Institutional Repository
The UDSpace Institutional Repository collects and disseminates research material from the University of Delaware.
- Faculty, staff, and graduate students can deposit their research material directly into UDSpace. Faculty may use UDSpace to fulfill the University of Delaware Faculty Senate Open Access Resolution, and in many cases may use it to fulfill open access requirements from grant funding agencies.
- Departments can use UDSpace to publish or distribute their working papers, technical reports, or other research material.
- UDSpace also includes all doctoral dissertations from winter 2014 forward, and all master's theses from fall 2009 forward.
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2025, 21th Issue, part 2
(Newark, Del.: Chesapeake Pub. Corp., 2025-05-23) Newark post
2025, 21th Issue, part 1
(Newark, Del.: Chesapeake Pub. Corp., 2025-05-23) Newark post
Morphological Control in the Design of Bio-Inspired, Stimuli-Responsive, Bilayer Hydrogels
Klincewicz, Francis Gregory
The development of next-generation responsive polymeric systems requires materials with built-in practical functionality within the structure. Nature has provided many muses for the design of these “smart” stimuli-responsive materials, particularly hydrogels. For example, the pinecone has inspired bilayer hydrogel systems that curve upon application of a stimulus due to a contraction mismatch between interfaced responsive, “active” and non-responsive, “passive” hydrogels. However, as the stimuli-responsive polymer field has developed, there is a need for understanding the impact of hydrogel morphology on the actuation of bilayer hydrogels. In this thesis, the thermal response of bilayer hydrogels is linked to the morphological changes caused by nanofillers and the synthetic solvent in the component active, stimuli-responsive hydrogels.
First, to study the effect of morphological changes induced by synthetic solvent, the thermal response of hydrogel bilayers fabricated via digital light processing (DLP) 3D printing is tuned using a cosolvent mixture. These bilayers are comprised of a thermally-responsive hydrogel, poly(N-isopropyl acrylamide) (pNIPAAm), and a non-responsive hydrogel, poly(2-hydroxyethyl acrylate) (pHEA). By printing these hydrogels from either ethanol or an ethanol-water solution, morphological changes including pore size are enacted in the pNIPAAm hydrogels, while the pHEA hydrogels are relatively unaffected. These morphological changes are correlated to a decreased thermal response with increased presence of water during printing due to the formation of a hydrophobic “skin” layer upon heating of the hydrogel. This skin layer is also observed in bilayer hydrogels formed by interfacing pNIPAAm and pHEA hydrogels. A comparison to an existing theoretical model is shown to have poor agreement with the experimental data, which is quantified using a “correction factor.” This research showcases precursor solution solvent as a handle to tune the morphology of bilayer hydrogels and presents limitations with existing theory.
Extending these research findings, montmorillonite (MMT) clay is explored as a filler to potentially improve water transport to accelerate the thermal response of the bilayers fabricated in Chapter 1 using the solvent mixture. The introduction of surface hydrophilicity by the clay is hypothesized to mitigate the formation of the skin layer within the active pNIPAAm layer of the bilayers printed from the ethanol-water cosolvent mixture. Through exploration of single-layer active hydrogels, the addition of MMT is shown to cause faster actuation than the clay-free control, which is attributed to a decrease in skin layer formation. However, at higher MMT loading, the size of clay-rich domain structures is shown to correlate to a decreased initial rate of actuation and final magnitude of actuation. By interfacing these pNIPAAm/MMT hydrogels with pHEA hydrogels, bilayers are formed and shown to actuate considerably faster and to a greater curvature than the clay-free control. The increased bilayer actuation is related to the ability of the active layer to exert a contractile force on the passive layer during contraction, which is evidenced by improved prediction by the existing theoretical model which had shown poor predictive capability in Chapter 2. This research demonstrates the impact of inorganic, hydrophilic nanofillers for accelerating the response of bilayers through inhibition of skin layer formation and improvement of contractile force.
Finally, the impacts of the loading and the structure of non-isocyanate polyurethanes (NIPUs) on the melt rheology and mechanical properties of blends with poly(lactic acid) (PLA) are investigated for potential use in 3D printing. Pendent methoxy groups on the lignin-derivable NIPU are hypothesized to improve blend melt strength and viscosity compared to the methoxy-free, petroleum-derived NIPU due to intermolecular interactions. The potential for plasticization or rubber toughening by the NIPUs is investigated through thermal and rheological characterization of the phase morphology. The inclusion of NIPU within PLA is shown to decrease the relaxation time and viscosity of the blend compared to the neat PLA due to the NIPU likely being incorporated into a singular phase with the PLA. The Young’s moduli, yield strength, strain-at-break, and toughness of the blends are found to be generally comparable to the properties of the neat PLA, demonstrating a lack of plasticization. However, in both the melt and the solid state, the properties of the lignin-derivable NIPU are shown to slightly exceed the petroleum-derived NIPU, potentially illustrating the increased intermolecular interaction by the pendent methoxy groups. This research serves as a preliminary study for potentially 3D-printable materials as well as how polymer processing aid structure and loading may affect polymer blend rheology and mechanical properties.
