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  • 1
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Chemistry and Physics 199 (1998), S. 677-686 
    ISSN: 1022-1352
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: New director reorientation experiments with a series of different elastomers are presented. Elastomers with a permanent monodomain structure are stretched perpendicular to their initial director alignment. After a threshold strain is exceeded, stripe-domains are formed parallel to the external stress with alternating sense of rotation in each domain. With increasing network density the average spacing of the stripes decreases. The anisotropy of the polymer chains is varied both by changing the reduced temperature and by introducing smectic clusters via copolymerisation with a mesogen forming a smectic-A phase. The anisotropy of the network is analyzed by the isobaric expansion of the sample parallel to the director as a function of temperature. Reorientation experiments at different reduced temperatures show that the interval of strains, where the director rotates, depends on this anisotropy. The experiments on cybotactic-nematic elastomers reveal that smectic fluctuations give a significant contribution to the threshold. The results are compared to the theory of Warner and Terentjev, yielding a good qualitative agreement.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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  • 2
    Electronic Resource
    Electronic Resource
    Weinheim : Wiley-Blackwell
    Macromolecular Rapid Communications 16 (1995), S. 679-686 
    ISSN: 1022-1336
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology , Physics
    Notes: The strain-induced director reorientation process in nematic liquid single crystal elastomers is investigated for the case of an arbitrary angle between the original director and the external stress axis. If the mechanical stress is applied perpendicular to the original director axis, the reorientation process sets in at a threshold strain. The mesogens are realigning ‘clockwise’ or ‘counter-clockwise’ towards the axis of external stress, simultaniously the monodomain structure is distorted and a periodic pattern formation is observed. If the mechanical stress is applied obliquely with respect to the original director axis, a uniform director reorientation is obtained with retention of the monodomain structure. No threshold strain is observed for this process. The existence of a threshold strain in the case of a perpendicular arrangement of the director to the external stress axis can be understood as a consequence of the distortion of the monodomain structure.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    Library Location Call Number Volume/Issue/Year Availability
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