Advanced search options

Advanced Search Options 🞨

Browse by author name (“Author name starts with…”).

Find ETDs with:

in
/  
in
/  
in
/  
in

Written in Published in Earliest date Latest date

Sorted by

Results per page:

Sorted by: relevance · author · university · dateNew search

You searched for +publisher:"Clemson University" +contributor:("Dr. Stephen Creager"). Showing records 1 – 2 of 2 total matches.

Search Limiters

Last 2 Years | English Only

No search limiters apply to these results.

▼ Search Limiters


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

Record DetailsSimilar RecordsGoogle PlusoneFacebookTwitterCiteULikeMendeleyreddit

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 November 29, 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. 29 Nov 2020.

Vancouver:

Wickramasinghe ANK. Structural Study of Multifunctional Block Co-polymers in Solutions and Thin Films. [Internet] [Masters thesis]. Clemson University; 2017. [cited 2020 Nov 29]. 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

2. Etampawala, Thusitha. NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES.

Degree: PhD, Chemistry, 2013, Clemson University

This work focuses on interfacial structure and dynamics of structured polymers in thin films and in solutions using neutron techniques accompanied by atomic force microscopy. We probed polymers with a common theme that were highly segregated either because of presence of ionic groups or topological constraints. In these polymers the interfacial regions often define their function in different applications such as clean energy, printing adhesions and drug delivery systems. Thin film studies include systems of polystyrene/sulfonated polystyrene, a rigid sulfonated polyphenylene and polystyrene three-arm stars/linear polystyrene. The first two systems include ionic components and the last exhibits topological constraints. Polystyrene is often used as a model polymer because of the ease of exercising synthetic control over its molecular weight. Interdiffusion at the polymer-polymer interface was followed as well as diffusion of guest molecules. We found that the interfacial diffusion at the interfaces of ionic-nonionic polymers is strongly impacted by the presence of ions. The presence of ionic groups results in surface aggregation which in turn impacts the interfacial diffusion. The rigidity of the polymer also plays an important role as it results in significant interstitial spaces that dominate diffusion. The interfaces formed by these polymers are often inhomogeneous and contain both ionic and nonionic species that impact the onset of dynamics. In parallel, we studied the interfacial segregation of three-arm star polymers in a matrix of polystyrene. The contact point between the three-arms forms topological constraints that impact the segregation. The interfacial compositions were found to be balanced between entropic forces that drove polymer chain ends to the interfaces and the effects of topological constraints that hindered the motion of polymers. Interfacial segregation effects are seen not only in thin films but also strongly affect the assembly of polymers in solution. Here we studied a penta-block copolymer that consists of an ionic center block in hydrophobic solution. We found that very stable aggregates are formed where these shapes and stability are attributed to the ionic block. Finally the synthesis of structured alternating copolymers and their optical characteristics are introduced. Advisors/Committee Members: Dr. Dvora Perahia, Dr. Christopher J. Cornelius, Dr. Stephen Creager, Dr. Steven J. Stuart.

Subjects/Keywords: Block co-polymers; Interfacial Effects; Ionomers; Neutron Reflectometry; Small Angle Neutron Scattering; Thin Films; Physical Chemistry

Record DetailsSimilar RecordsGoogle PlusoneFacebookTwitterCiteULikeMendeleyreddit

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

APA (6th Edition):

Etampawala, T. (2013). NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES. (Doctoral Dissertation). Clemson University. Retrieved from https://tigerprints.clemson.edu/all_dissertations/1207

Chicago Manual of Style (16th Edition):

Etampawala, Thusitha. “NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES.” 2013. Doctoral Dissertation, Clemson University. Accessed November 29, 2020. https://tigerprints.clemson.edu/all_dissertations/1207.

MLA Handbook (7th Edition):

Etampawala, Thusitha. “NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES.” 2013. Web. 29 Nov 2020.

Vancouver:

Etampawala T. NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES. [Internet] [Doctoral dissertation]. Clemson University; 2013. [cited 2020 Nov 29]. Available from: https://tigerprints.clemson.edu/all_dissertations/1207.

Council of Science Editors:

Etampawala T. NEUTRON STUDY OF STRUCTURED POLYMERS AT INTERFACES. [Doctoral Dissertation]. Clemson University; 2013. Available from: https://tigerprints.clemson.edu/all_dissertations/1207

.