Smart Materials And Nanostructure Based On Host-guest Chemistry And Macromolecular Self Assembly

Macromolecular self-assembly is the process that polymers (or macromolecules capped precursors) form well-defined structure driven by various weak interactions (van der waal’ force, hydrogen-bond, electrostatic interaction, hydrophobic interaction etc). Currently, Macromolecular self-assembly becomes an important approach to construct new structures and new functional materials. Host-guest chemistry is an core contents of supramolecular chemistry, as well as important driving force of self-assembly. As the respective second generation and fourth generation of host molecules, cyclodextrin and cucurbituril have attracted extensive attention due to their unique structure and properties. In aqueous solution, cyclodextrin and cucurbituril can selectively encapsulate different organic molecules, inorganic molecules and biomolecules to form host-guest complexes. Because inclusion complexation between host and guest is greatly dependent on their matching degree (e.g.β-Cyclodextrin is more favorable to form inclusion complexes with adamantane than azobenzene), configuration (e.g. azobenzene), valence state (e.g. ferrocene or viologen and naphthalene) of guest molecules, formation and dissociation of the inclusion complex can be controlled by chemical induction, photo-irradiation or electrochemistry. These inclusion complexation systems have great potentials in designing and preparing stimulated functional materials and supramolecular nano-devices. This thesis majorly starts from this background, and contains four parts as follows:I. Dual stimuli-responsive hybrid supramolecular hydrogel AZO-(PDMA-b-PNIPAM) block copolymers with azobenzene groups on one end, themo-sensitive PNIPAM block on the other end and hydrophilic PDMA block in the middle were prepared through RAFT polymerization. In aqueous solution, the block copolymer and β-CD@QDs can form novel star-shaped hybrid inclusion complexes (HIC) in which β-CD@QDs nanoparticles is the core and block copolymer is the shell with PNIPAM block as the out layer. The supramolecular structure was confirmed by a combination of techniques, including UV-Vis spectrum, TGA, DLS and TEM. When the solution temperature was heated above LCST, HIC solution with a concentration above7wt%would form hydrogel due to the hydrophobic aggregation of PNIPAM block at the out layer. The sol-gel transition and hydrogel formation mechanism was studied by rheology. The inclusion complexation between azobenzene groups of AZO-(PDMA-b-PNIPAM) block copolymers and cyclodextrin on the surface of β-CD@QDs nanoparticles as well as collapsed PNIPAM domains served as two different and independent crosslinks. Then, gel-sol transition occurred when competitive host or guest, i.e. α-cyclodextrin or adamantane was added or the solution temperature was cooled below LCST of PNIPAM. Furthermore, the mechanism of the gel-sol transition and dissociation mechanism of hydrogel following the two external stimuli were quantitatively studied by rheology. The effects of polymerization degree of block copolymers, molar ratio between block copolymer and β-CD@QDs nanoparticles on hydrogel formation as well as fluorescence properties of HIC at different temperature were also studied.II. Supramolecular hybrid hydrogel from noncovalently functionalized graphene with block copolymer Water soluble (3-cyclodextrin surface-functionalized graphene was prepared via amine-epoxy reaction from ethylenediamino-(3-cyclodextrin and graphene oxide, which was further noncovalently functionalized with azobenzene-end functionalized AZO-(PDMA-b-PNIPAM) block copolymer to form brush-like hybrid graphene inclusion complexes (HGIC). HGICs have inorganic graphene nonosheets as the core, block copolymer as the shell and PNIPAM block at the out layer. The core and the shell were connected by inclusion complexation. Structure of resulted HGIC was fully characterized by a combination of techniques including TGA, UV-vis spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, TEM and AFM. The HGIC of10wt%concentration can quickly form supramolecular hybrid hydrogel as a result of aggregation of PNIPAM at the out layer when the temperature was close to its LCST. The sol-gel transition and formation mechanism was investigated by dynamic rheology and viscosity-temperature measurement. Seven different HGICs was prepared through inclusion complexation between CD-G and seven block copolymers with different polymerization degree. Viscous/elastic modulus and viscosity of the HGICs with temperature variation was fully investigated by dynamic rheology and viscosity-temperature measurement. The results show that gel point Tgel and viscosity turning points Tη increased with the ratio of degree of polymerization of PDMA block to PNIPAM block of HGIC superstructure. It was also found the hydrogel formation of HGIC was more quickly than that of HIC and the gelation temperature of HGIC was much lower than that of the HIC when the same temperature increase rate, the same block copolymer (Rm) and the same concentration were used. This may be attributed that the flexible and ultrathin2D planar structure of graphene sheets were more favored in the three-dimensional gel network formation.III. Noncovalently connected Micelles driven by Host-stabilized charge transfer interaction Hydrophilic copolymer containing two violegen moieties at the side chain (P(Mv-co-DMA)) and naphthalene end functionalized PNIPAM (Np-PNIPAM) was prepared, respectively, which can form graft-like copolymers in the presence of Cucurbit[8]uril. The formation of the copolymer driven by host-stabilized charge transfer interaction was confirmed by UV-Vis spectrum. The resultant copolymers can further self-assemble into non-covalently connected micelles (NCCM) above LCST of PNIPAM chains. Formation of micelle was monitored by DLS and TEM image shows spherical structure with diameter of200-250nm. DLS results also showed that Rh decreased greatly after adding reduced agent. Part work of this chapter is still in process.IV. Supramolecular hydrogel driven by host-stabilized charge transfer interaction Three different copolymers with naphthalene as the side chain and viologen dimer were designed and prepared. A primary research was performed on the formation of supramolecular hydrogel driven by host-stabilized charge transfer interaction, when the CB[8] was added.