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Title: The very early stage of the crystallization of thin PET films studied by ellipsometry, AFM, and grazing incidence X-ray scattering
Author: Ibaragi, Masaharu
ISNI:       0000 0004 5922 1289
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2015
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Chapter 1 introduces the background and importance of this thesis. Poly (ethylene terephthalate) (PET) is one of the most important polymer materials for industrial fields because of the good properties caused by its crystallinity, especially, control the kinetics of crystallization is a key technology for the productivity. Therefore, it is very useful to investigate the kinetics and mechanism of PET crystallization in detail. Usually, studies of crystallisation have focused only on the bulk state, but the surface is important in many practical materials, and there is reason to suppose that the mechanisms and kinetics of crystallisation in bulk and surface may be very different. Chapter 2 described the methodologies and theories of the experiments used in this study, that is, the protocol behind making thin PET samples, and the measurements used to study them; ellipsometry, atomic force microscopy, and grazing incidence X-ray scattering. In Chapter 3, how to make good samples, that is, the improvement in the surface roughness of thin PET films, was described in detail. The difficulty of making thin PET film samples was shown by reference to the literature and my original data, and the procedure introduced dealt successfully with these problems by choosing good combinations of solvents and making samples under suitable condition. In Chapter 4, I turn to sample aging, that is, the period after the sample is made, which strongly influences the kinetics or effectiveness of the crystallization, especially in the early stage (the induction time). I hypothesised that this aging effect was caused by a relaxation related to molecule conformations, that is, the relaxation by annealing before crystallization, which should increase the trans conformation. This is similar to the order of the PET molecules in the crystal, so pre-ordering or nucleation should take place more easily after this conformational change. In Chapter 5, the major data of this study, obtained by GI-WAXS, ellipsometry, and AFM, are introduced. Before crystallization starts, there was an intermediate state, which was clearly different from both the amorphous and crystal states in the morphology. The size of this structure was around from 10 to 30 nm. This should be the pre-ordering present in thin PET film. The validity of results of measurements related to the pre-ordering and whether it detects the pre-ordering or not were discussed with the literature in Chapter 6. The length scale of the pre-ordering measured in this study was similar to the literature in which pre-ordering has previously been detected in bulk samples. And the influences of film thickness and annealing temperature were also discussed. Differences of crystallization and pre-ordering between bulk and thin films of PET with detailed data of kinetics were shown in Chapter 7. Basically, induction time and the crystal growth rate of thin films were longer and slower than those in the bulk as measured by ellipsometry. The explanation for this should be from the “thickness effect”. But effects due to the proximity to the free surface would emerge in thinner films, below 50 nm or so, and this could cause some interesting phenomenon because the surface effect is counter to the “thickness effect”.
Supervisor: Jones, Richard Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available