We develop a mesoscopic theoretical framework to study viscoelastic response of block copolymers in the vicinity of their order-disorder transition point. We use it to study orientation selection of lamellar phases of diblock copolymers under oscillatory shears. We examine the effect of hydrodynamics on the relaxation of lamellar phases, and include anisotropic viscous stresses that follow from the uniaxial nature of the phase. We also introduce network viscoelastic effects that model chain entanglements, also made consistent with the symmetry of the phase. A numerical algorithm has been developed to solve the governing equations, which has been implemented on a parallel computer architecture. Simple cases involving the relaxation of small transverse perturbations, or viscoelasticity arising from diffusive relaxation of the order parameter have been investigated, and used to validate the numerical code. We also address the issue of spontaneous orientation selection from an initially disordered state due to an imposed oscillatory shear. In the absence of hydrodynamic coupling, we observe that the so called parallel orientation is selected for small shear frequency and amplitude, crossing over to a perpendicular orientation at higher shear frequencies and amplitudes. Hydrodynamic effects are seen to shift this crossover region. We have also examined the effect of network entanglement at finite frequencies. We find that network entanglement can lead to faster alignment, and that anisotropic network stresses can significantly influence the orientation selection process. / Nous developpons un cadre theorique propre a l'echelle me oscopique dans le but d'etudier la reponse viscoelastique des blocs de copolymeres pres du point de transition entre leur etat ordonne et desordonne. Nous utilisons cette theorie pour e tudier la selection de l'orientation des phases de lamelles des blocs de copolymeres subissant des cisaillements oscillatoires. Nous examinons les effets hydrodynamiques de la relaxation des phases lamellaires et nous incluons les stress visqueux anisotropes, dues a la nature uniaxiale des phases. Nous introduisons aussi les effets viscoelastique relatifs aux r eseaux modelisant l'enchevetrement des chaines dans une approche consistante avec la symetrie des phases. Un algorithme nume rique sous implementation parallele a ete developpe pour resoudre les equations relatives a cette etude. Des cas simples impliquant la relaxation diffuse du parametre relatif a l'ordre ont ete examines et utilises pour verifier le code numerique. Nous adressons aussi la question de la selection de l'orientation spontane d'un etat initialement desordonne due a un cisaillement oscillatoire impose au systeme. Dans l'absence d'interaction hydrodynamique, nous observons que l'orientation denomme e parallele est selectionnee pour des petites frequences et amplitudes de cisaillement mais adopte une orientation perpendiculaire pour de grandes frequences et amplitudes de cisaillement. Les effets hydrodynamiques changent la region de transition. Nous avons aussi examin e l'effet d'enchevetrement du reseau pour des frequences finies. Nous trouvons que l'enchevetrement du reseau mene a un alignement plus rapide et que les stress des reseaux anisotropes peuvent influencer de maniere significative le processus de se lection d'orientation.
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.96823 |
| Date | January 2011 |
| Creators | Zhang, Xusheng |
| Contributors | Jorge Vinals (Internal/Supervisor) |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | French |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Physics) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | Electronically-submitted theses. |
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