Kalpana Katti

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2007 University Distinguished Professor (UDP) | Civil Engineering
https://www.ndsu.edu/ccee/faculty_and_staff/faculty/katti_kalpana/

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Browsing Kalpana Katti by Subject "Molecular dynamics"

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    Clay Fluid Interactions in Montmorillonite Swelling Clays: A Molecular Dynamics and Experimental Study
    (North Dakota State University, 2012) Patwary, Md Zillur R.
    Swelling clays cause tremendous amounts of damage to infrastructure. For the effective prevention of detrimental effects of these clays, and to optimize the beneficial properties for industrial applications it is necessary to clearly understand the fundamental mechanisms of swelling of clays. In this study, we studied the effect of fluid polarity on swelling and flow properties of swelling clays using molecular modeling and experimental technique for bridging the molecular level phenomenon of these clays with microstructure change, particle breakdown and macro scale swelling and flow properties. A wide range of fluids (Dielectric Constant 110 to 2.4) were used, those are also commonly present in landfill leachates. We were able to tie the properties of swelling clays at different length scales. Then, we simulated the solvation of clay sheets, studied the effect of discrete charge distribution, contribution of edge charges on swelling clays and discussed some fundamental assumptions associated with double layer theories.
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    Influence of Molecular Interactions on Elastic Properties and Oxygen Diffusion in PolyButylene Terephthalate Polymer: A Molecular Dynamics Study
    (North Dakota State University, 2012) Raviprasad, Muniyamuthu
    In most barrier applications, both mechanical and diffusion properties of the material are important. In this thesis the evaluation of molecular mechanisms responsible for the enhanced elastic properties of Polymer Clay Nanocomposites (PCNs) and the molecular mechanisms of Oxygen diffusion in PolyButylene Terephthalate polymer are presented. Interaction energy between PCN constituents, conformational changes of polymer, interaction energy between Oxygen molecule and polymer, rate of Oxygen and Oxygen diffusion coefficient are evaluated. Molecular simulation studies of PolyButylene Terephthalate (PBT) clay nanocomposite and Nylon6 clay nanocomposite show that a higher crystallinity polymer such as PBT would require higher attractive and repulsive interactions with organic modifier in order to make significant change in the crystallinity of PBT in the nanocomposite and in turn enhance the elastic modulus and hardness. Molecular interactions energy between Oxygen molecule and polymer, change in polymer conformation caused by thermal energy assist the Oxygen molecule to diffuse through polymer.
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    An Investigation of Mechanics of Collagen and Fibril in Bone and Interactions in Swelling Clays: A Molecular and Multiscale Modeling Study
    (North Dakota State University, 2012) Pradhan, Shashindra Man
    A fundamental study of the mechanics at the molecular scale and bridging it to the continuum level through multiscale modeling is the focus of this work. This work investigates how the material properties of nanoscale systems are influenced by the nonbonded interactions and molecular conformations. The molecular model is then bridged with the finite element model to link mechanics at nanoscale with the continuum scale. This work provides an unprecedented insight into how the interactions at the molecular scale influence mechanical properties at higher scales. Two materials are considered for the molecular modeling study: bone and Na-montmorillonite swelling clay. Bone is composed of composed of collagen molecules and hydroxyapatite in the molecular scale, which are organized into collagen fibril. The molecular dynamics study is carried out to study the nature of collagen-hydroxyapatite interface and the mechanics of collagen in bone. Furthermore, the molecular model of full-length collagen is built for the first time to show the differences in its conformation and deformation mechanism during pulling as compared to the short molecules, upon which the current understanding of is based. The mechanics of collagen is explained with the help of three-tier helical hierarchy not seen in short molecules. Two mechanisms of deformation and conformational stability of collagen are proposed: (i) interlocking gear analogy, and (ii) interplay between level-1 and level-2 hierarchies, the hydrogen bonds acting as an intermediary. The multiscale model of collagen fibril is developed by bridging nanomechanical molecular properties of collagen into the finite element model. This model shows that the molecular interactions between collagen and mineral significantly affect the mechanical response of collagen fibril. The deformation mechanism of collagen fibril and the effect of collagen crosslinks are also elucidated in this study. In recent years Na-montmorillonite has been proposed for bone regenerative medicine, besides other existing engineering applications. The molecular dynamics study of Na-montmorillonite at different levels of hydration is carried out to understand the role played by molecular interactions in the swelling behavior of Na-montmorillonite. This study greatly adds to our understanding of clay swelling, and provides important insights for modeling exfoliation and particle breakdown in clay.