ISSN:1042-7147    

DOI:10.1002/pat.1992.220030501

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractWe have prepared several ferroelectric polysiloxanes with two and three benzenic ring moieties. The siloxane backbone is favorable to ferroelectric S *Cphase formation, and the chiral S *Cphase is observed in all of the polymers. Some of the spontaneous polarizations are very high, more than 100 nC/cm2(10−3C/m2) and the response times are less than 1 ms near the I‐S *Cor Sa–SS *Ctransition. Several binary mixtures between FLC copoly‐siloxanes and different low molar mass LC have been studied, and have shown the complete miscibility of these two components and richer mesomorphic sequences than for the polymers alone; for example, a

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030502

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractFerroelectric liquid crystalline polymers (FLCPs) were synthesized. These ferroelectricities were confirmed directly by measuring polarization reversal currents and other electro‐optical properties. The smectic layer structure of FLCP was also studied. A chevron structure similar to that of low molecular weight FLC was observed even in an FLCP cell; but the zigzag defects were not so sharp, which means that it is easy to obtain a good orientation even in large‐area displ

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030503

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThis 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 polarization

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030504

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractIn a liquid crystalline side chain polyacrylate containing one center of chirality in the terminal alkyl chain of the mesogenic part, switching times of 200–400 μs were measured in the SmC*phase. Below this phase an unidentified phase exists, which shows electroclinic‐like switching. The phase transition between those two phases can be shifted by applying an electric field.At higher molecular weights three subphases emerge in the SmC*region. Variation of the spacer length revealed, for the first time, ferroelectric switching even at a spacer length of only two CH2groups.By shifting the centre of chirality into the spacer of the side group a polymer resulted, which shows electroclinic switching in the SmC*phase, changing to ferroelectric switching when the voltage is increased.Incorporation of an oxirane ring as chiral building block into the spacer yielded a polymer that shows a sign inversion of the spontaneous polarization in the SmC*phase.A polymer containing a dioxolane carbonic ester as chiral unit exhibits three switching states, with the third state existing at a low or zero electric field. This phenomenon is known for antiferroelectric liquid crystals.By doping a racemic LC polymer with a chiral monomeric LC we induced a spontaneous polarization. Colored FLC polymers were obtained by two different approaches. In an FLC–dye copolymer, increasing switching speed in three different chiral smectic phases was observed when increasing the dye concent

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030505

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractWe demonstrate that ferroelectric liquid crystals dispersed in a polymer matrix can form uniaxially aligned elliptical droplets. The alignment is controlled by mechanical shear during the polymerization of a UV‐curable adhesive. The possibility of prealignment makes polymer‐dispersed ferroelectric liquid crystals suitable for application in flexible electro‐optical displays. In contrast to surface stabilized ferroelectric liquid crystal displays, the electro‐optical effect in our system is due to the deformed‐helix ferroelectric (DH

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030506

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractMeasurements of spontaneous polarization, tilt angle and response time on mixtures of a ferroelectric side chain polyacrylate with a low molecular mass liquid crystal of a very similar structure are reported. From the obtained values the rotational viscosity for the ferroelectric switching process is calculated. All mixtures exhibit an Arrhenius‐like temperature dependence of the rotational viscosity, the values for the polymer being three orders of magnitude higher than for the low molecular mass compoun

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030507

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractElectro‐optic and polarization reversal measurements were performed on a side‐chain polymer exhibiting a chiral smectic phase. Based on the observed electro‐optic and current responses, we discuss the possibility of an antiferroelectric structure in the polymer. In order to establish a model for the observed behavior, a detailed comparison with the properties of the low molar mass antiferroelectric substance MHPOBC was made. The birefringence modulation in the chiral smectic polymer, originating from the field‐induced antiferroelectric‐to‐ferroelectric transition, is analyzed for the case of a randomly oriented sample. The result shows that the coincidence of birefringence modulation and polarization current peaks is strong evidence for the existence of antiferroelectric order in the smectic layers. Such coincidence was observed both for MHPOBC and the chiral side‐chain

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030508

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractBroadband dielectric spectroscopy delivers in the frequency range from 10 Hz to 1010Hz 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 doesnotsplit 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‐ch

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030509

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe structure and phase behavior of liquid crystalline polymers (LCPs) having a common chiral side chain mesogen but different main chain structures have been investigated using small‐angle X‐ray scattering (SAXS). While the low molecular weight chiral side chain mesogen by itself exhibits ferroelectricity, the SAXS data of the side chain LCP with a flexible polyacrylate backbone contains a bilayered superstructure peak that is indicative of antiferroelectric order. The combined LCP with a nonpolar main chain mesogen also has a bilayered superstructure, but has a different structural organization in the proposed antiferroelectric phase compared to the side chain LCP. Further changes in the phase behavior and structural organization occur when a polar group is introduced into the main chain mesogen. A ferrielectric phase has been proposed to explain the observation of a trilayered superstructure in the corresponding SAXS data. The influence of the chemical structure and connectivity on the phase behavior and superstructure formation in the chiral LCPs is discus

ISSN:1042-7147    

DOI:10.1002/pat.1992.220030510

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY