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Sökning: WFRF:(Ortegren J)

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1.
  • Ortegren, J., et al. (författare)
  • Dielectric relaxation of liquid crystalline dendrimers and liquid crystalline polymers with pendant nitro groups
  • 2001
  • Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:25, s. 10027-10033
  • Tidskriftsartikel (refereegranskat)abstract
    • The dielectric relaxation was determined in a time-domain spectrometer between 100 and 295 K and from 0.1 to 1000 Hz for series of dendritic liquid crystalline polymers with scaffolds based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) of generations 0-3 with 4-((R)-1-methylheptyloxy)phenyl 4-{4'-[10-(hydroxy-carbonyl)decyloxy]-phenyl} benzoate as mesogen and for the second generation of dendrimers with 4-[10-(hydroxycarbonyl)decyloxy]-biphenyl 4-[4'-(2-(R)-octyloxy)-3-nitrophenyl] benzoate as mesogen. Dielectric data are also reported for a side-chain liquid crystalline polymer based on {4''-[(R)-(-)-2-octyloxyl-3-nitro-phenyl 4-(4'-(11-acryloyl-oxyundecyloxy)phenyl}benzoate. The low temperature subglass process (gamma) assigned to the spacer group was essentially insensitive to molecular architecture and to the presence of a pendant nitro group in the mesogen. The high temperature sub-glass process (beta) assigned to a 180 degrees flip of part of mesogen was only moderately sensitive to the molecular architecture. The introduction of a pendant nitro group in the mesogen led to a substantial increase in both activation energy and relaxation strength. The results suggest that the phenylene ring with the pendant nitro group participates in the beta process.
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2.
  • Ortegren, J., et al. (författare)
  • Improved thermal stability of pyroelectric polymers by crosslinking of ferroelectric liquid crystals
  • 2001
  • Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1089-5647 .- 1520-6106 .- 1520-5207. ; 105:42, s. 10223-10227
  • Tidskriftsartikel (refereegranskat)abstract
    • Monofunctional ferroelectric liquid crystalline monomers and a blend of monofunctional/lbifunctional ferroelectric liquid crystalline monomers were photopolymerized, yielding a side-chain liquid crystalline polymer and a cross-linked polymer, respectively. The cross-linked polymer exhibited higher thermal stability than the side-chain liquid crystalline polymer and was pyroelectric up to 170 degreesC, whereas the side-chain liquid crystalline polymer lost most of its pyroelectricity at 38 degreesC. It is shown by electrooptic and birefringence measurements that cross-linking in the unwound SmC* phase prevented the reoccurrence of the helical superstructure.
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