References of "Lagerwall, Jan 50002154"
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See detailOn the coexistence of SmC* and SmCa* phases in binary chiral-dopant antiferroelectric mixtures
Lagerwall, Jan UL; Parghi, D. D.; Heppke, Gerd et al

in Ferroelectrics (2000), 244

We present the results from investigations on a series of binary chiral- dopant liquid-crystalline mixtures. The racemic host materials possess tilted smectic phases with varying strengths of synclinic ... [more ▼]

We present the results from investigations on a series of binary chiral- dopant liquid-crystalline mixtures. The racemic host materials possess tilted smectic phases with varying strengths of synclinic and anticlinic ordering (SmC and SmCalt phases respectively). The dopants used were either a strongly synclinic-favouring non liquid-crystalline chiral material (commonly used in FLC chiral-dopant mixtures) or a strongly anticlinic (antiferroelectric) material ((S)-MHPOBC). The electrooptic and dielectric properties of the mixtures were investigated in test cells of different thickness and the influence of each mixture component on the observed physical properties is discussed. [less ▲]

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See detailThe dependence on the helical pitch of the antiferroelectric dielectric modes
Lagerwall, Jan UL; Fütterer, T.; Moro, D. et al

in Ferroelectrics (1999), 244

In an attempt to determine the physical nature of the low-frequency dielectric mode in antiferroelectric liquid crystals, we have studied the dielectric response in thick planar-oriented samples of ... [more ▼]

In an attempt to determine the physical nature of the low-frequency dielectric mode in antiferroelectric liquid crystals, we have studied the dielectric response in thick planar-oriented samples of Smectic C/sub A/* compounds undergoing a helix inversion. If the mode is collective there ought to be a minimum in the dielectric absorption due to the mode, at the temperature at which the helical pitch diverges. Although the effect is not large, we find minima for both antiferroelectric modes at this point, indicating that both modes are related to the helical director structure. A corresponding experiment has also been performed on a binary mixture which shows a helix inversion for a certain mixing ratio. However, because the effect in this case is overshadowed by unavoidable variations in other parameters, no minimum was detected. [less ▲]

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See detailThe case of thresholdless antiferroelectricity: Polarization-stabilized twisted SmC* liquid crystals give V-shaped electro-optic response
Rudquist, Per; Lagerwall, Jan UL; Buivydas, M. et al

in Journal of Materials Chemistry (1999), 9(6), 1257-1261

We have studied the three-component liquid crystal mixture reported to exhibit ‘thresholdless antiferroelectricity’ [Inui et al., J. Mater. Chem, 1996, 6, 671]. We find that the thresholdless or V-shaped ... [more ▼]

We have studied the three-component liquid crystal mixture reported to exhibit ‘thresholdless antiferroelectricity’ [Inui et al., J. Mater. Chem, 1996, 6, 671]. We find that the thresholdless or V-shaped switching is obtained in thf absence of antiferroelectricity. This analog electro-optic response is due to the field-induced switching of a twisted smectic C* structure stabilized by polar surface interactions and by electrostatic bulk polarization charge interactions. The latter confine the director twist to thin surface regions leaving the bulk of the cell uniform, which gives good extinction at zero field. In sufficiently thin cells, such thresholdless switching can in fact be followed down to much lower temperatures, where the bulk would be antiferroelectric, but is maintained in the cells in the ferroelectric state by hysteresis from surface action. [less ▲]

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See detailElectrooptic and dielectric spectroscopy measurements of binary chiral-dopant antiferroelectric mixtures
Parghi, D. D.; Lagerwall, Jan UL; Heppke, Gerd

in Molecular Crystals and Liquid Crystals (1999), 351

Recent examinations on binary chiral-dopant antiferroelectric liquid crystalline mixtures revealed an unusual switching behaviour. In order to investigate the switching processes that take place in the ... [more ▼]

Recent examinations on binary chiral-dopant antiferroelectric liquid crystalline mixtures revealed an unusual switching behaviour. In order to investigate the switching processes that take place in the mixtures, both in the bulk and as influenced by surfaces, further electrooptic and dielec- tric spectroscopy studies have been carried out on two model binary mix- tures in the induced SmA*, SmC* and SmCA* phases. The dielectric spectra feature the different modes typical for these phases, but of varying purity, indicating a more complex phase behaviour than expected. The electrooptic behaviour in the antiferroelectric phase varied from clearly antiferroelectric to near hysteresis-free switching directly between ferro- electric states. We conclude that the phase sequence, and consequently switching behaviour, is a function of both the type of dopant used and of the strength of the surface interactions (cell thickness). In thin cells syn- clinic (ferroelectric) ordering appears to be favoured. [less ▲]

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