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The helical pitch formed by organic molecules, such as the α-helix of proteins, usually requires hydrogen bonding between chiral units and long-range positional order. It was recently found that certain liquid crystal oligomers can have a twist-bend nematic (NTB) phase with nanoscale heliconical structure without hydrogen bonding, molecular chirality or positional order. To understand the nature of this unique structure, here we present hard and resonant tender X-ray scattering studies of two novel sulfur containing dimer materials. We simultaneously measure the temperature dependences of the helical pitch and the correlation length of both the helical and positional order. In addition to an unexpected strong variation of the pitch with the length of the spacer connecting the monomer units, we find that at the transition to the NTB phase the positional correlation length drops. The helical structure was found not only in the NTB phase but observed even in the upper range of a smectic phase that forms just below the NTB state. The coexistence of smectic layering and the heliconical order indicates a layered (SmATB) phase wherein the rigid units of the dimers are tilted with respect to the smectic layer normal in order to accommodate the bent conformation of the dimers and the tilt direction rotates along the heliconical axis.

Circularly polarized luminescent (CPL) materials have garnered considerable interest for a variety of advanced optical applications including 3D imaging, data encryption, and asymmetric catalysis. However, the development of high-performance CPL has been hindered by the absence of simple synthetic methods for chiral luminescent emitters that exhibit both high quantum yields and dissymmetry factors. In this study, we present an innovative approach for the synthesis of macro-chiral liquid crystal quantum dots (Ch-QDs/LC) and their CPL performance enhancement through doping with 4-cyano-4'-pentylbiphenyl (5CB), thus yielding a CPL-emitting generator (CEG). The Ch-QDs/LCs were synthesized, and their surfaces functionalized with a chiral mesogenic ligand, specifically cholesteryl benzoate, anchored via a lipoic acid linker. Under the regulation of chiral 2S-Zn 2+ coordination complexes, the chiral LC encapsulation process promotes coordinated ligand substitution, resulting in an exceptional quantum yield of 56.3%. This is accompanied by high absorption dissymmetry factor ( g abs ) and luminescence dissymmetry factor ( g lum ) values ranging from 10 -3 to 10 -2 , surpassing most reported dissymmetry factors by at least an order of magnitude. The modular Ch-QDs/LCs demonstrate the ability to transfer chirality to the surrounding medium efficiently and manifest macro-chiral characteristics within a nematic LC matrix. Utilizing Ch-QDs/LC as an effective CPL emitter within achiral 5CB matrices enabled the system to achieve a maximum g lum value of 0.35. The resultant CEG device acted as a direct CPL source, initiating enantioselective photopolymerization.

The idea that rodlike molecules possessing an electric dipole moment could exhibit a ferroelectric nematic phase was suggested more than a century ago. However, only recently such a phase has been reported for two quite different liquid crystals: RM734 [4-[(4-nitrophenoxy)carbonyl)]phenyl 2,4-dimethoxybenzoate] and DIO [2.3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl 2.6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate]. For RM734 a direct ferroelectric nematic (N_{F}) to classical nematic N transition was reported, whereas for DIO an intermediate phase N_{x} was discovered between the N_{F} and the N phases. Here we present high-resolution calorimetric evidence that an intermediate N_{x} phase also exists in RM734 along a narrow temperature range between the N_{F} and the N phases.

We present a comparative study of the optical and dielectric anisotropy of a laterally fluorinated liquid crystal dimer and its homologous trimer, both exhibiting two nematic phases. In the high-temperature nematic phase, both oligomers exhibit positive optical anisotropy with similar magnitude, which, however, is lower in comparison with the optical anisotropy of the monomer. In the same temperature range, the dielectric permittivity along and perpendicular to the nematic director, measured on magnetically aligned samples, reveals negative dielectric anisotropy for both oligomers, which saturates as the temperature approaches the N-N phase transition temperature. Comparison of the dielectric anisotropies of the oligomers with the corresponding anisotropy of the monomer indicates a systematic variation of its magnitude with the number of the linked mesogenic units. Results are compared with the corresponding anisotropies of the cyanobiphenyl dimers, the archetypal compounds with two nematic phases, and are discussed in terms of the dipolar structure of the mesogens and the dipolar correlations in their nematic phases.

We report on the temperature dependence of birefringence and of the static dielectric permittivity tensor in a series of binary mixtures between the symmetric, bent-shaped, 1'',9''-bis(4-cyanobiphenyl-4'-yl)nonane (CB9CB) dimer and the monomeric nematogen 5CB. In the studied composition range the mixtures exhibit two nematic phases with distinct birefringence and dielectric features. Birefringence measurements are used to estimate the temperature dependence of the tilt between the axis defining the nanoscale helical modulation of the low temperature nematic phase with the (local) direction of the maximal alignment of the cyanobiphenyl units. Planar as well as magnetically and/or electrically aligned samples are used to measure the perpendicular and parallel components of the dielectric permittivity in both nematic phases. A self-consistent molecular field theory that takes into account flexibility and symmetry of the constituent mesogens is introduced for the calculation of order parameters and intra-molecular orientational dipolar correlations of the flexible dimers as a function of temperature/concentration. Utilising the tilt angle, as calculated from the birefringence measurements, and the predictions of the molecular theory, dielectric permittivity is modelled in the framework of the anisotropic version of the Kirkwood-Fröhlich theory. Using the inter-molecular Kirkwood correlation factors as adjustable parameters, excellent agreement between theory and permittivity measurements across the whole temperature range and composition of the mixtures is obtained. The importance of the orientational, intra- and inter-molecular, dipolar correlations, their relative impact on the static dielectric properties, as well as their connection with the local structure of the nematic phases of bent-shaped bimesogens, is discussed.

