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Surface and interface structure of diblock copolymer

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  1. Tez No: 401167
  2. Yazar: BÜLENT AKGÜN
  3. Danışmanlar: PROF. MARK D. FOSTER, PROF. WILLIAM J. BRITTAIN
  4. Tez Türü: Doktora
  5. Konular: Polimer Bilim ve Teknolojisi, Polymer Science and Technology
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2007
  8. Dil: İngilizce
  9. Üniversite: The University of Akron
  10. Enstitü: Yurtdışı Enstitü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 195

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Özet (Çeviri)

The main objective of the work presented in this thesis is to understand the surface and interface structure and dynamics of diblock copolymer brushes (DCBs). DCBs are stimuli-responsive materials and the surface properties of a DCB can be changed from those characteristic of one polymer block to those characteristic of the other one by treating the DCB with a solvent selective for one of its blocks. For this purpose, polystyrene-block-polyacrylate or polyacrylate-block-polystyrene brushes were synthesized using the“grafting from”technique in combination with atom transfer radical polymerization (ATRP). In the first part of this project the internal structure of DCBs after the synthesis and surface rearrangement were investigated using neutron reflectivity (NR) and grazing incidence small angle X-ray scattering (GISAXS). It was found that the internal brush structure depends strongly on the synthesis sequence of polymer blocks and the value of N. For small values of N (N  11), a model of two layers with an interfacial region of finite width provides a good description of the data. The interface width is found to be larger for DCBs which have the polymer block with the lower surface energy synthesized next to the substrate. A three layer model must be used to describe the structure of DCBs of larger N values (N  23) and of sufficiently asymmetric composition. The necessity of including a third layer is consistent with the presence of a lateral ordering of some type in the center of the brush, as evidenced by correlation peaks in the GISAXS data. The spacing of the in-plane ordering varies with the thickness of the poly(methyl acrylate) (PMA) block. After a DCB is treated with a selective solvent, Bragg rods appear in the GISAXS pattern. The appearance of Bragg rods indicates the formation of a new 2D structure which has a lateral spacing on the order of the total thickness of the brush. The Bragg rods disappear upon heating to 80 C. Roughness correlation between the interfaces of a DCB has been detected using longitudinal diffuse X-ray scattering and X-ray reflectivity. The amplitude of the fringes in the longitudinal diffuse scattering decreases with increasing thickness of the DCB, indicating that the interactions between substrate and brush surface decrease as the thickness of the DCB increases. Roughness correlation of the brush is observed after annealing the brush but, it is lost after the brush is swollen in the vapor of a nonselective solvent, dichloromethane. A remarkable suppression of polymer film surface fluctuations by the tethering of one end of each chain in a densely grafted brush has been demonstrated experimentally using X-ray Photon Correlation Spectroscopy (XPCS), a direct measure of dynamics. Within the range of time and length scale investigated, 0.2 s to 1100 s, and 200 nm to 5 m, no relaxation of the brush surface could be observed, even 170 C above the bulk glass transition temperature of corresponding untethered chains, suggesting that the surface relaxation time is increased by at least three orders of magnitude as compared to a film of untethered chains of comparable thickness. The observation of the suppression of long wavelength fluctuations on the surface of a dry homopolymer brush is consistent with theoretical predictions.

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