A. James Clark School of Engineering
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The collections in this community comprise faculty research works, as well as graduate theses and dissertations.
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Item Cellulose Nanocomposites of Cellulose Nanofibers and Molecular Coils(MDPI, 2021-07-30) Henderson, Doug; Zhang, Xin; Mao, Yimin; Hu, Liangbing; Briber, Robert M.; Wang, HowardAll-cellulose nanocomposites have been produced from cellulose nanofiber (CNF) suspensions and molecular coil solutions. Morphology and small-angle neutron scattering studies show the exfoliation and dispersion of CNFs in aqueous suspensions. Cellulose solutions in mixtures of ionic liquid and organic solvents were homogeneously mixed with CNF suspensions and subsequently dried to yield cellulose composites comprising CNF and amorphous cellulose over the entire composition range. Tensile tests show that stiffness and strength quantities of cellulose nanocomposites are the highest value at ca. 20% amorphous cellulose, while their fracture strain and toughness are the lowest. The inclusion of amorphous cellulose in cellulose nanocomposites alters their water uptake capacity, as measured in the ratio of the absorbed water to the cellulose mass, reducing from 37 for the neat CNF to less than 1 for a composite containing 35% or more amorphous cellulose. This study offers new insights into the design and production of all-cellulose nanocomposites.Item SYNTHESIS OF POROUS FILMS FROM NANOPARTICLE AGGREGATES AND STUDY OF THEIR PROCESSING-STRUCTURE-PROPERTY RELATIONSHIPS(2005-12-09) Ogunsola, Oluwatosin Abiola; Ehrman, Sheryl H; Chemical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Porous films made from titania nanoparticle aggregates have a variety of uses in high surface area applications such as gas sensors, photocatalysts in treatment of wastewater and air pollutants, optical filters, and photovoltaic electrodes for low cost solar cells. A hybrid process based upon gas-to-particle conversion and particle precipitated chemical vapor deposition was used to synthesize porous films of titania nanoparticle aggregates. The residence time of particles in the reactor was varied and the influence on particle morphology and mechanical properties was studied. An increase in residence time resulted in an increase in primary particle diameter but did not significantly affect aggregate diameter, over the range of residence times considered in this study. The Young's modulus is shown to increase with a decrease in primary particle diameter. A study of the effect of post processing annealing on the particle morphology and mechanical properties was conducted. Increasing the annealing temperature resulted in particle growth at different temperatures and aggregate growth only at the highest temperature studied. The Young's modulus, however, shows only an influence of aggregate diameter, increasing as aggregate diameter increased. It is interesting to note that annealing did not result in a significant increase in Young's modulus or hardness until most of the surface area was lost. This suggests that annealing may not be the most effective process for strengthening films, if preservation of high surface area is desired. To better understand the effect of change in particle and aggregate diameters on Young's modulus, Monte Carlo and continuum methods were employed to explore structure-property relationships. A Monte Carlo method was used to simulate particle deposits and a finite element method was used to calculate the Young's modulus from strain energy of the deposits simulated. The results of this study indicate that a decrease in particle diameter increases the Young's modulus, especially below 15 nm. Aggregate size was not seen to have any effect on the Young's modulus, for the range of aggregate sizes considered. The results of these studies can be used to optimize the mechanical properties of titania films, made up of nanoparticle aggregates, for different desired applications.Item Characterization of the Behavior of Ultra-High Performance Concrete(2005-03-24) Graybeal, Benjamin Allen; Albrecht, Pedro A; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In the past decade significant advances have been made in the field of high performance concretes. The next generation of concrete, Ultra-High Performance Concrete (UHPC), exhibits exceptional strength and durability characteristics that make it well suited for use in highway bridge structures. This material can exhibit compressive strength of 28 ksi, tensile strength of 1.3 ksi, significant tensile toughness, elastic modulus of 7600 ksi, and minimal long-term creep or shrinkage. It can also resist freeze-thaw and scaling conditions with virtually no damage and is nearly impermeable to chloride ions. Prestressed highway bridge girders were cast from this material and tested under flexure and shear loadings. The testing of these AASHTO Type II girders containing no mild steel reinforcement indicated that UHPC, with its internal passive fiber reinforcement, could effectively be used in highway bridge girders. A large suite of material characterization tests was also completed. Based on this research, a basic structural design philosophy for bridge girder design is proposed.