TAILIEUCHUNG - Branched Polymers II Episode 4

Tham khảo tài liệu 'branched polymers ii episode 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Entangled Dynamics and Melt Flow of Branched Polymers Tom . McLeish1 Scott T. Milner2 1 IRC in Polymer Science and Technology Department of Physics and Astronomy University of Leeds Leeds LS2 9JT uK E-mail 2 Exxon Research and Enginering Company Route 22 East Annandale New Jersey 08801 USA One of the most puzzling properties of branched polymers is their unusual viscoelasticity in the melt state. We review the challenges set by both non-linear experiments in extension and shear of polydisperse branched melts and by the growing corpus of data on well-characterised melts of star- comb- and H- molecules. The remarkably successful extension of the de Gennes Doi-Edwards tube model to branched polymers is treated in some detail in the case of star polymers for which it is quantitatively accurate. We then apply it to more complex architectures and to blends of star-star and star-linear composition. Treating linear polymers as 2-arm stars for the early fluctuation-dominated stages of their stress-relaxation successfully accounts for the relaxation spectrum and viscosity-molecular weight relationship. The model may be generalised to strong flows in the form of molecular constitutive equations of a structure not found in the phenomenological literature. A model case study the pom-pom polymer exhibits strong simultaneous extension hardening and shear softening akin to commercial branched polymers. Computation with such a constitutive equation in a viscoelastic flow-solver reproduces the large corner vortices in contraction flows characteristic of branched melts and suggests possible future applications of the modelling tools developed to date. Keywords. Viscoelasticity Molecular rheology Branched polymers Tube model Non-New-tonian flow List of Symbols and Abbreviations. 197 1 Introduction. 199 Evidence for Topological Interaction . 199 The Tube Model . 201 2 Monodisperse Linear Polymers . 204 Reptation . 204 Expression for

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