An achiral compound, DIO, known to exhibit three nematic phases namely N, N X and N F , is studied by polarizing microscopy and electro-optics for different surface conditions in confinement. The high temperature N phase assigned initially as a conventional nematic phase, shows two additional unusual features: the optical activity and the linear electro-optic response related to the polar nature of this phase. An appearance of chiral domains is explained by the spontaneous symmetry breaking arising from the saddle-splay elasticity and followed by the formation of helical domains of the opposite chirality. This is the first example of helical segregation observed in calamitic non-chiral molecules in the nematic phase. As reported previously, the ferronematic N F shows strong polar azimuthal surface interaction energy which stabilizes a homogeneous structure in planar aligned LC cells rubbed parallel and exhibits a twisted structure in cells with antiparallel buffing. The transmission spectra are simulated using Berreman's 4 × 4 matrix method. The observed agreement between the experimental and the simulated spectra quantitatively confirms the presence of twisted structures in antiparallel rubbed cells.

The correlation between the size of nanoparticles, the structure and shape of mesogenic ligands and the ensuing assembly behaviour is not really understood. Closer inspection shows very surprising features. Here, 2- and 4-nm gold nanoparticles (NPs) were synthesized, and grafted with a forked ligand containing two rod-like mesogens in its branches: one cholesterol, the other with azobenzene. The 4-nm NPs also contained n-hexylthiol as co-ligand. They were found to form a FCC cubic superlattice, whereas the 2-nm NPs form hexagonal HCP with weak birefringence, hence with partially oriented ligands. The structures were compared with those of related systems containing a range of different azobenzene-to-cholesterol ratios, all giving body-centred tetragonal superlattices with various degrees of anisotropy. Geometric analysis is presented in terms of the asphericity of the NPs' surroundings, requirement for space-filling and structural anisotropy. Some general rules are derived to help design the soft corona around the NPs in order to obtain superlattices with the desired structure and anisotropy., (© 2022 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

High-resolution calorimetry has played a significant role in providing detailed information on phase transitions in liquid crystals. In particular, adiabatic scanning calorimetry (ASC), capable of providing simultaneous information on the temperature dependence of the specific enthalpy h(T) and on the specific heat capacity c_{p}(T), has proven to be an important tool to determine the order of transitions and render high-resolution information on pretransitional thermal behavior. Here we report on ASC results on the compound 2,3',4',5'-tetrafluoro[1,1'-biphenyl]-4-yl 2,6-difluoro-4-(5-propyl-1,3-dioxan-2-yl) benzoate (DIO) and on mixtures with 4-[(4-nitrophenoxy)carbonyl]phenyl 2,4-dimethoxybenzoate (RM734). Both compounds exhibit a low-temperature ferroelectric nematic phase (N_{F}) and a high-temperature paraelectric nematic phase (N). However, in DIO these two phases are separated by an intermediate phase (N_{x}). From the detailed data of h(T) and c_{p}(T), we found that the intermediate phase was present in all the mixtures over the complete composition range, albeit with strongly decreasing temperature width for that phase with decreasing mole fraction of DIO (x_{DIO}). The x_{DIO} dependence on the transition temperatures for both transitions could be well described by a quadratic function. Both these transitions were weakly first order. The true latent heat of the N_{x}-N transition of DIO was as low as L=0.0075±0.0005J/g and L=0.23±0.03J/g for the N_{F}-N_{x} transition, which is about twice the previously reported value of 0.115 J/g for the N_{F}-N transition in RM734. In the mixtures both transition latent heats decrease gradually with decreasing x_{DIO}. At all the N_{x}-N transitions pretransition fluctuation effects are absent and these transitions are purely but very weakly first order. As in RM734 the transition from the N_{F} to the higher-temperature phase exhibits substantial pretransitional behavior, in particular, in the high-temperature phase. Power-law analysis of c_{p}(T) resulted in an effective critical exponent α=0.88±0.1 for DIO and this value decreased in the mixtures with decreasing x_{DIO} toward α=0.50±0.05 reported for RM734. Ideal mixture analysis of the phase diagram was consistent with ideal mixture behavior provided the total transition enthalpy change was used in the analysis.

Polarized beam infrared (IR) spectroscopy provides valuable information on changes in the orientation of samples in nematic phases, especially on the role of intermolecular interactions in forming the periodically modulated twist-bent phase. Infrared absorbance measurements and quantum chemistry calculations based on the density functional theory (DFT) were performed to investigate the structure and how the molecules interact in the nematic (N) and twist-bend (N TB ) phases of thioether dimers. The nematic twist-bend phase observed significant changes in the mean IR absorbance. On cooling, the transition from the N phase to the N TB phase was found to be accompanied by a marked decrease in absorbance for longitudinal dipoles. Then, with further cooling, the absorbance of the transverse dipoles increased, indicating that transverse dipoles became correlated in parallel. To investigate the influence of the closest neighbors, DFT calculations were performed. As a result of the optimization of the molecular cores system, we observed changes in the square of the transition dipoles, which well corresponds to absorbance changes observed in the IR spectra. Interactions of molecules dominated by pairing were observed, as well as the axial shift of the core to each other.

Infrared spectroscopy (IR) and quantum chemistry calculations that are based on the density functional theory (DFT) have been used to study the structure and molecular interactions of the nematic and twist-bend phases of thioether-linked dimers. Infrared absorbance measurements were conducted in a polarized beam for a homogeneously aligned sample in order to obtain more details about the orientation of the vibrational transition dipole moments. The distributions to investigate the structure and conformation of the molecule dihedral angle were calculated. The calculated spectrum was compared with the experimental infrared spectra and as a result, detailed vibrational assignments are reported.

