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Molecular Ordering, Structure and Dynamics of Conjugated Polymers at Interfaces: Multiscale Molecular Dynamics Simulations

Yimer, Yeneneh Yalew
http://rave.ohiolink.edu/etdc/view?acc_num=akron1416796729

Abstract Details

2014, Doctor of Philosophy, University of Akron, Polymer Science.
Polymer-based solar cells (PSCs) require significant improvements in efficiency and life time in order to be commercially viable. Interfacial structure and morphology dictate the performance of PSCs, and these properties in turn depend on processing conditions and surface chemistry. To optimize device performance, detailed knowledge of the factors most critical to the molecular-level structure, morphology and dynamics of donor/acceptor systems at interfaces will be necessary. For one promising donor, poly(3-hexylthiophene (P3HT), we have utilized all-atom and coarse-grained molecular dynamics simulations to investigate such properties at liquid/vacuum, solid/liquid and solid/solid interfaces. At liquid/vacuum interfaces, static and dynamic properties of P3HT films and their dependence on temperature and molecular weight were studied. P3HT chains showed ordering through preferential exposure of side-chain at the interface, and surface tension showed strong dependence on temperature and molecular weight. Properties such as self-diffusion coefficients, chain end-to-end distance and torsion autocorrelations were also utilized to quantify the dynamics of the P3HT chains in the film. Both static and dynamic properties of P3HT were found to be in agreement with well-known models for polymers. Subsequent simulations of P3HT/water systems offered insight into the wetting behavior of P3HT and the nature of the solid-liquid interface in crystalline and amorphous P3HT. From contact angle calculations, different P3HT surfaces were determined to be hydrophobic. In the time scale of our simulations, no observable change in the orientation of the P3HT at interfaces was observed. Furthermore, the molecular ordering of P3HT close to substrates is expected to be the key to device performance. Ordering of P3HT chains at the interface can be tuned by altering the substrate surface chemistry. We investigated the effect of surface chemistry on the ordering of P3HT on self-assembled monolayers (SAMs) of n-alkanethiols. The results showed that the ordering of P3HT strongly depends on the P3HT-SAM interactions. The effect of solvent on the P3HT-SAM interactions was also studied. In addition, we characterized the surface properties of pure SAMs on gold {111}. The end-functionalized network structure was found to be correlated to the adsorption sites. For P3HT/acceptor systems, all-atom simulations are challenging because of the need to access large spatial and temporal regimes. To overcome this, we developed a coarse-grained model for P3HT based on the all-atom force field. The coarse-grained model showed good agreement with bulk and interfacial properties obtained from the all-atom model and has a great potential for analyzing morphology and dynamics of P3HT/acceptor blends.
Mesfin Tsige, Dr. (Advisor)
Dhinojwala Ali, Dr. (Committee Member)
Perry David, Dr. (Committee Member)
Miyoshi Toshikazu , Dr. (Committee Member)
Liu Tianbo, Dr. (Committee Member)
198 p.
Materials Science; Physics; Polymers
Conjugated polymers, interfacial properties, multiscale modeling, molecular dynamics simulations, self-assembled monolayers

Recommended Citations

Citations

  • Yimer, Y. Y. (2014). Molecular Ordering, Structure and Dynamics of Conjugated Polymers at Interfaces: Multiscale Molecular Dynamics Simulations [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1416796729

    APA Style (7th edition)

  • Yimer, Yeneneh. Molecular Ordering, Structure and Dynamics of Conjugated Polymers at Interfaces: Multiscale Molecular Dynamics Simulations . 2014. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1416796729.

    MLA Style (8th edition)

  • Yimer, Yeneneh. "Molecular Ordering, Structure and Dynamics of Conjugated Polymers at Interfaces: Multiscale Molecular Dynamics Simulations ." Doctoral dissertation, University of Akron, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=akron1416796729

    Chicago Manual of Style (17th edition)

akron1416796729
482
© 2014, some rights reserved.Creative Commons License Molecular Ordering, Structure and Dynamics of Conjugated Polymers at Interfaces: Multiscale Molecular Dynamics Simulations by Yeneneh Yalew Yimer is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. Based on a work at etd.ohiolink.edu.
This open access ETD is published by University of Akron and OhioLINK.