Preparation And Properties Of CO₂-Responsive Nanofibers/Nanoparticles

Stimuli-responsive polymers can adapt to surrounding environments and change their physical or chemical properties on external stimuli. As one of the essential endogenous gases, carbon dioxide（CO₂） has good biocompatibility and biomembrane permeability. Morever, CO₂ is a widespreading, nontoxic, and “green” stimulus which is capable of reacting with amidines, tertiary amines, and guanidines. CO₂-responsive polymers can undergo reversible chemical and conformational changes on exposure to CO₂. With the development of nanotechnology, polymer science and biotechnology, a great deal of various CO₂-responsive nanomaterials have been developed which are widely used in the field of polymersomers, smart hydrogel and functional surfaces. In this thesis, based on CO₂-responsive macromolecules, electrospinning and magnetic nanoparticles were utilized to construct CO₂-responsive nanofibers and CO₂-responsive magnetic nanoparticles, respectively. A variety of characterization methods were used to study the morphologies, structures and CO₂-responsive properties of the nanomaterials, and explore their applications in oil/water “on-off” switches and controlled drug release.Specifically, based on the combination of polymerization reactions and the technique of electrospinning, CO₂-responsive electrospun nanofibers with diameter of 700 nm were successfully fabricated. The specific morphology and wetting property of the nanofibers were characterized. It is found that chemical composition and surface morphology are two important factors to influence the surface oil/water wettability. Upon treatment with CO₂, the obtained nanofibrous membrane is able to switch between hydrophobicity/oleophilicity and hydrophilicity/oleophobicity which make it good candidate as oil/water “on-off” switch. Furthermore, the combination of excellent responsive properties and porous nanostructure enables the “smart” membrane to be used to switch selective oil/water separation with high separation efficiency and good stability for different oil/water systems.In addition, CO₂-resonsive well-defined core-shell-corona structure magnetic Fe3O4@SiO2-poly（N,N-dimethylaminoethyl methacrylate）（PDMAEMA） nanocarriers were developed which combined thermal decomposition, sol-gel process and distillationprecipitation polymerization. The obtained magnetic hybrid nanoparticles had good water solubility and these materials could be easily guided by an external magnetic field. The hydrodynamic radius（Rh） of the magnetic hybrid nanoparticles could be adjusted by alternate CO₂/N2 treatment driving a switchable volume transition from contraction to expansion because of the CO₂ responsiveness of PDMAEMA. Importantly, the CO₂ induced reversible “on-off” transformation makes it possible to perform an accurate dosing release of doxorubicin（DOX） in vitro in a time-controllable manner. Moreover, in vitro cytotoxicity represented that the CO₂-responsive magnetic nanocarries have good biocompatibility and could be safely used in living systems.