We present dynamic time-resolved measurements of a multi-pixel analog liquid crystal phase modulator driven at a 1 kHz frame rate. A heterodyne interferometer is used to interrogate two pixels independently and simultaneously, to deconvolve phase modulation with a wide bandwidth. The root mean squared optical phase error within a 30 Hz to 25 kHz bandwidth is <0.5° and the crosstalk rejection is 50 dB. Measurements are shown for a custom-built device with a flexoelectro-optic chiral nematic liquid crystal. However, the technique is applicable to many different types of optical phase modulators and spatial light modulators.

We report the formation of a 3D body-centred self-assembled superlattice of gold nanoparticles whose interparticle gap, and hence its plasmonic properties, are adjustable exclusively in the xy-plane. Thus, even though the particles are spherical, their anisotropic packing generates tailorable plasmonic dichroism. The gold nanoparticles are coated with forked ligands containing two mesogens: either two cholesterols ("twin"), one cholesterol and one azobenzene ("Janus"), or a mixture of the two. Beside the body-centered arrangement of gold nanoparticles, the structure also contains unusual two-dimensionally x-y dual undulated (eggbox-like) smectic-like layers of mesogens. Moreover, the presence of azobenzene mesogens allows the superlattice to be melted through UV-induced photo-isomerization; the process is reversible displaying low fatigue on repeated cycling., (© 2022 Wiley-VCH GmbH.)

Fourier-transform infrared polarized spectroscopy was employed, to obtain the three components of the infrared absorbance for a series of bent-shaped dimers containing double fluorinated terphenyl core (DTC5Cn, n = 5, 7, 9, 11). The data were used to calculate both uniaxial and biaxial order parameters, for various molecular groups of dimers. The molecule bend was estimated based on the observed differences between the uniaxial order parameters for the terphenyl core and central hydrocarbon linker. The orientational order, distinctly reverses its monotonic trend of increase to decrease at the transition temperature, from the uniaxial nematic to the twist-bend nematic phase as result of the director tilt in latter/(twist-bend) phase. The molecular biaxiality, which is negligible in the nematic phase, starts increasing on entering the twist-bend nematic phase, following a sin-square relationships with the tilt angle. The local director curvature is found to be controlled by the molecular biaxiality parameter.

The discovery of electrochemical switching of the L α phase of chlorpromazine hydrochloride in water is reported. The phase is characterized using polarizing microscopy, X-ray scattering, rheological measurements, and microelectrode voltammetry. Fast, heterogeneous oxidation of the lyotropic liquid crystal is shown to cause a phase change resulting from the disordering of the structural order in a stepwise process. The underlying molecular dynamics is considered to be a cooperative effect of both increasing electrostatic interactions and an unfolding of the monomers from "butterfly"-shaped in the reduced form to planar in the oxidized form., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)

The understanding of the relationship between molecular structure and the formation of the nematic twist-bend phase is still at an early stage of development. This is mainly related to molecular geometry, while the correlation between the nematic twist-bend phase and the electronic structure is ambiguous. To explore the electronic effect on properties and stabilization of the nematic twist-bend phase we investigated 2',3'-difluoro-4,4''-dipentyl- p -terphenyl dimers (DTC5C n ). We used polarized fourier transform infrared spectroscopy, which can, at least in principle, provide information about the ordering in the twist-bend phase. All dimers show a significant drop in the average value of the transition dipole moment for parallel dipoles at the transition from the nematic to the twist-bend phase, and an increase for perpendicular dipoles, despite remaining unchanged for the monomer. Density functional theory calculations were used to determine the geometric and electronic properties of the hydrogen bonded complexes. We have provided experimental and theoretical evidence of stabilization of the nematic twist-bend phase by arrays of multiple hydrogen bonds (XF⋯HX, X-benzene ring)., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Gold nanoparticles (AuNPs) have been prepared and surface-functionalized with a mixture of 1-hexanethiol co-ligands and chiral discogen ligands separated from a disulfide function via a flexible spacer. Polarized optical microscopy together with differential scanning calorimetry showed that the organic corona of the nanocomposite forms a stable chiral discotic nematic phase with a wide thermal range. Synchrotron X-ray diffraction showed that gold NPs form a superlattice with p 2 plane symmetry. Analysis indicated that the organic corona takes up the shape of a flexible macrodisk. Synchrotron radiation-based circular dichroism signals of thin films are significantly enhanced on the isotropic-LC transition, in line with the formation of a chiral nematic phase of the organic corona. At lower temperatures the appearance of CD signals at longer wavelengths is associated with the chiral organisation of the NPs and is indicative of the formation of a second helical structure. The decreased volume required and the chiral environment of the disc ligands drives the nanoparticles into columns that arrange helically, parallel to the shortest axis of the two dimensional lattice., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We have solved the long-standing problems of stability and hysteresis, and we are able to obtain the homogeneous uniform lying helix structure in polymer-free cholesteric liquid crystals. This is instrumental for the present work to demonstrate the analog modulation at high speed and high precision. The device is configured for the transverse field switching wherein the substrate surface is flat. In addition to the response time of 10 ms at room temperature, we have obtained the R-squared and the adjusted R-squared as a measure of true sine wave for the sinusoidal responding transmissions from 1 Hz to 100 kHz that are all greater than 0.9993. In a Michelson interferometer, the phase shift at wavelength 633 nm after two passes has been measured to be equal to about $\pi /{9}$π/9 at 4.6 V/µm for the chiral-doped nematic mixtures E7.

