Research

Research Summary

Research Activities and Techniques

Methodologies for Assembling Block Copolymers

The above Figure summarizes the methods, with exception to self-assembly, that we have developed systematically over the past 15 years for block copolymer nanostructure and hierarchical structure preparation.

Self-assembly is the basis of our research. It refers to the spontaneous segregation of the different blocks of a copolymers in either the solid state or in a block-selective solvent. Helical cylinders, multiple helices, and the space-filling-molecular-model morphology are some structures observed by us from the self-assembly of ABC triblock copolymers in block-selective solvents.

Directed assembly refers to block copolymer self-assembly under external constraints such as in confined volume, in 2-d space, or at a liquid/liquid interface. While directed assembly has been practiced in block copolymer thin films, we demonstrated the concept of directed assembly in solvents by combining emulsion formation with block copolymer self-assembly. This method has so far allowed us to prepare cell-like micro spheres with compartmentalized cores and virus-like particles with bumpy and chain-segregated surfaces etc.

Nanostructures prepared from block copolymer self assembly or directed assembly are held together by van deer Waals forces and may mutate or disappear when solvation conditions change. We developed systematically between 1994 and 2002 chemical processing, involving selective domain crosslinking and/or sculpting (degradation), of assembled block copolymers to yield “permanent”, “sculptured”, and “permanent sculptured” nanostructures. Novel structures prepared by us included nanofibers, nanotubes, thin films containing nanochannels, and nanospheres of many architectures.

We recently invented the controlled chemical coupling of different “permanent” and “permanent sculpted” nanostructures. Attaching a hydrophobic nanotube by end to a hydrophilic nanosphere yielded “super-surfactant”. We obtained “nanotube multi-blocks” by end-linking covalently nanotubes of different compositions.

Double assembly refers to the further assembly of micelles or coupled nanostructures of block copolymers into more complex or hierarchical structures. These are called double assembly because the block copolymers are assembled into micelles at level 1 and the micelles, either after or without chemical processing, are further assembled at level 2 into hierarchical structures.

Polymer/Inorganic Hybrid Nanostructures

We prepare polymer/inorganic hybrid nanostructures via two approaches. In approach 1, we hybridize block copolymer nanostructures via incorporating into them inorganic particles. In approach 2, we use block copolymers as surfactant to facilitate the direct preparation of polymer/inorganic hybrid structures. Example structures prepared by us including super-paramagnetic polymer/(iron oxide, Ni, or Co) nanospheres or microspheres, magnetic polymer/(iron oxide, Co, or Ni) nanofibers, as well as catalytic nanospheres and nanofibers.

Microscopy Images of Example Structures Prepared by Us

Applications of Nanostructured Polymer Materials

Oil-, Water-, and Stain-Resistant Surfaces

Prof. Guojun Liu of the Department of Chemistry and his post-doctoral fellow Dean Xiong are working with Dr. Scott Duncan, Defence R&D Canada Suffield, to develop oil-, water-, and stain-resistant surfaces. They can now covalently attach a low-surface-tension polymer onto glass and cotton fabric surfaces to render the desired resistance. The pictures below compare the behavior of dye-impregnated droplets of water and cooking oil on cotton fabric that was not and had been coated by Dr. Xiong using a polymer.


Training

Students and post-doctoral fellows receive rigorous training in our group for the sheer fact that our research activities are diversified ranging from polymer syntheses and characterization, nanostructure and hierarchical structure preparation and characterization to organic, physical, and inorganic chemistry. Most of us become versatile researchers before leaving this research group.

Significance

When we enter this field 16 years ago, polymer nanoscience and technology emcompassed only spherical particles of different architectures. It now deals with 1-d (nanofibers and nanotubes), 2-d (thin films containing nanochannels), and 3-d (HSs) structures with multiple technologies under commercialization. Our work together with those of others have helped and are continuing to help define and shape this field.