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| Identifier |
uch.chemistry.msc//2004rousaki |
| Title |
Οι Επιμήκεις Νανοΐνες σε παροδικά δίκτυα πολυμερών όπως μελετήθηκαν με τη φασματοσκοπία συσχέτισης φωτονίων |
| Alternative Title |
Long Nanofibers in transient polymer networks as studied by photon correlation spectroscopy |
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Author
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Ρουσάκη, Αικατερίνη Α
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| Abstract |
Diblock copolymer chemistry allows the production of particles with designed persistent shape. In particular long cylindrical particles can be obtained by crosslinking a polyisoprene cylinder with polystyrene chains (Mw=7k) forming the coat. The supramolecular structure, with core diameter dPI=26.6nm and cylinder length Lw=1930nm can be isolated. Such a sample was synthesized and characterized from the laboratory of Prof. G. Liu in Calgary since the precursor diblock copolymer is the polystyrene-b-polyisoprene. We call the resulted assembly the PS-b-PI nanofiber. It is a diblock copolymer nanofiber consisting of crosslinked cylindrical core made of one block (polyisoprene) and surface anchored chains made of another block (polystyrene). We characterize the nanofibers in dilute equilibrated solutions with static and dynamic light scattering experiments. Dilute static light scattering experiments gave satisfactory results on size Rc and molecular weight per unit length Mu. We also obtained a quite good approximation of the persistent length lp, and verified a rod like overall shape from the profile of the scattering intensity. Dynamic light scattering experiments yielded a rather low value for the hydrodynamic radius compatible with the anisotropic shape of the nanofibers. In order to get an insight of the structure and diffusion of this long fibers in a chemically identical network of polystyrene homopolymers reflecting their adaptation as fillers, we have studied the physical state of these fibers in polystyrene solution for two molecular weights (Mw1=22.2kDa and Mw2=1.200kDa). Utilizing photon correlation spectroscopy two processes are clearly observed and unambiguously resolved. These were then attributed to the homopolymer and the nanofiber due to the vastly different inherent dynamics of the components of this molecular composite. At sufficienly low polystyrene concentrations a single particles behavior is observed, whereas for concentrations above the overlap polystyrene concentration C*, when a transient network is formed, nanofibers tend to aggregate. This was clearly witnessed by the intensity increase and the slowing down of the nanofibers diffusion. The interactions leading to the aggregation probably arise from an unbalanced osmotic pressure due to the excluded volume driven expulsion of polymers from the region between the particles. A depletion mechanism induces aggregation in concentrations greater than C*in both the low and the high molecular weight polystyrene in a good solvent cases.
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| Language |
Greek |
| Issue date |
2004-07-01 |
| Collection
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School/Department--School of Sciences and Engineering--Department of Chemistry--Post-graduate theses
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Type of Work--Post-graduate theses
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| Views |
154 |
Οι Επιμήκεις Νανοΐνες σε παροδικά δίκτυα πολυμερών όπως μελετήθηκαν με τη φασματοσκοπία συσχέτισης φωτονίων