The dielectric spectra of the twist-bend nematic phase (NTB) of (the bent-shaped) achiral liquid-crystal dimer 1''-,7''-bis(4-cyanobiphenyl-4'-yl)heptane (CB7CB) are studied for the determination of the different relaxation modes. Two molecular processes and one collective process were observed in the megahertz frequency range. Two molecular processes were assigned: one to the precessional rotation of the longitudinal components of the cyanobiphenyl groups and the second one to the spinning rotation of the transverse component of the CB7CB dimer. The peak, at a frequency of about 1 MHz, shows a peculiar temperature behavior at the NTB to N transition, reminiscent of the soft mode at the transition from the SmA to the SmC phase. This peak can be assigned to a collective fluctuation of the tilt angle of the coarse grained director N with respect to the pseudo-layer normal. This corresponds well with the electro-clinic effect observed as a response to an electric field in electro-optic experiments. The low frequency relaxation process, observed in the frequency range of 1 Hz-102 Hz can be identified as a Goldstone mode, related to long-scale fluctuation of the cone phase. The frequency drop of the mode on increasing the bias field is interpreted as unwinding of a helix and an indication of the formation of a field induced nematic splay bend phase (NSB). This finding is also confirmed by birefringence data in the presence of strong bias fields.

Wide band dielectric spectroscopy of bent-shaped achiral liquid-crystal dimers 1″-n″-bis(4-cyanobiphenyl-4'-yl) n-alkanes (CBnCB n = 7, 9, 11) has been investigated in a frequency range 0.1 Hz-100 MHz using planar-aligned cells of sample thicknesses ranging from 2 to 10 (μm) over a temperature range that covers both nematic and twist bend nematic phases. Two peaks in the dielectric spectrum in the higher frequency range are assigned to the molecular relaxation processes. The peak at the highest frequency, ∼40 to 80 MHz, is assigned to an internal precessional rotation of a single unit of the dimer around the director. The mode in the next lower frequency range of 2-10 MHz is assigned to the spinning rotation of the dimer around its long axis. This involves fluctuations of the dipole moment of the bent-shaped conformation that is directed along its arrow direction of the bow shape formed by the dimer. The peak in the frequency range 100 kHz-1 MHz can be assigned to the collective fluctuations of the local director with reference to the helical axis of the N TB structure. The dependence of its frequency on temperature is reminiscent of the soft mode observed at the SmA * to SmC * phase transition. This result clearly corresponds to the electro-clinic effect-the response of the director to the applied electric field in an electro-optic experiment. The lowest frequency mode, observed in the frequency range of 0.1 Hz-100 Hz, is identified with the Goldstone mode. This mode is concerned with the long range azimuthal angle fluctuations of the local director. This leads to an alternating compression and expansion of the periodic structure of the N TB phase.

We report dynamic light scattering measurements of the orientational (Frank) elastic constants and associated viscosities among a homologous series of a liquid crystalline dimer, trimer, and tetramer exhibiting a uniaxial nematic (N) to twist-bend nematic (N TB ) phase transition. The elastic constants for director splay (K 11 ), twist (K 22 ) and bend (K 33 ) exhibit the relations K 11 > K 22 > K 33 and K 11 /K 22 > 2 over the bulk of the N phase. Their behavior near the N-N TB transition shows dependency on the parity of the number (n) of the rigid mesomorphic units in the flexible n-mers. Namely, the bend constant K 33 in the dimer and tetramer turns upward and starts increasing close to the transition, following a monotonic decrease through most of the N phases. In contrast, K 33 for the trimer flattens off just above the transition and shows no pretransitional enhancement. The twist constant K 22 increases pretransitionally in both even and odd n-mers, but more weakly so in the trimer, while K 11 increases steadily on cooling without evidence of pretransitional behavior in any n-mer. The viscosities associated with pure splay, twist-dominated twist-bend, and pure bend fluctuations in the N phase are comparable in magnitude to those of rod-like monomers. All three viscosities increase with decreasing temperature, but the bend viscosity in particular grows sharply near the N-N TB transition. The N-N TB pretransitional behavior is shown to be in qualitative agreement with the predictions of a coarse-grained theory, which models the N TB phase as a "pseudo-layered" structure with the symmetry (but not the mass density wave) of a smectic-A* phase.

We present here the first time-resolved tilt-angle and retardance measurements for large-tilt (>45°) flexoelectro-optic liquid crystal modulators. These devices have potential for next generation fast switching (>1 kHz), 0-2π analog phase spatial light modulators (SLMs), with applications in optical beamsteering, microscopy and micromachining. The chiral nematic device used consisted of a mixture of CBC7CB and the chiral dopant R5011 in a nominally 5 µm-thick cell, aligned in the uniform lying helix mode. As the device is dynamically switched over angles of ± 54°, retardance changes of up to 0.17λ are observed. Furthermore, the time-resolved measurements reveal an asymmetry in the tilt in the optic-axis depending on the polarity of the applied electric field. The change in the optic-axis exhibits a pattern dependence, whereby it is determined by both the pulse history and the applied field. This pattern dependence results in tilt-angle errors of up to 8.8°, which could manifest as phase errors as large as 35.2° in potential SLMs. These time domain measurements may allow correction of these deterministic errors, to realize practical devices.

In this paper, we demonstrate a flexoelectro-optic liquid crystal phase-only device that uses a chiral nematic reflector to achieve full 2π phase modulation. This configuration is found to be very tolerant to imperfections in the chiral nematic reflector provided that the flexoelectro-optic LC layer fulfils the half-wave condition. Encouragingly, the modulation in the phase, which operates at kHz frame rates, is also accompanied by low amplitude modulation. The configuration demonstrated herein is particularly promising for the development of next-generation liquid crystal on silicon spatial light modulators.

