Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 100 for “"free volume"”.
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Free Volume Manipulation Techniques of Polymer Membranes for Gas Separations
… structures, which increase the amount of free volume and gas throughput. The combination of high permeability and good selectivity exhibited by many PIMs have placed them near or above the Robeson upper bound, a standard metric used to compare polymer membrane performance. However, free …
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The effect of free volume on the radiation acceleration of creep in polycarbonates.
Thesis: B.S., Massachusetts Institute of Technology, Department of Chemical Engineering, 1967
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Triptycenes as a molecular building block to introduce internal free volume in organic materials
… 1. Triptycenes are shown to possess "internal free volume" swept out between their aromatic faces, which enable them to align their long axis normal to the host alignment to most efficiently fill this volume. This alignment is the opposite of that expected by conventional aspect ratio …
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Gas transport properties in polycarbonate - Influence of the cooling rate, physical aging, and orientation
… glassy polymers is directly correlated with the free volume content. Free volume arguments are indeed commonly used to explain the gas transport process. The gas transport properties of bisphenol-A polycarbonate films were examined as a function of the cooling rate, physical aging, and …
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Positron interactions with oriented polymers and with chiral quartz crystals
… with a focus on the size and density of free volume and hole relaxation properties in polycarbonate (PC) and polymethylmethacrylate (PMMA); fundamental studies of polarized positron interaction with chiral crystals were also studied. Free volume relaxation in PC and PMMA with different …
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Novel molecular architectures from iptycene polymers
… structural property called internal molecular free volume. When these bulky pendant groups are incorporated into the backbone of a polymer chain, they produce a novel chain architecture called molecular barbed wire. This molecular barbed wire architecture not only influences individual polymer …
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Experimental and Theoretical Verification of the Applicability of Homogeneous Combustion in a Porous Reactor to Internal Combustion Engines
… reactors differ considerably from conventional, free volume systems. Therefore these processes were investigated fundamentally as well as all associated thermo-dynamical and process models. This is the first reported attempt to investigate these processes in porous reactors under engine-relevant …
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The durability of adhesive joints: an engineering study
… The approach used is based on well known free volume theories. In the rubbery state, it is assumed that the transport kinetics is governed by the constant redistribution of the free volume, caused by the segmental motions of the polymeric chains. An expression for the diffusion coefficient …
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Residual stress in nanocrystalline nickel tungsten electrodeposits
… of equilibrium (unrelaxed) and contains excess free volume, in and of itself acting as the primary source of residual stress in these coatings. We show that the amount of free volume initially created in the films can be predicted from the pulse amplitude of the current waveform employed during …
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Rheology of molten polystyrene with dissolved gases
… the chain dilution effect and the addition of free volume. Rheological measurements and theoretical modeling are presented for molten polystyrene with dissolved gases, including carbon dioxide, 1,1-difluoroethane (R152a), and 1,1,1,2- tetrafluoroethane (Rl34a), which are considered to be …
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Transport and damage in hydrated coatings – a model soft active composite material
… interrelated fundamental processes – transport, volume change, stress, and damage – are present in active materials. This thesis explores the interconnection of these processes using water-based anti-corrosion coatings, water-absorbing polymer films composed of coalesced latex particles, as the …
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Application of Hansen Solubility Parameters and Thermomechanical Techniques to the Prediction of Miscibility of Amorphous Solid Dispersion. Investigating the role of cohesive energy and free volume to predict phase separation kinetics in hot-melt extruded amorphous solid dispersion using dynamic mechanical analyser, shear rheometer and solubility parameters data
Hot-melt extruded solid dispersion technique is increasingly employed to improve the solubility of poorly water-soluble drugs. The technique relies on the enhanced solubility of the amorphous form of the drug compared to its crystalline counterpart. These systems however are thermodynamically …
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Photochemical Applications to the Study of Complexity Phospholipid Bilayer Environments
… photochemistry enabled bilayer viscosity and free volume to be studied over a broad time scale. Spiropyrans/merocyanines with different polarity were synthesized by changing the substitution of the indole moiety enabling determination of the trans-membrane properties of the bilayer. In …
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Cell-walls of growing plant cells
… content of the wall and therefore the cell wall free volume directly influence wall extensibility. When hydration of A. xylinus cellulose composite pellicles was reduced using PEG 6000 solution and re-hydrated in buffer solution, followed by treatment with α-expansin or snail acetone powder …
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Post-Synthetic Chemical and Morphological Modifications of Polymer Membranes for Gas Separations
… packing of polymer segments, resulting in high free volume materials with good diffusion selectivity when processed into films. As a result of these characteristics, microporous polymers became potential candidates for next-generation gas separation membrane materials. Over the past two decades, …
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The effects of molecular orientation on the physical aging behavior of oriented glassy amorphous polymers
… rates were determined as a function of fusing volume and linear dilatometry, mechanical creep measurements, DSC, and tensile properties. The molecular state, including the free volume, of the oriented polymers was quantified using Positron Annihilation Lifetime Spectroscopy (PALS), oxygen …
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Physical and Gas Permeation Properties of a Series of Novel Hybrid Inorganic-Organic Composites Based on a Synthesized Fluorinated Polyimide
… which was attributed to an increase in free volume. The TEOS based hybrid materials had the largest decreases in permeability, while PTMOS based hybrid materials had performance in between these alkoxides. Decreased permeability for the TEOS based hybrids was attributed to the formation …
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Scalable Synthesis and Separation Performance of Covalent Organic Framework and Contorted Polyamide Membranes
… RO water desalination due to their increased free volume resulting from sterically hindered monomer structures. COF and contorted polyamide membranes show great promise for achieving superior permeability and selectivity compared to commercially available counterparts, but their industrial …
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