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Manipulation of self-assembled nanostructures from molecular Janus particles based on polyoxometalates, polyhedral oligomeric silsesquioxanes and [60]fullerene

Liu, Hao
http://orcid.org/0000-0002-5704-4472
http://rave.ohiolink.edu/etdc/view?acc_num=akron1447529892

Abstract Details

2015, Doctor of Philosophy, University of Akron, Polymer Science.
The ability to manipulate self-assembly behaviors of molecular building blocks is the key to precise “bottom-up” fabrication of desired nanostructures. In this dissertation, we focus on the rational design, facile synthesis, and self-assembly of a series of molecular Janus particles (MJPs) constructed by chemically linking a-Keggin-type polyoxometalate (POM), Lindqvist-type POM, polyhedral oligomeric silsesquioxane (POSS) derivatives and [60]fullerene (C60) derivatives. This dissertation contains two sub topics. The first one describes a rational strategy to obtain self-assembled two-dimensional (2D) nanocrystals of MJPs with definite and uniform thickness. Three different types of MNPs, namely POSS derivative, C60 derivative, and Lindqvist-type POM, are used as building blocks to construct several amphiphilic molecular Janus particles by covalently connecting hydrophobic crystalline BPOSS with a charged hydrophilic MNP. The formation of 2D nanocrystals with an exact thickness of double layers of molecules is driven by directional crystallization of the BPOSS MNP and controlled by various factors such as solvent polarity, number of counter ions, and sizes of the MNPs. Strong solvating interactions of the ionic MNPs in polar solvents (e.g., acetonitrile and dimethylformamide) are crucial to provide repulsive interactions between the charged outlying ionic MNPs and suppress further aggregation along the layer normal direction. The number of counter ions per molecule plays a major role in determining the self-assembled morphologies. Size matching of the hydrophobic and ionic MNPs is another critical factor in the formation of 2D nanocrystals. Self-assembly of rationally designed molecular Janus particles provides a unique “bottom-up” strategy to engineer 2D nanostructures. In the second sub topic, the facile synthesis and solution self-assembly behaviors of another series of MJPs are discussed. a-Keggin type POM nanoclusters and isobutyl-substituted BPOSS cages are covalently connected at 1:1, 1:2 and 1:4 ratios to construct Keggin-BPOSS, Keggin-2BPOSS, and Keggin-4BPOSS in high yields. Self-assembled nanostructures of these precisely-defined MJPs are resulted from the competing crystallization processes of the POM and the BPOSS building blocks. Since the Keggin-type POM nanocluster is slightly larger than BPOSS in the cross-section areas perpendicular to the long axis of the MJPs, crystallization of Keggin-BPOSS in the acetonitrile/water mixture was mainly directed by the POM building block, leading to an interesting “micellar-crystal” transition towards one-dimensional (1D) nanobelts. Directional crystallization of the BPOSS cages, however, dominated the self-assembly of Keggin-2BPOSS and Keggin-4BPOSS in their methanol/chloroform mixtures where the cross-section area of the Keggin POM nanocluster is smaller than those of 2BPOSS and 4BPOSS perpendicular to the long axis of the MJPs, and resulted in the formation of 2D nanosheets with exactly two layers of MJPs constructed in a head-to-head structure along the thickness normal. The distinct results manifest that the self-assembly of these MJPs could be controlled by the directional crystallization of the dominating building blocks. A rational strategy may thus be possible: we can purposely control and tune diverse unconventional nanostructures via design and synthesis of those giant molecules which follow defined chemical and physical principles of self-assemblies.
Stephen Cheng (Advisor)
Yu Zhu (Committee Chair)
Tianbo Liu (Committee Member)
Toshikazu Miyoshi (Committee Member)
Robert Weiss (Committee Member)
Chemistry; Inorganic Chemistry; Polymer Chemistry
Nanosheet, Janus particles, Polyoxometalates, POSS, Fullerene, Self-assembly, Nanobelt

Recommended Citations

Citations

  • Liu, H. (2015). Manipulation of self-assembled nanostructures from molecular Janus particles based on polyoxometalates, polyhedral oligomeric silsesquioxanes and [60]fullerene [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1447529892

    APA Style (7th edition)

  • Liu, Hao. Manipulation of self-assembled nanostructures from molecular Janus particles based on polyoxometalates, polyhedral oligomeric silsesquioxanes and [60]fullerene. 2015. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1447529892.

    MLA Style (8th edition)

  • Liu, Hao. "Manipulation of self-assembled nanostructures from molecular Janus particles based on polyoxometalates, polyhedral oligomeric silsesquioxanes and [60]fullerene." Doctoral dissertation, University of Akron, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1447529892

    Chicago Manual of Style (17th edition)

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This open access ETD is published by University of Akron and OhioLINK.