Molecular order and dynamics of the CB-C9-CB liquid crystalline dimer exhibiting the nematic (N) and the twist bend nematic (Ntb) phases were investigated by proton NMR spectroscopy, using fields of 0.78 T and 7.04 T, and relaxometry. The first relaxometry experiments for a very wide Larmor frequency domain (8 kHz-300 MHz) on this system, using a combination of standard and fast field cycling NMR techniques, were performed. The spectroscopy results in the Ntb phase allowed us to probe the local molecular orientation relative to the Ntb helix axis. The relaxation data were analyzed considering order director fluctuations (ODF), molecular self-diffusion (SD) and local molecular rotations/reorientations (R) relaxation mechanisms. Global fits of theoretical relaxation models, as a function of temperature and Larmor frequency, for the phases under investigation, allowed for the determination of rotational correlation times, diffusion coefficients, viscoelastic parameters, correlation lengths and activation energies (in the case of thermally activated mechanisms). A clear difference between the structures of the N and Ntb phases was detected from the results of proton spin-lattice relaxation through distinct temperature and frequency dependencies' signatures of the collective modes. Significant pre-transitional effects were observed at the N-Ntb phase transition both from relaxometry and spectroscopy data. The experimental results correlate to data and models for comparable liquid crystalline systems.

Using proton and deuterium NMR spectroscopy, this work provides a description of the molecular orientational order of the mesogenic groups in both the N tb and the classical nematic phase (N) of the liquid crystal dimer CB-C9-CB. The proton NMR data were collected at high field (7 T) with the nematic domains aligned by the field. Deuterium NMR data obtained from aligned samples at 11.7 T, published by Hoffmann , A. Soft Matter 2015 , 11 , 850 , were also considered in this study. Using the first-order perturbation theory, we carried out detailed simulations of the proton spectra from the terminal mesogenic groups along with the quadrupolar splittings from the carbon-deuterium bonds in the first chain positions, which allow for the determination of the Saupe order tensor for the mesogenic groups. We show that the main mechanism that induces the change of the 1 H NMR spectrum and the quadrupolar splittings at the N-N tb phase transition is the change of the orientation of the most ordered molecular frame (eigenframe of the Saupe tensor), along with the onset of the molecular biaxiality parameter, D. This orientation change is associated with the achiral symmetry breaking at the N-N tb phase transition.

A modulated and conventional DSC study of the transitions between the twist-bend nematic (Ntb), regular nematic (N) and isotropic liquid (Iso) phases was performed on a series of difluoroterphenyl-based dimers with (CH2)n spacers; n = 5, 7, 9, 11. The enthalpy of Ntb-N transition decreases steeply with increasing n, while that of the N-Iso transition increases with n; hence, the greatest effect of increasing n is a lowering N phase enthalpy. Based on past and present X-ray scattering experiments, we estimate the average molecular conformation in the Ntb phase and perform torsion energy calculations on the spacer. From this, the lowering enthalpy of the N phase is attributed to the decreasing torsional energy cost of bringing the two terphenyls from an inclined twisted conformation in the Ntb phase, to almost parallel in the N phase. With increasing n the C-C bonds of the spacers twist less away from their trans conformation, thereby reducing the overall torsion energy of the N phase. It is speculated that the nearly continuous nature of the Ntb-N transition in n = 11 dimer is associated with the divergence of the helical pitch toward infinity which is intercepted by a final jump at the very weak (0.01 J g-1) first-order transition. Small-angle X-ray scattering results suggest similar local cybotactic layering in both nematic phases, with four sublayers, i.e. tails, mesogens, spacers, mesogens.

We present a flexoelectro-optic liquid crystal (LC) analog phase modulator with >2π phase range at a 1 kHz switching frequency. The chiral nematic LC mixture consists of the bimesogen CBC7CB with chiral dopant R5011, aligned in the uniform lying helix mode. The mixture exhibits >±π/4 rotation of the optic axis for a drive voltage of ±21.5  V (E=±4.5  V μm -1 ). The rotation of the optic axis is converted into a phase modulation with the aid of a reflective device configuration incorporating a ∼5  μm LC cell, a polarizer, two quarter-wave plates, and a mirror. The residual amplitude modulation is found to be <23%. This flexoelectro-optic phase modulator combination has the potential to enable analog spatial light modulators with very fast frame rates suitable for a range of applications.

2D supramolecular organization of a series of six cyanobiphenyls bimesogens deposited on highly oriented pyrolytic graphite (HOPG) is studied by scanning tunneling microscopy (STM). The adsorbates are 1,ω-bis(4-cyanobiphenyl-4'-yl)alkanes (CBnCB) with different lengths of their flexible alkyl spacer (containing from 7 to 12 methylene groups). Microscopic investigations at the molecular resolution allow for detailed analysis of the effect of the alkyl spacer length on the type and the extent of the resulting 2D organization. It was demonstrated that bimesogens with shorter spacers (7 and 8 methylene units) organize in a similar manner characterized by the formation of two types of differently ordered monolayers: dense packed, wherein the molecules are oriented in one direction and ordered into parallel rows (layer structure), or less densely packed where they are organized into a chiral windmill-like structure. For derivatives with longer spacers (ranging from 9 to 12 methylene units) the additional effect of parity of carbon atoms in the spacer (even versus odd) is observed. In this range of the spacer lengths even membered bimesogens are also organized in a typical layer structure. However, odd-membered dimers exhibit a much more complex 2D supramolecular organization with a larger unit cell and a helical arrangement of the molecules. Careful comparison of this structure with the 3D structural data derived from the X-ray diffraction investigations of single crystals indicates that for these bimesogens a clear correlation exists between the observed complex 2D supramolecular organization in the monolayer and the organization in one of the crystallographic planes of the 3D nematic twist-bent phase.

