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We are particularly interested in understanding the role of hydrogen bonding interactions in self-assembly and phase separation in block copolymer systems. The thermodynamics and molecular mechanisms governing nanoscale morphology formation and related applications are addressed. Establishing the phase behaviour of block copolymers and their mixtures is accomplished through extensive use of transmission electron microscopy and small-angle X-ray scattering, along with atomic force microscopy and dynamic light scattering.
Phase behaviour in diblock copolymer/homopolymer systems. We study both theoretically and experimentally the microphase separation induced by competitive hydrogen bonding in A-b-B/C diblock copolymer/homopolymer systems. Hydrogen bonding interactions are correlated with the phase behaviour in terms of the difference in association constants K (Hameed, N., Salim, N. V. and Guo, Q., J. Chem. Phys. 2009, 131, 214905).
The phase behaviour of A-b-B/C diblock copolymer/homopolymer systems is studied theoretically according to the random phase approximation.
To investigate how hydrogen bonding determines the self-assembly and causes morphological transitions in different A-b-B/C diblock copolymer/homopolymer systems, we introduce the K values as a new variable into the phase diagram which we established for the first time.
Self-assembled complexes and blends. We have shown that the disparity in intermolecular interactions in block copolymer/homopolymer systems leads to the formation of self-assembled, nanostructured complexes (Hameed, N., Liu, J. and Guo, Q., Macromolecules 2008, 41, 7596). Formation of hierarchical nanostructures in block copolymer/homopolymer blends of PCL-b-P2VP and phenoxy was also observed (Hameed, N. and Guo, Q., Polymer 2008, 49, 922). In self-assembled diblock copolymer/homopolymer blends of P2VP-b-PMMA and phenoxy, core-shell micelles can be formed and uniformly dispersed in a continuous microphase of phenoxy (Salim, N. V., Hameed, N. and Guo, Q., J. Polym. Sci. Part B: Polym. Phys. 2009, 47, 1894 & front cover of the issue). The interplay between crystallization and microphase separation strongly influences the morphology and properties in double crystalline diblock copolymer/homopolymer blends with competitive hydrogen bonding interactions (Salim, N. V., Hanley, T. and Guo, Q., Macromolecules 2010, 43, 7695).
Vesicles in water. Vesicles in water were successfully prepared by complexation of an amphiphilic block copolymer and a polyelectrolyte homopolymer for the first time. A variety of vesicular morphologies, including small vesicles and large compound vesicles, were directly visualized in polystyrene-block-poly(ethylene oxide)/poly(acrylic acid) complexes in aqueous solutions using cryo-TEM. These findings suggest a viable approach to polymer vesicles in aqueous media.
Multiple vesicles and morphological transitions in aqueous solutions. Multiple vesicular morphologies were formed in PS-b-PAA/PS-b-PEO complexes in aqueous solution. Interconnected compound vesicles (ICCVs) were observed as a new morphology (shown below), along with a variety of aggregated nanostructures including vesicles, multilamellar vesicles (MLVs), thick-walled vesicles (TWVs) and irregular aggregates. Morphological transitions occurred with increase of the molar ratio [EO]/[AA]. With [EO]/[AA] up to 0.5 only vesicles were found whereas the MLVs appeared at [EO]/[AA] = 1. TWVs and ICCVs were formed with [EO]/[AA] = 2 and 6, respectively. Irregular aggregates occurred at [EO]/[AA] = 8 and above.