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  • 1
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 728-733 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The pyroelectric coefficient, the spontaneous polarization Ps, the optical tilt angle θ, and the switching time of a polysiloxane liquid crystalline polymer have been measured. The pyroelectric coefficient is found to be one order of magnitude greater and the response broader than for a low molar liquid crystal reported in the literature and is comparable to that of the solid ferroelectrics. Ps vs θ is found to be nonlinear, and the ratio of Ps/θ shows anomalies close to the SmC*-SmA transition temperature. The measurements of θ and the optical response time are used to calculate the switching time which spans from 1 to 100 ms, depending on the temperature. The optical response time in the SmA phase close to the SmC*-SmA transition temperature, together with a finite value of the pyroelectric coefficient, provide evidence of a SmC* phase induced by an external field. The rotational viscosity as a function of temperature shows critical behavior at the SmC*-SmA phase transition temperature.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 2
    Digitale Medien
    Digitale Medien
    Springer
    Colloid & polymer science 268 (1990), S. 222-229 
    ISSN: 1435-1536
    Schlagwort(e): Liquidcrystallinepolymers ; crosslinkedpolymers ; mechanicalproperties ; rubber-likeelasticity
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Abstract A liquid crystalline main-chain polymer was slightly crosslinked by a reaction withα, ω-difunctionalized oligo-siloxanes. Crosslinking does not disturb the liquid crystalline phases, which are identified by x-ray measurements as smecticB and smecticA phases. Measurements of the elastic properties of the crosslinked sample show rubber-like elasticity, even in the liquid crystalline phases. A difference of 7 K was found between cooling and heating for the smecticA/isotropic transition from DSC and mechanical measurements.
    Materialart: Digitale Medien
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  • 3
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 3 (1992), S. 249-255 
    ISSN: 1042-7147
    Schlagwort(e): Ferroelectric liquid crystals ; Polymers ; Dielectric spectroscopy ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: Broadband dielectric spectroscopy delivers in the frequency range from 10 Hz to 1010 Hz two collective dielectric loss processes (soft and Goldstone modes) and one molecular relaxation (β-relaxation). The soft mode and Goldstone mode are assigned to the fluctuation of the amplitude and the phase of the helical superstructure. The β-relaxation corresponds to the libration (hindered rotation) of the mesogene around its long molecular axis. At the SmA-SmC* phase transition this process does not split or broaden, and the temperature dependence of its relaxation rate does not show any deviation from an Arrhenius-like behavior. Its dielectric strength does not decline at the SmA-SmC* phase transition. These experimental findings are in contrast to the common explanation of the origin of the saturation polarization (“induced spontaneous polarization”), which is based on the existence of a “free” rotation inside the SmA phase and its strong hindrance in the ferroelectric SmC* phase. Furthermore, the high frequency results require a reformulation for the (generalized) Landau theory as applied to the SmA-SmC* phase transition. In comparing low molar mass and polymeric (elastomeric) FLC, the collective and molecular dynamics are qualitatively similar, independent of the molecular architecture (e.g. side-chain, combined main- and side-chain or crosslinked systems).
    Zusätzliches Material: 13 Ill.
    Materialart: Digitale Medien
    Bibliothek Standort Signatur Band/Heft/Jahr Verfügbarkeit
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  • 4
    Digitale Medien
    Digitale Medien
    New York, NY : Wiley-Blackwell
    Polymers for Advanced Technologies 3 (1992), S. 211-217 
    ISSN: 1042-7147
    Schlagwort(e): LC polymers ; LC elastomers ; Ferroelectricity ; Piezoelectricity ; Nonlinear optics ; Chemistry ; Polymer and Materials Science
    Quelle: Wiley InterScience Backfile Collection 1832-2000
    Thema: Chemie und Pharmazie , Maschinenbau
    Notizen: This paper describes the rational design and structure-property relations in three different types of polar LC polymers with interesting material properties, as follows. (i) Chiral LC polymers, which are functionalized with crosslinkable groups, can be converted into LC elastomers with chiral smectic C* phases. The mechanical orientability of these elastomers leads to new piezoelectric materials. (ii) The curing (dense crosslinking) of a polymer matrix provides one possibility of stabilizing the polar order of dye molecules, which is necessary for frequency doubling. Additionally, LC phases can help to stabilize this polar structure, which leads to large and stable nonlinear optical coefficients. (iii) Polymer analogous esterifications offer a convenient method for the synthesis of chiral smectic C* polymers with large ferrolectric polarizations.
    Zusätzliches Material: 6 Ill.
    Materialart: Digitale Medien
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