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Molecular Modeling of Self-assembly in Hydrophilic Macroionic Solutions and Mechanical Behaviors of Polymer Glass Materials

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2017, Doctor of Philosophy, University of Akron, Polymer Science.
The constant push for a molecular-level understanding of problems in soft condensed matter physics and the limitation of existing characterization techniques in providing such information has made molecular modeling an invaluable tool for modern science and technology. Two substantial problems that have drawn enormous interest and focus in recent years are facing this critical situation. These two problems are the unique self-assembly behaviors of hydrophilic macroionic solutions, and the special mechanical properties of polymer glass materials with high molecular weight. The first part of this dissertation is focused on understanding the intriguing self-assembly phenomena in hydrophilic macroionic solutions. Hydrophilic macroions represent a large group of soluble species, such as inorganic metal-oxide molecular clusters, biomacromolecules, and small nanoparticles. Like-charged hydrophilic macroions can self-assemble into hollow spherical single-layered super-molecular structures named “blackberry” in solution, when they have moderate surface charge density and size (between 1 nm and 10 nm). Macroionic solutions cannot be described by either Debye-Huckel theory for simple ions, as the large ions cannot be treated as point charges, or DLVO theory for colloids, as the macroions still form real solutions. In order to better understand this unique phenomenon, large-scale coarse-grained molecular dynamics simulations have been performed with a coarse-grained model specifically designed for this type of macroionic solutions. With this molecular modeling tool, we have attempted to answer the most outstanding questions regarding this special behavior, including: (1) what is the origin of the attractive force among like-charged soluble macroions? (2) is this attractive force, mediated by counterions, not due to van der Waals interactions? (3) how do the self-assembly behaviors change with macroionic charge density? (4) why is the size of the macroions crucial for this particular type of assembly to form? and (5) why do various macroions tend to form similar single-layered blackberry structures? The simulation results seem to provide satisfactory answers to these questions. In the second part of this dissertation, the special mechanical behaviors of polymer glass materials have been extensively studied using molecular modeling techniques, and the importance of chain connectivity in glassy polymers has been greatly highlighted. Polymer glass materials can be either ductile, undergoing yielding and necking, or brittle, suffering from crazing and brittle fracture. Until recently, there was no satisfactory molecular-level interpretation covering the whole spectrum of these special mechanical properties. Thus in this portion of the study, carefully designed polystyrene glass systems have been modeled using all-atom molecular dynamics simulation to investigate the effect of chain networking in terms of yielding that takes place in the presence of entangled long polymer chains embedded in short polymer chain systems. The simulation results are compared with a recently proposed molecular model, which suggests that the structural integrity, necessary to prevent brittle fractures, is due to the entangled chain network structure in glass polymers with high molecular weight. Continuing this work in the future should aid towards a complete understanding of the structure and property of polymer glass materials.
Mesfin Tsige, Dr. (Advisor)
Tianbo Liu, Dr. (Committee Chair)
Shi-Qing Wang, Dr. (Committee Member)
Toshikazu Miyoshi, Dr. (Committee Member)
Jutta Luettmer-Strathmann, Dr. (Committee Member)
199 p.

Recommended Citations

Citations

  • Liu, Z. (2017). Molecular Modeling of Self-assembly in Hydrophilic Macroionic Solutions and Mechanical Behaviors of Polymer Glass Materials [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1490801264398364

    APA Style (7th edition)

  • Liu, Zhuonan. Molecular Modeling of Self-assembly in Hydrophilic Macroionic Solutions and Mechanical Behaviors of Polymer Glass Materials. 2017. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1490801264398364.

    MLA Style (8th edition)

  • Liu, Zhuonan. "Molecular Modeling of Self-assembly in Hydrophilic Macroionic Solutions and Mechanical Behaviors of Polymer Glass Materials." Doctoral dissertation, University of Akron, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=akron1490801264398364

    Chicago Manual of Style (17th edition)