S. V. Shilov

Segmental orientation and mobility of ferroelectric liquid crystal polymers

IR spectroscopy was used to study the orientation and mobility of different molecular segments in a side chain ferroelectric liquid crystalline polymer (FLCP) in the book-shelf geometry. It was directly shown that the tilt angles for the mesogenic units and the spacers are different. The data obtained allowed us to construct a detailed model of segmental orientation in the SC phase for this FLCP. This model is consistent with the ‘zigzag’ model for tilted smectic phases. The rotational bias of carbonyl bonds is also confirmed and a possible orientation function for the carbonyl group is discussed. Time-resolved step-scan FTIR spectroscopy enabled us to follow the intra- and inter-molecular response of the FLCP to an external electric field with a time resolution of 5 mus. It was detected that mesogenic moiety, spacer and backbone take part in the reorientation process. The time responses of different molecular segments are similar on the time scale of a few hundred microseconds.

Reorientation behaviour of bent core molecules in response to an external electric field as detected by time-resolved FTIR spectroscopy

Time-resolved polarized Fourier transform infrared spectroscopy (FTIR) is employed to analyse the segmental orientation and mobility of achiral bent core molecules in response to an external electric field. By shearing the substance between ITO coated CaF2 windows two types of domain, racemic and homochiral, are formed in the high temperature B2 phase. Each of these domains is characterized by two spontaneous symmetry-breaking instabilities which yield a symmetric and an antisymmetric electro-optical response, respectively. Taking advantage of the specificity of IR spectroscopy, this switching behaviour is analysed on a molecular level for the moieties of the bent core liquid crystal materials. In this way, the electrically induced reorientation of the different segments on a cone and the suppression of the antiferroelectric structure at higher frequencies can be followed in detail. Furthermore the biased rotation of the two carbonyl groups around the molecular long axis is determined. It is shown that al...

Time-Resolved Polarized FTIR-Spectroscopy on the Molecular Structure and Mobility of Ferroelectric LC Elastomers (FLCE)

Abstract Time-resolved FTIR-spectroscopy is employed to study structure and mobility in ferroelectric LC polymers and elastomers (temperature range 20°C…130°C, dynamic range 0.1 Hz… 105 Hz). Due to its specifity the analysis of the (polarized) IR-spectra enables to determine the average orientation, the orientational order and the mobility in response to an electric field for the different molecular moieties (phenyl group, the polar groups, the methylene spacer and the polymer backbone). Furthermore the phase relationship in the motion of the different molecular groups can be extracted.

Segmental motion of ferroelectric liquid crystal polymer and elastomer during electro-optical switching

Application of both the conservative rapid scan and a novel step-scan Fourier-transform spectroscopy enables us to follow the intra- and intermolecular motion of ferroelectric liquid crystalline polymers and elastomers during electro- optical switching on a time scale from seconds down to microseconds. It has been detected that although all molecular parts move synchronously in course of the switching, the amplitude of such motions is different. The obtained results are discussed in terms of the role played by the molecular segments during the process of reorientation.

Structure and mobility in ferroelectric liquid crystalline elastomers as studied by time-resolved FTIR spectroscopy

Abstract The molecular structure and reorientation of ferroelectric liquid crystalline elastomers (FLCE) in response to an external electric field is studied on a microsecond scale with time-resolved Fourier transform infrared (FTIR) spectroscopy. In order to analyze the influence of the network on the molecular structure and mobility in FLCE, three similar FLC polysiloxanes are under study that differ just in their crosslinking architecture: besides the uncrosslinked polymer we obtain by photocrosslinking FLCE in which the backbones of either adjacent smectic layers (“interlayer”) or of the same smectic layer (“intralayer”) are preferably crosslinked. It is shown that the crosslinking leads to a slowing down of the molecular mobility which is stronger for the inter-than for the intralayer FLCE. Asymmetries in the reorientation times and/or in the reorientation angles are observed (elastic memory effect). The intralayer crosslinking causes a “locomotive effect”: the reorientation of the mesogenic cores precedes that ofthe backbones.

Time-Resolved Polarized FTIR-Spectroscopy on Structure and Mobility in Banana-Shaped Liquid Crystal Molecules

Abstract By use of time-resolved polarized Fourier-transform infrared (FTIR-) spectroscopy the molecular structure and mobility of B2 phase LC banana-shape molecules is investigated. Two samples are investigated: an achiral banana-shaped (B14) system and a mixture of achiral (B14) and chiral (B7*) banana-shaped molecules. The molecules are oriented by shearing the substance between ITO-coated CaF2 windows. The measurements give detailed information about a) the average orientation, b) the orientational order, c) the reorientation time, d) the reorientation angle and e) the phase relation between the different segments for the different molecular moieties. The experiments are performed in dependence on frequency and strength of the external electric field. The corresponding molecular response of the different moieties is recorded by means of step-scan FTIR spectroscopy with a time resolution of 5 microseconds.