Multi-walled carbon nanotubes (MWNTs) are a nanofiller that has desirable multifunctional properties. They have been shown to offer improved mechanical, thermal, and electrical properties in composites. Research has been studying their incorporation into polymer composites. Polyamide 12 is a polyamide of interest that has been manufactured to have lower moisture absorption and higher ductility than other commercial polyamides such as 6 and 6,6 at room temperature. In these studies, MWNTs have been incorporated into polyamide 12 at different weight loadings and using MWNTs with differing outer diameters. The composites were melt processed and characterized using differential scanning calorimetry (DSC) to understand the effects of MWNTs on the crystallization behavior of polyamide 12. A melt peak splitting behavior was observed in the polyamide 12 and composite samples when the specimens were not allowed to fully anneal. Total crystallinity in the samples remained the same between the polyamide 12 and composites when the samples were fully annealed. Total crystallinity increased by 1 to 4 percent in the composites over the polyamide 12 when samples were not fully annealed. The addition of MWNTs to the polyamide 12 system increased the amount of crystallization contained in the lower temperature melting peak. An increase in MWNT concentration resulted in an increase in the crystallinity contained in the lower temperature peak. The addition of smaller diameter MWNTs resulted in a further increase in the lower temperature peak when the outer diameter was below a critical size.

Reproduction de : Thèse de doctorat : Chimie des matériaux : Lyon 1 : 2006. / Titre provenant de l'écran titre. 290 réf. bibliogr.

Thesis (Ph.D.)--University of Delaware, 2009. / Principal faculty advisor: Chin-Pao Huang, Dept. of Civil & Environmental Engineering. Includes bibliographical references.

Thesis (Ph.D.)--Brown University, 2008. / Vita. Advisor : Jimmy M. Xu. Sciences copy 2 : includes supplementary digital materials. Written title on CD-ROM: Dan Straus thesis final version; Dan Straus thesis defense. Includes bibliographical references (leaves 111-123).

Thesis (M.S. in Applied Physics)--Naval Postgraduate School, December 2003. / Thesis advisor(s): Young W. Kwon, James H. Luscombe. Includes bibliographical references (p. 53-57). Also available online.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

Secondary electron (SE) emission from thin carbon foils induced by 1-20 keV positrons has been investigated over a range of nominal foil thicknesses from 1.0 to 5.0 μg/cm2. The measurement of SEs was carried out in forward geometry using a microchannel plate as a detector. The SE yield γ has been measured as a function of beam energy and compared with some Monte Carlo simulation results. We also present in this thesis the material parameter Λ=? / (dE / dx) and the emitted SE energy spectra. Forincident positron energy of 5 keV or higher, the distribution is found to be characterizedby the Sickafus form, AEm and m is close to 1. For low energy incident positrons however, another form, Bexp(E / t) , is proposed for describing the SE distribution. The maximum scattering angle for SEs emitted from 5.0 μg/cm2 is found to be around 60°. Measurements of energy loss and energy loss straggling for 1-10 keV positrons passing through thin carbon foils of different thicknesses ranging from 1.0 to 5.0 μg/cm2 are present in this thesis. The stopping power dE / dx and positron transmission coefficient have also been investigated as a function of incident positron energy and foil thickness. Particularly, our experimental results are compared with those from Monte Carlo simulation and theory with a view to providing a way to determine the real thickness of carbon foil. The ratio of the energy loss straggling to the foil thickness seems to have a linear relation with the beam energy. The transmitted positrons after passing through 5.0 μg/cm2 C-foil have a small scattering angle which is less than 10°. Titanium dioxide nanotube arrays fabricated by anodization of titanium foil and annealed at different temperatures were studied using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and positron annihilation spectroscopy (PAS). The crystallization process and morphological change of the nanotubes have been discussed. It is found that anatase (101) only appeared on the walls of the nanotube. The atomic concentration of fluoride and the ratio of Ti/O decreased when the annealing temperature increased. Vacancy type defects were found to diffuse toward the surface when the samples were annealed at 200°C and 400°C and healing of vacancies occurred at 600°C. In addition, the fluoride may form some complexes with vacancies on the surface hence lowering the value of the S parameter. A new design of the lifetime positron beam based on the SE emission is proposed. The observed experimental results and simulation results make it possible to construct a new type of high resolution (<250ps) lifetime positron beam. In addition, how rastering of the positron beam can be used to accurately locate the position of the C-foil is also shown; a feature that will be of value in setting up a positron lifetime system. Such a lifetime system is expected to be much simpler in construction than existing beam based lifetime spectroscopy systems. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

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