PhD Thesis
One-dimensional Hybrid Nanomaterials Based on Cylindrical Polymer Brushes
Jiayin Yuan (03/2005-09/2008)
Support: Axel H. E. Müller
Summary
Cylindrical polymer brushes (CPBs) have been synthesized via the combination of anionic polymerization (for the backbone) and atom transfer radical polymerization (for the side chains) via the grafting from technique to achieve a narrow molecular weight distribution in both the backbone and the side chains. They were employed as template for the preparation of various types of one-dimensional (1D) polymer-inorganic hybrid nanomaterials.
In the case of well-defined core-shell superstructured CPBs, depending on the aimed functional 1D hybrid nanostructures, different combinations of core and shell have been chosen. CPBs with a poly(3-acryloylpropyl trimethoxysilane) core and a poly(oligo(ethylene glycol) methacrylate) shell were hydrolyzed by aqueous ammonia to produce water-soluble organo-silica hybrid nanowires. Since the trimethoxysilyl group was directly incorporated into the structure of the CPB, the addition of an external inorganic precursor in this case is avoided. These hybrid nanowires can form a lyotropic phase and serve as in-situ template for the pyrolytic formation of inorganic silica nanowires.
Amphiphilic CPBs with a hydrophilic poly(acrylic acid) (PAA) core and a hydrophobic poly(n-butyl acrylate) (PnBA) shell were used as cylindrical templates and nanoreactors for the fabrication of semiconductor CdSe nanowires, due to the coordination ability of PAA with Cd2+ ions. Since the chemical structure of the PAA core was resumed, a double-loading process was carried out to load more CdSe nanoparticles into the CPB. AFM, TEM and UV-Vis characterizations have proven the increasing amount of CdSe in the hybrids.
Bishydrophilic CPBs with a poly(2-hydroxyethyl methacrylate) (PHEMA) core and a poly(oligo(ethylene glycol) methacrylate) (POEGMA) shell were employed for the fabrication of a worm-like assembly of TiO2 semiconductor nanoparticles, forming a kind of titania-CPB hybrid nanowires. The titanium alkoxide precursor were introduced into the CPB via a transalcoholysis reaction between Ti(OC4H9)4 and the PHEMA block. The titania-CPB hybrid nanowires were used to generate anatase titania nanowires via pyrolysis at 550 °C.
In general, all these inorganic nanowires templated by the core-shell CPB showed very uniform size in length as well as diameter, due to the low molecular weight distribution of the CPB backbone and the side chains. The shell of the CPBs protected the fabricated inorganic nanowires from agglomeration, and in addition, renders the hybrid nanomaterials soluble in various solvents, including water.
Poly(methyl methacrylate) (PtBMA) homopolymer CPBs were used to support the formation of uniform single-crystalline tellurium nanorods (length up to 822 nm, D ~ 36.1 ± 7.9 nm, aspect ratio from 2.7 to 22) at room temperature in THF. These rods with polymer attached on their surface aree very stable in THF, and were able to assemble tellurium or magnetite (Fe3O4) nanoparticles on the Te nanorods. The strategy to synthesize the Te nanorods was further extended to linear PtBMA polymers with high molecular weight. The assembly of Fe3O4 nanoparticles on these Te nanorods was controlled by the stoichiometric ratio of the nanoparticles and nanorods. The Fe3O4-decorated Te nanorods are superparamagnetic. They were aligned in the presence of an external magnetic field when dried from THF solution on a solid substrate.
These novel one-dimensional hybrid nanomaterials based on CPBs can have many potential applications due to their electronic, optical, semiconducting, and magnetic properties.