonance / Optical Waveguide Spectroscopy (SPR/OWS) with dissipation. In combination with the reversed Wentzel-Kramers-Brillouin (rWKB) and Bruggeman effective medium approximation and by modelling the hydrogel film as a composite of sublayers with individual complex refractive indices, refractive index/volume fraction gradient profiles perpendicular to the surface are accessible simultaneously with information about local inhomogeneities. The imaginary refractive index of each sublayer can specifically be interpreted as a measure for static and dynamic inhomogeneities, which were found to be highest at the critical collapse temperature in the layer centre. These results indicate that the hydrogel collapse originates rather from the film centre than from its boundaries.Furthermore, the influence of silica nanoparticles, solvent and film thickness to the swelling behaviour and transition temperature was investigated.Moreover time-resolved quantitative studies of protein-functionalized hydrogel films are shown as well as the use of hydrogel supported protein-tethered bilayer lipid membranes as a new approach toward polymer-supported lipid membranes.
|Date of Award||19 Jun 2013|
|Supervisor||Toby Jenkins (Supervisor)|