We report the synthesis of the first stable, solution-processable and photocrosslinkable hybrid organic/inorganic titanium dioxide nanorods as 'hairy rods' coated with phosphonate ligands with photoreactive coumarin groups located in a terminal position. The relationships between the chemical structure of the diethyl-ω-[(7-oxycoumaryl)- n -alkyl]phosphonate ligands on the ligand exchange rate (LER) and the solubility of the resultant ligand-stabilized titanium dioxide nanorods in organic solvents are elucidated. These TiO 2 nanorods, with an organic ligand coating, are short enough (aspect ratio = 5-8) to be dissolved in chlorobenzene at high concentrations, but long enough to form lyotropic nematic liquid crystals. These colloidal solutions are used to deposit a thin, uniform layer of hybrid organic/inorganic TiO 2 nanorods with their long axes in the plane of a flat, smooth substrate through a self-organization process. Standard photolithographic patterning creates an insoluble dielectric layer of the desired thickness, smoothness and uniformity and with a dielectric constant of sufficient magnitude, k = 8, suitable for the fabrication of multilayer, plastic electronic devices using solution-based fabrication techniques, such as ink-jet printing, used in roll-to-roll manufacturing., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Selective reflection of light by oblique helicoidal cholesteric (Ch OH ) can be tuned in a very broad spectral range by an applied electric field. In this Letter, we demonstrate that the peak wavelength of the selective reflection can be controlled by the surface alignment of the director in sandwich cells. The peak wavelength is blue-shifted when the surface alignment is perpendicular to the bounding plates and red-shifted when it is planar. The effect is explained by the electric field redistribution within the cell caused by a spatially varying heliconical Ch OH structure. The observed phenomenon can be used in sensing applications.

Photopolymerization of a reactive mesogen mixed with a mesogenic dimer, shown to exhibit the twist-bend nematic phase (N TB ), reveals the complex structure of the self-deformation patterns observed in planar cells. The polymerized reactive mesogen retains the structure formed by liquid crystalline molecules in the twist bend phase, thus enabling its observation by scanning electron microscopy (SEM). Hierarchical ordering scales ranging from tens of nanometers to micrometers are imaged in detail. Submicron features, anticipated from earlier X-ray experiments, are visualized directly. In the self-deformation stripes formed in the N TB phase, the average director field is found tilted in the cell plane by an angle of up to 45° from the cell rubbing direction. This tilt explains the sign inversion being observed in the electro-optical studies.

Using a magnetically aligned liquid crystal mixture containing a novel Se-labelled dimer and the difluoroterphenyl dimer DTC5C7, the twist-bend nematic phase (N tb ) was studied by the resonant scattering of hard X-rays and by conventional small and wide-angle X-ray scattering (SAXS, WAXS). Resonant diffraction spots indicated a helix with a 9-12 nm pitch in the N tb phase and an unprecedentedly high helix orientation. This enabled deconvolution of global and local order parameters. These findings, combined with the simultaneously recorded resonant and non-resonant SAXS and WAXS data, allowed us to construct a locally layered molecular model of the N tb phase, where the average twisted conformation of each molecule was idealised as a helical segment, matching the local heliconical director field. The dimers were found to be less bent in the N tb phase than in their minimum energy conformation, and straightening further with increasing temperature. It is proposed that on further heating their low bend angle allows the transition to the normal nematic phase, where the molecules can freely move longitudinally, without the need to perform screw-like motion as in the N tb phase. At the low-temperature end, the increasing molecular twist becomes unsustainable, leading to a transition to a smectic phase, where no twist is required.

The nematic twist-bend (TB) phase, exhibited by certain achiral thermotropic liquid crystalline (LC) dimers, features a nanometer-scale, heliconical rotation of the average molecular long axis (director) with equally probable left- and right-handed domains. On meso to macroscopic scales, the TB phase may be considered as a stack of equivalent slabs or "pseudo-layers", each one helical pitch in thickness. The long wavelength fluctuation modes should then be analogous to those of a smectic-A phase, and in particular the hydrodynamic mode combining "layer" compression and bending ought to be characterized by an effective layer compression elastic constant B eff and average director splay constant K. The magnitude of K is expected to be similar to the splay constant of an ordinary nematic LC, but due to the absence of a true mass density wave, B eff could differ substantially from the typical value of ∼10 6 Pa in a conventional smectic-A. Here we report the results of a dynamic light scattering study, which confirms the "pseudo-layer" structure of the TB phase with B eff in the range 10 3 -10 4 Pa. We show additionally that the temperature dependence of B eff at the TB to nematic transition is accurately described by a coarse-grained free energy density, which is based on a Landau-deGennes expansion in terms of a heli-polar order parameter that characterizes the TB state and is linearly coupled to bend distortion of the director.

We present structural studies of a dimeric compound composed of a central heptyl spacer linking two mesogens consisting of terphenyl units at which two adjacent fluoro groups are attached to each central ring. The terminal rings are linked to pentyl chains as terminal groups. The material exhibits a nematic-nematic transition and a low temperature modulated phase. The higher temperature nematic phase was found to exhibit an anomaly of the bend elastic constant similar to that of the dimers with N-Ntb phase sequence, and the physical properties of the low-temperature nematic phase are similar to those of the known Ntb materials. The structure of the low-temperature modulated smectic/columnar phase is described together with its ability to form freely suspended films and fibres. The relation of the modulated structure to the fibre formation and to the appearance of the labyrinthine instability in freely-suspended films is discussed.

