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INFLUENCE OF PRESSURE ON FAST DYNAMICS IN POLYMERS

Begen, Burak
http://rave.ohiolink.edu/etdc/view?acc_num=akron1195437587

Abstract Details

2007, Doctor of Philosophy, University of Akron, Polymer Science.
One of the biggest challenges in solid state physics today is understanding the nature of the glass transition. Dynamic studies are critical in solving some of the problems in the field. Until recently, investigations of dynamics in glass formers were mostly carried out as a function of temperature. However, with the advancements in experimental techniques and methods, the interest towards using pressure as an additional experimental variable increased. The advantages of pressure over temperature are two-fold: First, it only alters the density of the system, whereas temperature changes both the thermal energy and the density, and secondly, one can achieve significant density changes (~20%) with pressure, whereas temperature creates smaller density changes (~5%). These advantages let researchers make direct comparisons of the results with glass transition models (i.e. free volume ideas). The dynamics in the frequency range between 1 GHz and 5 THz (fast dynamics), are thought to have a crucial role. Crystals in this frequency range have a Debye-like density of vibrational states. Glasses, however, have two extra contributions when compared to crystalline structures: (i) an anharmonic relaxation-like contribution that appears as a quasielastic scattering (QES) and (ii) a harmonic vibrational contribution, which shows up as the boson peak (BP) in light and neutron scattering spectra. It has also been shown experimentally that fast dynamics in glasses are strongly correlated with the temperature dependence of structural relaxation.In this dissertation the influence of pressure on fast dynamics in polyisobutylene, polyisoprene and low molecular weight polystyrene is investigated using inelastic light, neutron and X-ray scattering techniques. The results are compared to the predictions of the existing models.The results for all polymers studied showed that the boson peak shifts more strongly than sound modes, suggesting that the variations cannot be fully described by the transformation of elastic continuum as has been claimed in a few recent publications. It is also observed that the boson peak intensity decreases significantly under pressure. However, when scaled to the Debye level, the boson peak intensity increases under pressure for all polymers. The analysis of the QES showed a strong decrease of intensity under pressure. These variations strongly correlate with the change in the boson peak intensity under pressure, suggesting a relationship between QES and BP.
Alexei Sokolov (Advisor)
182 p.
pressure; high pressure; high pressure cell; diamond anvil cell; DAC; polymers; fast dynamics; boson peak; quasielastic scattering

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Citations

  • Begen, B. (2007). INFLUENCE OF PRESSURE ON FAST DYNAMICS IN POLYMERS [Doctoral dissertation, University of Akron]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195437587

    APA Style (7th edition)

  • Begen, Burak. INFLUENCE OF PRESSURE ON FAST DYNAMICS IN POLYMERS. 2007. University of Akron, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=akron1195437587.

    MLA Style (8th edition)

  • Begen, Burak. "INFLUENCE OF PRESSURE ON FAST DYNAMICS IN POLYMERS." Doctoral dissertation, University of Akron, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1195437587

    Chicago Manual of Style (17th edition)

akron1195437587
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© 2007, all rights reserved.
This open access ETD is published by University of Akron and OhioLINK.