In this Thesis, a dual-responsive hydrogel based on redox-responsive PFS and temperature-responsive PNIPAM was prepared. Taking advantage of its inherent redox-responsive properties, the hydrogels were employed as a reducing environment for the in-situ fabrication of AuNPs. Using the plasmonic photothermal effect of the formed AuNPs, AuNP-temperature responsive hydrogel composites can be remotely controlled by this efficient heat source activated by light irradiation. Based on the AuNP-stimuli responsive hydrogel synergies, we aimed at designing anisotropic structures to realize complex deformations and surface morphology changes controlled by both temperature and light and discovering the mechanism of deformation and the reaction stoichiometry of AuNP formation. The following topics will be presented and discussed in detail in this Thesis.
In Chapter 2, the background related to the major topics studied in this Thesis on AuNPs, stimuli-responsive hydrogels, nanocomposite hydrogels and anisotropic hydrogels are briefly reviewed from the perspective of structure design and applications.
In Chapter 3, a bilayer hydrogel with switchable surface morphologies is discussed featuring a compliant poly(acrylamide) bottom layer and a poly(N-isopropylacrylamide) top layer that contains in-situ fabricated AuNPs. Taking advantage of the plasmonic heating properties of the AuNPs, the appearance of wrinkles on the top layer can be induced by exposure to water and the disappearance can be switched by light irradiation or thermal heating.
In Chapter 4, to understand how the stress state impacts the development of patterns in the bilayer hydrogels described in Chapter 3, a series of bilayer hydrogels with different stress states are presented that exhibit elaborate patterns. By swelling the bottom layers in water for different periods of time, a dynamic evolution of surface patterns and patterns with complex features can be achieved through a decrease of the compressive strain to different degrees, which induced the decompression of the patterns to different extents.
In Chapter 5, an anisotropic PNIPAM/PVA hydrogel with PVA-reduced and -stabilized gold nanoparticles is discussed using a mechanical strain induced method. The synthesized AuNP/hydrogel nanocomposites showed anisotropic actuating behavior, triggered by the stimuli of temperature and light.
In Chapter 6, investigations of the stoichiometry reaction process of the PFS hydrogels in AuNP formation are presented. These materials are introduced in Chapter 3 and 4. Supersingly, about ten times more than the stoichiometric amount of AuNPs was formed in the reaction system with respect to employed ferrocene repeat units and the possible reasons for this are discussed.