We have determined the nematic-isotropic transition temperature as a function of an applied magnetic field in three different thermotropic liquid crystalline dimers. These molecules are comprised of two rigid calamitic moieties joined end to end by flexible spacers with odd numbers of methylene groups. They show an unprecedented magnetic field enhancement of nematic order in that the transition temperature is increased by up to 15 K when subjected to a 22 T magnetic field. The increase is conjectured to be caused by a magnetic-field-induced decrease of the average bend angle in the aliphatic spacers connecting the rigid mesogenic units of the dimers.

We report a columnar superlattice formed by blends of dendron-like Li 3,4,5-tris(n-alkoxy)benzoates with n-alkanes. Without the alkane, the wedge-shaped molecules form liquid crystal columns with 3 dendrons in a supramolecular disk. The same structure exists in the blend, but on heating one dendron is expelled from the disks in every third column and is replaced by the alkane. This superlattice of unequal columns is confirmed by complementary X-ray and neutron diffraction studies. Lateral thermal expansion of dendrons normally leads to the expulsion of excess molecules from the column, reducing the column diameter. However, in the already narrow columns of pure Li salt, expulsion of one of only three dendrons in a disk is not viable. The added alkane facilitates the expulsion, as it replaces the missing dendron. Replacing the alkane with a functional compound can potentially lead to active nanoarrays with relatively large periodicity by using only small molecules.

The nematic twist-bend (NTB) phase, exhibited by certain thermotropic liquid crystalline (LC) dimers, represents a new orientationally ordered mesophase - the first distinct nematic variant discovered in many years. The NTB phase is distinguished by a heliconical winding of the average molecular long axis (director) with a remarkably short (nanoscale) pitch and, in systems of achiral dimers, with an equal probability to form right- and left-handed domains. The NTB structure thus provides another fascinating example of spontaneous chiral symmetry breaking in nature. The order parameter driving the formation of the heliconical state has been theoretically conjectured to be a polarization field, deriving from the bent conformation of the dimers, that rotates helically with the same nanoscale pitch as the director field. It therefore presents a significant challenge for experimental detection. Here we report a second harmonic light scattering (SHLS) study on two achiral, NTB-forming LCs, which is sensitive to the polarization field due to micron-scale distortion of the helical structure associated with naturally-occurring textural defects. These defects are parabolic focal conics of smectic-like "pseudo-layers", defined by planes of equivalent phase in a coarse-grained description of the NTB state. Our SHLS data are explained by a coarse-grained free energy density that combines a Landau-deGennes expansion of the polarization field, the elastic energy of a nematic, and a linear coupling between the two.

In this work the mechanisms leading to the enhancement of optical nonlinearity of nematic liquid crystalline material through localized heating by doping the liquid crystals (LCs) with gold nanoparticles (GNPs) are investigated. We present some experimental and theoretical results on the effect of voltage and nanoparticle concentration on the nonlinear response of GNP-LC suspensions. The optical nonlinearity of these systems is characterized by diffraction measurements and the second order nonlinear refractive index, n2, is used to compare systems with different configurations and operating conditions. A theoretical model based on heat diffusion that takes into account the intensity and finite size of the incident beam, the nanoparticle concentration dependent absorbance of GNP doped LC systems and the presence of bounding substrates is developed and validated. We use the model to discuss the possibilities of further enhancing the optical nonlinearity.

The order parameter, Szz, where z is the para axis of the difluoroterphenyl groups in DTC5C9, has been obtained from chemical shift anisotropies measured by (13)C - {(1)H} NMR experiments at temperatures throughout the nematic, NU, and twist-bend nematic, NTB, phases shown by this compound. The order parameter temperature profiles are unusual in having a maximum value in the NU phase and then decreasing until the NTB phase is reached. There is a small discontinuity (∼2%) in Szz at TNNTB and then a gradual decrease until a new phase appears. This behaviour is interpreted as revealing a temperature-dependent tilting of local directors in both phases away from the applied magnetic field direction. In the enantiomorphic twist-bend phase this tilt is consistent with the structure of the phase as a helical arrangement of local directors, whilst in the high-temperature non-chiral nematic the tilt must involve a non-chiral arrangement. It is proposed that in both phases the tilting of directors has a common origin in the bent shape of the molecules.

The phase behaviour of mixtures between two symmetric dimers, CBC9CB and the ether-linked analogue CBOC9OCB was investigated by Polarizing Optical Microscopy (POM), Differential Scanning Calorimetry (DSC) and X-Ray Diffraction (XRD) studies. The dimeric constituents are fully miscible and the construction of a temperature-composition phase diagram reveals a surprising amplification of the stability of the Nx phase in compositions of up to 37 wt% of CBOC9OCB in CBC9CB. The origin for this enhancement of stability is discussed and an explanation based on chiral recognition is developed.

Gold nanoparticles have been prepared and surface-functionalized with a 1:1 molar mixture of a hexylthiol ligand and a chiral mesogenic ligand consisting of a cholesterylbenzoate attached via an undecylthiol spacer. Grazing incidence X-ray diffraction showed that upon annealing a columnar liquid crystal (LC) structure develops with the nanoparticles forming strings on a regular oblique 2d lattice. Synchrotron radiation circular dichroism is substantially enhanced upon the isotropic-LC transition. In the proposed structural model, layers of Au columns rotate by a small angle relative to their neighbors, with the columns winding around a helical axis. The work demonstrates that it is possible to obtain chiral LC superstructures from nanoparticles coated with chiral mesogen without the addition of a separate LC or chiral dopants. The results provide direction in the development of plasmonic metamaterials interacting selectively with circularly polarized light.

