Theses and Dissertations from UMD

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New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM

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Subject: search.filters.subject.small angle neutron scattering

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Now showing 1 - 4 of 4
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    Processing and structural characterization toward all-cellulose nanocomposites
    (2021) Henderson, Doug A; Briber, Robert M; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Cellulose is the most abundant biopolymer on the planet and is used in a variety of industry sectors including paper, coatings, medicine, and food. A deep understanding of cellulose is important for its development as an alternative polymer to those based on petroleum. This work focuses on two cellulose systems. The first of these, cellulose nanofibers, are the basic structural elements of naturally-occurring cellulosic materials; they exhibit excellent mechanical characteristics due to high crystallinity and a dense network of hydrogen bonding. These fibers can be separated from bulk cellulose via a TEMPO oxidation reaction followed by mechanical homogenization into a suspension in water. In this work, the production of these fibers is investigated by monitoring the change in structure of cellulose as a function of TEMPO reaction time and mechanical homogenization using small angle neutron scattering, atomic force microscopy, and optical microscopy. The second cellulose system is a molecular solution of cellulose formed using a binary solvent mixture consisting of ionic liquid and an aprotic solvent. Cellulose is difficult dissolve due to a dense hydrogen bonding network, and ionic liquids have been shown to be an effective alternative to more hazardous and energy-intensive dissolution methods for cellulose currently used in industry. The phase behavior of these solutions has been investigated using small angle neutron scattering as a function of temperature. The process of regenerating cellulose from these solutions is also investigated, as dense gels of cellulose and ionic liquid were produced with a unique multiscale ordered structure. The ultimate goal of this work is to combine cellulose nanofibers and molecular cellulose solutions in order to create all-cellulose nanocomposite films. These films are characterized using tensile testing, atomic force microscopy, and water uptake measurements in order to understand the interaction between cellulose nanofibers and molecular cellulose solutions, water resistance and tunability of mechanical properties.
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    Characterization of Iron Oxide Nanoparticles in Structural Silk-elastinlike Protein Polymer
    (2012) Shih, Jennifer; Briber, Robert M; Material Science and Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The structure of silk elastin-like protein (SELP) block copolymers containing Fe3O4 magnetic nanoparticles are investigated. These materials have potential applications for hyperthermia cancer therapy. SELPs undergo a gel transition at physiological temperatures, which can be used to localize delivery of nanoparticles at tumor sites. Vibrating sample magnetometry (VSM), transmission electron microscopy (TEM), and small angle neutron scattering (SANS) are used to characterize the nanoparticles and the SELP-nanoparticle nanocomposite system. A series of nanoparticles with three different nominal diameters, 30, 50 and 80 nm, were added to 4 and 8 wt.% SELP samples. Different functionalities on the nanoparticle surface affect their interactions with SELP. The 50 nm nanoparticles in SELP exhibit chaining (linear association of the nanoparticles), while the 30 nm nanoparticles are too small and settle out of the polymer mesh and the 80 nm nanoparticles tend to cluster without any regard for SELP structure. The SELP concentration does not have a major affect on nanoparticle behavior in the nanocomposites.
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    Micelle and Aggregate Formation in Amphiphilic Block Copolymer Solutions
    (2010) Clover, Bryna Christine; Greer, Sandra C; Chemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The amphiphilic nature of many block copolymers causes self-aggregation and micelle formation in solvents that are miscible with only one of the block polymers (selective solvents). Micelle and aggregate formation of amphiphilic block copolymers in selective solvents is a function of temperature and concentration. Such self-aggregation has been examined here in a variety of block copolymer systems. In dilute solutions of Pluronic P85 (PEO26PPO40PEO26) (where PEO is poly(ethylene oxide) and PPO is poly(propylene oxide)) in D2O, transitions between clustered unimers, spherical micelles, cylindrical micelles, and finally lamellar micelles were observed with increasing temperature. The effect of pressure on this system was examined through small angle neutron scattering (SANS) techniques. At temperatures above 95 oC, a new phase of “demixed lamellae” was observed. Pressure effects on the transition temperatures between the phases of this system were investigated. The self-aggregation of Reverse Pluronic 17R4 (PPO14PEO24PPO14) in D2O has also been examined. The phase diagram of this system was determined through visual cloud-point techniques. Three distinct regions have been observed in solutions of this system, as a function of temperature and concentration: a cloudy, one-phase region; a clear, one-phase system; and a region of phase separation. Copolymer structures were examined in the clear and cloudy one-phase regions through SANS and dynamic light scattering (DLS) techniques. A network, or clustering, of unimers was observed in the cloudy phase. Aggregates in the clear, one-phase region could not be identified definitively as micelles. Finally, micellization of PEO132-PB89 (where PB is polybutadiene) has been studied in solutions of deuterated methanol and deuterated cyclohexane. Spherical micelles were observed in solutions of deuterated methanol. These micelles change little in size or shape over a 50 oC temperature span. The difference in aggregates in protonated and deuterated solvents was also examined. In deuterated cyclohexane, the copolymer formed flexible, cylindrical micelles below 40 oC. These micelles became spherical in shape at higher temperatures.
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    A Biophysical Study of Clathrin Utilizing Light Scattering, Neutron Scattering and Structure Based Computer Modeling
    (2007-04-27) Ferguson, Matthew Lee; Nossal, Ralph J; Losert, Woflgang; Physics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    A principal component in the protein coats of certain post-golgi and endocytic vesicles is clathrin, which appears as a three-legged heteropolymer (known as a triske- lion) that assembles into polyhedral baskets principally made up of pentagonal and hexagonal faces. In vitro, this assembly depends on the pH, with baskets forming more readily at low pH and less readily at high pH. We have developed procedures, based on static and dynamic light scattering, to determine the radius of gyration, Rg, and hydrodynamic radius, RH, of isolated triskelia under conditions where basket assembly occurs. Calculations based on rigid molecular bead models of a triskelion show that the measured values can be accounted for by bending of the legs and a puckering at the vertex. We also show that the values of Rg and RH measured for clathrin triskelia in solution are qualitatively consistent with the conformation of an individual triskelion that is part of a "D6 barrel" basket assembly measured by cryo-EM tomography. We extended this study by performing small angle neutron scattering (SANS) experiments on isolated triskelia in solution under conditions where baskets do not assemble. SANS experiments were consistent with previous static light scattering ex- periments but showed a shoulder in the scattering function at intermediate q-values just beyond the central diffraction peak (the Guinier regime). Theoretical calcula- tions based on rigid bead models of a triskelion showed well-defined features in this region different from the experiment. A flexible bead-spring model of a triskelion and Brownian dynamics simulations were used to generate a time averaged scattering function. This model adequately described the experimental data for flexibilities close to previous estimates from the analysis of electron micrographs.