Markedness Relations in the L2 Perception of English Obstruents by Arabic Speakers
Alkahtani, Faisal
This dissertation investigated the effect of markedness theory on second language (L2) speech perception. Markedness theory was developed based on the observation of speech output (i.e., speech production) of first language (L1) speakers. Research on speech productions showed that L2 speakers also exhibit similar patterns to L1 where the effects of markedness theory play a role in the learning process. Specifically, L2 speakers were found to have more difficulty with marked sounds than unmarked sounds. However, there is not a large body of research that focus on how markedness theory plays a role in the speech perception process. In this study, the perception of Arabic speakers learning English of 8 English obstruents were investigated to see if the effects of markedness would be exhibited. Specifically, the study attempted to see if voiced obstruents would be more difficult to perceive than voiceless obstruents and if sounds in word final position would be more difficult to perceive than in word initial position. Arabic was chosen as a case study since Arabic has voicing gaps in its obstruents phonemic inventory which runs counter to implicational universals. Specifically, while Arabic has the marked sound /b/, it lacks the unmarked sound /p/. An experiment was conducted where 31 Arabic participants and 31 native English speakers participated. They listened to nonce words containing the target sounds (/p/, /b/, /f/, /v/, /s/, /z/, /t/, and /d/), and they were asked to match auditory stimuli with visual representations of the nonce words that appeared on a screen. Results showed mixed patterns; Arabic speakers showed greater perceptual accuracy to sounds in initial position than final position confirming the principle that initial position is unmarked relative to final position. On the other hand, there was no significant difference between the perception of voiced and voiceless obstruents in initial position. This indicates that markedness theory doesn’t apply to L2 speech perception as it does to L2 speech production. In fact, it seems that phonetic factors played more prominent role on the participants' behavior. This research has significant implications for theory and practice that are discussed in the study in light of the existing knowledge of the problem under investigation.
Non-Local Game Homomorphisms
Hoefer, Gage
In the past few decades, the connections between non-local games arising in quantum information theory and the theory of operator algebras have undergone a phase of significant development. Operator algebras provide a particularly fruitful framework for approaching questions of non-locality in quantum systems, as the input-output behavior of measurements on bipartite quantum systems can be encoded through noncommutative operator algebras and their state spaces. This thesis is the compilation of a series of papers, written by the author in collaboration with Ivan G. Todorov, utilizing this framework by using the theory of operator algebras and completely positive maps to study questions involving non-local games.
Using the simulation paradigm from information theory, we define a quantized version of homomorphisms and isomorphisms between classical hypergraphs, generalizing quantum homomorphisms and isomorphisms of graphs from the literature. We show that these quantum homomorphisms and isomorphisms constitute pre-orders and equivalence relations, respectively. We use quantum homomorphisms of hypergraphs to provide multiple examples of strict separation between correlation classes of varying types. Specializing to the case when our underlying hypergraphs arise from classical non-local games, we define quantum non-local game homomorphisms and isomorphisms. We also show how the existence of a homomorphism or isomorphism of some fixed type between games is reflected in a comparison of optimal and asymptotic game values with respect to this type. These non-local game homomorphisms are defined via a new class of non-signalling correlations which we introduce here. We develop the multivariate tensor product theory in the category of operator systems, which we then use to provide a characterization of game homomorphisms in terms of state spaces for various tensor products of canonically associated operator systems. We then apply these results to the study of synchronous non-local games, defining jointly synchronous correlations and showing how they correspond to tracial states of tensor products of C*-algebras canonically associated to each game party.
We then move to a second level of quantization by proposing a "quantized" notion of hypergraphs (where "quantum" here is in the sense of a non-commutative analogue for a discrete combinatorial object), and introduce quantum homomorphisms between these quantum objects. We provide an initial foray into the properties quantum morphisms between quantum hypergraphs display, showing they satisfy analogous properties to quantum homomorphisms between classical hypergraphs. We also indicate initial connections these quantum homomorphisms between quantum hypergraphs have to the study of quantum input-output games. We end the thesis showing that homomorphisms of a local type between quantum hypergraphs is closely related, and in some cases identical, to the TRO equivalence of finite-dimensionally acting operator spaces canonically associated with each hypergraph. This suggests a quantum information theoretic approach to Morita equivalence in the category of operator spaces.