Browsing by Author "Kirkensgaard, JJK"

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    Complex structured polymers in extensional flow – rheology and small-angle neutron scattering
    (International Conference on Neutron Scattering, 2017-07-12) Mortensen, K; Kirkensgaard, JJK; Borger, A; Hassager, O; Almdal, K; Huang, Q; Dorokhin, A; Garvey, CJ
    Small-Angle Neutron Scattering are used to investigate stretched macromolecular fluid filaments to show how the extensional properties are related to the molecular architecture and properties. We have combined structural and rheological studies of a series of model polymers with different composition and architectures. The project entails synthesizing model polymer systems of specific architecture, subjecting these materials to controlled extensional flows and to measure the molecular deformation under controlled flow situation bySANS. We have targeted different systems: a ”simple\" sample of homogeneous high-molar mass polymers, where only the central part of a fraction of the polymers were D-labelled with the aim to highlight the polymer deformation and avoid influence of fast relaxation near the polymer ends [1]. Another example is a bimodal mixture of linear polymer chains with respectively high and low molar mass [2], and we have studied samples with more complex geometry, including 3-arm star architecture. The linear chains show typically 2D-SANS pattern with Lozenge shaped contour. The 3-arm star polymers show novel, unexpected correlations perpendicular to the flow axis. The structure and rheology are measured both as a function of strain flow velocity, final Hencky strain ratio and during the relaxation after cessation of extensional flow.
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    The tricontinuous 3ths(5) phase: a new morphology in copolymer melts
    (ACS Publications, 2014-10-23) Fischer, MG; de Campo, L; Kirkensgaard, JJK; Hyde, ST; Schröder-Turk, GE
    Self-assembly remains the most efficient route to the formation of ordered nanostructures, including the double gyroid network phase in diblock copolymers based on two intergrown network domains. Here we use self-consistent field theory to show that a tricontinuous structure with monoclinic symmetry, called 3ths(5), based on the intergrowth of three distorted ths nets, is an equilibrium phase of triblock star-copolymer melts when an extended molecular core is introduced. The introduction of the core enhances the role of chain stretching by enforcing larger structural length scales, thus destabilizing the hexagonal columnar phase in favor of morphologies with less packing frustration. This study further demonstrates that the introduction of molecular cores is a general concept for tuning the relative importance of entropic and enthalpic free energy contributions, hence providing a tool to stabilize an extended repertoire of self-assembled nanostructured materials. © 2014, American Chemical Society.