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 27 for “"Reptation"”.
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Crack Healing in Polymers (Fracture, Reptation, Tack)
… t, temperature T, and molecular weight M. The reptation theory of self-diffusion in entangled polymers was used to describe chain motions and interpenetration at a polymer-polymer interface. Various dynamic quantities, including the average segment interpenetration depth (gamma), were related …
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Polymer Melts Investigated by Field Cycling NMR Relaxometry: From Simple Liquid to Reptation Dynamics
… non-entangled chains and the Doi/Edwards tube-reptation model for entangled polymers. Since 2004 a commercial relaxometer by Stelar has been operated in the Rössler group. Its capability to rapidly switch between different magnetic fields allows to measure the spin-lattice relaxation time in …
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Ft-Ir Study of the Dynamics of Entangled Polymer Melts
… infrared (FT-IR) spectroscopy. Based on the reptation model, the motion of a chain in the presence of topological entanglements is that of a one dimensional random walk along the chain contour. This motion allows the end portions of the chain to escape the initial oriented tube and form a new …
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Concentration profiles at amorphous polymer-polymer interfaces
… profiles are derived using the Rouse and reptation dynamics for the symmetric monodisperse and polydisperse interfaces, the asymmetric monodisperse interface, the symmetric blend interfaces, and the asymmetric interfaces of two different polymers. The profiles obtained are used to study …
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Long Chain Molecules in the Molten State: Surface Adsorption, Near Surface Structure, and Mutual-Diffusion
… time for a time scale much longer than the reptation time. It is speculated that the anomalous behavior is either due to small molecular residue in the sample or due to the long chain nature of the polymer itself. If the former possibility can be ruled out, the validity of applying the …
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Short-time interdiffusion at polymer interfaces: A probe to study polymer motion
… H reflected the diffusion of the chain ends. If reptation occurs, there would be a finite time, to, before which the chain centers do not cross the interface. Concentration profiles were measured with neutron reflectivity and secondary ions mass spectroscopy, up to the times of the order of the …
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Benchmark studies using quantum Monte Carlo: pressure estimators, energy, and entanglement
… the thesis, variational, diffusion, and reptation quantum Monte Carlo. Then we discuss the problem, trial wave function bias in the energy and other observables. Next we outline the Hamiltonians we are typically interested in for electronic systems and trial wave function forms used to …
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Dynamics of rod-coil block copolymers
… coil's tube presents entropic barriers to the reptation of the rod, modifying the unhindered motion of the coil along its tube into an activated reptation process. In the large rod limit where the coil is a perturbation on rod motion, the long rod cannot rotate around the surrounding …
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Microscopic theory for dynamics in entangled polymer nanocomposites
… and entangled needles can diffuse via a modified reptation dynamics over a window of polymer concentration but the compression of the tube and the blocking of the reptation motion must be accounted for. Generalization to treat mobile spheres is also possible and fully formulated.
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DYNAMICS AND COMPACTION OF CONGESTED AND/OR CONFINED DNA
… times agree with the relevant scaling laws for reptation dynamics indicateing coupled translational and rotational motion of DNA in the entangled regime. From a comparison of the MSD of cosmid DNA with that of colloid beads, an essential similarity is found indicating circular DNA molecules …
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Entwicklung und Charakterisierung thermotroper Polymerblends
… über Wasserstoffbrücken. Die Theorie der sticky reptation von Leibler erklärt die viskoelastischen Effekte ausgezeichnet. Dagegen bilden die HEMA-Gruppen im SH kaum intermolekulare H-Brücken, sondern liegen hauptsächlich intramolekular gebunden in einer zyklischen Konformation vor. <br>Sperrige …
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Polymer Structure and Dynamics in Nano-Confinements: Polymer Nanocomposiets and Cylindrical Confinement
… (Drep) in cylindrical confinement via the reptation model. The center-of-mass diffusion coefficients (DMSD) are also directly calculated from the mean-squared displacement in the diffusive regime, and are compared to Drep. At modest confinements, Drep agrees with DMSD, which suggests the …
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Energy and topology of heteropolymers
… that exists on time scales shorter than the reptation time. We then study the translocation of a polymer through a membrane. Our key finding is that the dynamics of translocation occur on the same time scale as diffusion, and are affected only weakly by the entropic barrier created by the …
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Multiscale simulation of viscoelastic flows : applications to kinetic theory models of polymer melts and liquid crystalline polymers
… for liquid crystalline polymer and a number of reptation models for polymer melts in different flow geometries.
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Molecular Modeling Studies of Dendrimers and Hyperbranched Polymers
… linear segments in the molecule exceeds 0.8. The reptation-based model proposed recently by Blackwell, Harlen and McLeish, for symmetric tree-like polymer melts is utilized to analyze the behavior of the linear-hyperbranched polymers in the entangled state. The average mass segments between branch …
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Monte Carlo simulations of amphiphilic systems.
… of its efficiency relative to both the classic reptation and CBMC for the simulation of chains lying on a lattice of high coordination number. A methodology for the simulation of polyoxyethylene oxide (POE) surfactants using a cubic lattice of coordination number c = 26 is briefly discussed.
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Development of improved aircraft de-icing fluids
… solutions. The model involves consideration of reptation, relaxation of the chains by slippage or loop relaxation, and normal Rouse dynamics is appropriately adapted to reflect the structural changes of the polymer molecules and the consequent pseudoplastic behaviour. The model has helped with …
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Effect of chain structure on the thermodynamics and kinetics of polymer crystallization
… all of the implications of the Hoffman-Miller reptation approach. Combination of this approach and the lattice-strain theory of Hoffman and Miller (which predicts curved face crystals) eliminates two of the major criticisms of the LH theory within a single theoretical framework. Through studies …
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The synthesis, stabilization and sintering of high performance semicrystalline polymeric powders
… developed by Wool. The latter is based on the reptation theory of de Gennes and Doi and Edwards. Sintering conditions were established which allowed for the attainment of comparable mechanical behavior to conventional processes.
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Direct imaging of single-walled carbon nanotubes reptational dynamics in packed-colloid porous media
… video microscopy to directly visualize the reptation and transport of intrinsically fluorescent, semiflexible, semiconducting single-walled carbon nanotubes (SWCNT) in the sub-micron pores of randomly packed colloids as fixed obstacles of packed-colloid porous media. In packed-colloid pores, …
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