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You searched for +publisher:"Clemson University" +contributor:("Dr. Dvora Perahia, Committee Chair"). Showing records 1 – 2 of 2 total matches.

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Clemson University

1. Wickramasinghe, Anuradhi Nimesha Kumari. Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films.

Degree: MS, Chemistry, 2017, Clemson University

This work focuses on the association of a structured multifunctional co-polymer in solutions and thin films as studied using neutron techniques and atomic force microscopy. Tethering multiple blocks into structured architectures is a promising way to tailor block copolymers with well-defined properties. Polymer films are often cast from solutions. Therefore, understanding the association of complex polymers in solutions and the impact of the aggregates into thin films is crucial to design materials with well-defined properties. Ionically-decorated blocks facilitate transport of ions and response to electrical fields. However they also affect the polymer structure. This work is divided into two sections. The first one resolves aggregation of a symmetric van der Waals pentablock polymer in solutions. The second follows film structure as charged groups are introduced. Specifically, we probed the assembly of polymers having an A-B-C-B-A co-polymer architecture, where co-polymer C is polystyrene, B is hydrogenated poly (ethylene-r-propylene) and A is poly (t-butyl styrene). In solutions we studied non-ionic pentablock polymers and in thin films we studied ionic pentablock polymers. In the solution study, the solvent polarity was tuned by controlling the ratio of cyclohexane to propanol. We find that, in contrast to most block copolymers, this pentablock polymer associates into fractal aggregates in cyclohexane which become more self-similar with increasing temperature. Increasing solvent polarity, by addition of propanol, drives the collapse of pentablock chains which leads the formation of more spherical aggregates. The structured architecture of the pentablock polymer enhances entropy resulting in less well-defined shapes that are maintained over a broad temperature range. In thin films, we probed the ionic analog of the above co-polymer where C is a randomly sulfonated polystyrene with sulfonation fractions of 0, 26 and 52 mole %, as the sulfonation level and thermal annealing times are varied using atomic force microscopy, surface tension measurements and neutron reflectivity. Our results show that as cast films form layers with both hydrophobic blocks dominating the solid and air interfaces and the ionizable block segregates to the center. With annealing at 170°C, above Tg of styrene sulfonate, the films coarsen, with surface aggregation dominating the structure, though interfacial regions remain dominated by the hydrophobic segments. Advisors/Committee Members: Dr. Dvora Perahia, Committee Chair, Dr. Stephen Creager, Dr. Rhett Smith.

Subjects/Keywords: block copolymers

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Wickramasinghe, A. N. K. (2017). Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films. (Masters Thesis). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_theses/2687

Chicago Manual of Style (16th Edition):

Wickramasinghe, Anuradhi Nimesha Kumari. “Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films.” 2017. Masters Thesis, Clemson University. Accessed December 01, 2020. https://tigerprints.clemson.edu/all_theses/2687.

MLA Handbook (7th Edition):

Wickramasinghe, Anuradhi Nimesha Kumari. “Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films.” 2017. Web. 01 Dec 2020.

Vancouver:

Wickramasinghe ANK. Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films. [Internet] [Masters thesis]. Clemson University; 2017. [cited 2020 Dec 01]. Available from: https://tigerprints.clemson.edu/all_theses/2687.

Council of Science Editors:

Wickramasinghe ANK. Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films. [Masters Thesis]. Clemson University; 2017. Available from: https://tigerprints.clemson.edu/all_theses/2687


Clemson University

2. Aryal, Dipak. Computational Insight into Structured Ionic Co-polymers from Molecule to Membrane.

Degree: PhD, Chemistry, 2017, Clemson University

Impact of ionizable blocks on structure and dynamics of structured ionic co-polymers in solutions, melts, and thin films has been studied using atomistic molecular dynamics simulations. Much of the interest in ionic block co-polymers derives from their inherent tendency to phase segregate into hydrophobic and hydrophilic domains. Ionic domains in ionic block co-polymers serve as physical cross-linkers and form a long-range percolated cluster assembly, which is a crucial component to transport ions or solvents for varieties of applications from clean energy to biotechnology. One of such ionic co-polymers, where ionic blocks facilitate the transport and other non-ionic blocks provide chemical and mechanical stability, is pentablock (ABCBA) co-polymer. It consists of randomly sulfonated polystyrene (C) in the center, tethered to poly-ethylene-r-propylene (B), terminated on both sides by poly-t-butyl styrene (A). This dissertation focuses on the studies of these co-polymers in their different forms, including the single chains to micelles in solutions, membrane, and followed by water penetration into their thin films. Single chains were studied as a function of nature of solvents including the 1:1 mixture of cyclohexane/heptane and water. This specific hydrophobic solvent is used in industrial casting processing. Water is a highly prevalent substance in the environment and is a by-product of many eletrochemical reactions. We find that a single molecule of the ionic co-block polymer even undergo internal segregation into ionic and non-nonic blocks in both solvents. We then probed the assembly of the pentablock copolymer in solutions to understand the structural diffrences between the micelles formed by the ionic copolymer and van der Waals polymers. Micelles are the building blocks of a membrane, and a key step to engineer controlled polymeric ion transport systems. We find that the ionic network serves as a long lived skeleton of the assembled co-polymers where the hydrophobic blocks are able to migrate in and out of this structure depending on the nature of the solvents. Following the understanding of micellizaion of polymers we moved to melts. We find that the melts form intertwined networks of t-b-PS and center PS blocks. These networks are independent of the degree of sulfonation and have no long-range ordering. The sulfonated groups form different size of clusters where their cohesiveness and morphology affect both collective and segmental dynamics of all the blocks. Studies have been further exteneded to focus on the interfacial behaviour of complex copolymer thin films in solvent environments. We find that inerfacial response of hydropbobic and hydrophilic blocks including their dynamcis differs from the bulk ones. We aslo observe a multi-steps water penetration process. Onset of slow penetration is observed at the early stage where water molecules first transverse the hydrophobic rich surface before reaching to the hydrophilic regime. Water molecules then diffuse along the… Advisors/Committee Members: Dr. Dvora Perahia, Committee Chair, Dr. Gary S. Grest, Dr. Brian Dominy, Dr. Steven J. Stuart.

Subjects/Keywords: Ionic Block Copolymer; Molecular Dynamics Simulations

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Aryal, D. (2017). Computational Insight into Structured Ionic Co-polymers from Molecule to Membrane. (Doctoral Dissertation). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/1984

Chicago Manual of Style (16th Edition):

Aryal, Dipak. “Computational Insight into Structured Ionic Co-polymers from Molecule to Membrane.” 2017. Doctoral Dissertation, Clemson University. Accessed December 01, 2020. https://tigerprints.clemson.edu/all_dissertations/1984.

MLA Handbook (7th Edition):

Aryal, Dipak. “Computational Insight into Structured Ionic Co-polymers from Molecule to Membrane.” 2017. Web. 01 Dec 2020.

Vancouver:

Aryal D. Computational Insight into Structured Ionic Co-polymers from Molecule to Membrane. [Internet] [Doctoral dissertation]. Clemson University; 2017. [cited 2020 Dec 01]. Available from: https://tigerprints.clemson.edu/all_dissertations/1984.

Council of Science Editors:

Aryal D. Computational Insight into Structured Ionic Co-polymers from Molecule to Membrane. [Doctoral Dissertation]. Clemson University; 2017. Available from: https://tigerprints.clemson.edu/all_dissertations/1984

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