NMR measurements on a selectively deuterated liquid crystal dimer CB-C9-CB, exhibiting two nematic phases, show that the molecules in the lower temperature nematic phase, N(X), experience a chiral environment and are ordered about a uniformly oriented director throughout the macroscopic sample. The results are contrasted with previous interpretations that suggested a twist-bend spatial variation of the director. A structural picture is proposed wherein the molecules are packed into highly correlated chiral assemblies.

We designed a new method for preparation of liquid marbles by using hydrophilic particles. Salt-hydrogel marbles were prepared by atomising droplets of hydrogel solution in a cold air column followed by rolling of the collected hydrogel microbeads in a bed of micrometre sized salt particles. Evaporation of the water from the resulting salt marbles with a hydrogel core yielded hollow-shell salt microcapsules. The method is not limited to hydrophilic particles and could potentially be also applied to particles of other materials, such as graphite, carbon black, silica and others. The structure and morphology of the salt-hydrogel marbles were analysed by SEM and their particle size distributions were measured. We also tested the dissolution times of the dried salt marbles and compared them with those of table salt samples under the same conditions. The high accessible surface area of the shell of salt microcrystals allows a faster initial release of salt from the hollow-shell salt capsules upon their dissolution in water than from the same amount of table salt. The results suggest that such hollow-shell particles could find applications as a table salt substitute in dry food products and salt seasoning formulations with reduced salt content without the loss of saltiness.

Liquid crystals (LCs) represent a challenging group of materials for direct transmission electron microscopy (TEM) studies due to the complications in specimen preparation and the severe radiation damage. In this paper, we summarize a series of specimen preparation methods, including thin film and cryo-sectioning approaches, as a comprehensive toolset enabling high-resolution direct cryo-TEM observation of a broad range of LCs. We also present comparative analysis using cryo-TEM and replica freeze-fracture TEM on both thermotropic and lyotropic LCs. In addition to the revisits of previous practices, some new concepts are introduced, e.g., suspended thermotropic LC thin films, combined high-pressure freezing and cryo-sectioning of lyotropic LCs, and the complementary applications of direct TEM and indirect replica TEM techniques. The significance of subnanometer resolution cryo-TEM observation is demonstrated in a few important issues in LC studies, including providing direct evidences for the existence of nanoscale smectic domains in nematic bent-core thermotropic LCs, comprehensive understanding of the twist-bend nematic phase, and probing the packing of columnar aggregates in lyotropic chromonic LCs. Direct TEM observation opens ways to a variety of TEM techniques, suggesting that TEM (replica, cryo, and in situ techniques), in general, may be a promising part of the solution to the lack of effective structural probe at the molecular scale in LC studies., (© 2014 Wiley Periodicals, Inc.)

The construction of liquid crystal compositions consisting of the dimeric liquid crystal, CB&#95;C9&#95;CB (cyanobiphenyl dimer = 1'',9''-bis(4-cyanobiphenyl-4'-yl)nonane), and the range of nematic systems is explored. The materials include a laterally functionalized monomer, which was used to construct a phase diagram with CB&#95;C9&#95;CB , as well as one laterally linked dimer liquid crystal material and two liquid crystal gold nanoparticle (LC-Au-NPs) systems. For the Au-NP-LCs, the NP diameters were varied between ~3.3 nm and 10 nm. Stable mixtures that exhibit a nematic-nematic phase transition are reported and were investigated by POM (polarizing optical microscopy), DSC (differential scanning calorimetry) and X-ray diffraction studies.

We perform optical, surface anchoring, and textural studies of an organo-siloxane "tetrapode" material in the broad temperature range of the nematic phase. The optical, structural, and topological features are compatible with the uniaxial nematic order rather than with the biaxial nematic order, in the entire nematic temperature range -25 °C < T < 46 °C studied. For homeotropic alignment, the material experiences surface anchoring transition, but the director can be realigned into an optically uniaxial texture by applying a sufficiently strong electric field. The topological features of textures in cylindrical capillaries, in spherical droplets and around colloidal inclusions are consistent with the uniaxial character of the long-range nematic order. In particular, we observe isolated surface point defects - boojums and bulk point defects - hedgehogs that can exist only in the uniaxial nematic liquid crystal.

A composite material that leads to self organization of mesogen-coated gold nanospheres is synthesized and shows enhanced anisotropic optical properties due to synergistic effects of the mesogens intrinsic birefringence and its ability to drive the self-assembly process into highly anisotropic architectures with densely packed nanospheres. Such nanoengineered matter sustains a response beyond that achievable by its individual constituents, i.e., a metamaterial., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Biaxial (N(B)) and uniaxial nematic (N(U)) phase behavior was detected and confirmed for an organosiloxane tetrapode material using capacitance and birefringence measurements. Elastic constants, permittivities at two distinct low frequencies, and birefringencies were determined as a function of temperature over both the N(U) and the N(B) phase ranges. The N(U)-N(B) transition is clearly observed in the birefringencies and conoscopy data. A temperature dependent cross-over frequency is also detected in this material for the permittivities, allowing the electrical switching of both planar and homeotropic aligned samples.

A state of matter in which molecules show a long-range orientational order and no positional order is called a nematic liquid crystal. The best known and most widely used (for example, in modern displays) is the uniaxial nematic, with the rod-like molecules aligned along a single axis, called the director. When the molecules are chiral, the director twists in space, drawing a right-angle helicoid and remaining perpendicular to the helix axis; the structure is called a chiral nematic. Here using transmission electron and optical microscopy, we experimentally demonstrate a new nematic order, formed by achiral molecules, in which the director follows an oblique helicoid, maintaining a constant oblique angle with the helix axis and experiencing twist and bend. The oblique helicoids have a nanoscale pitch. The new twist-bend nematic represents a structural link between the uniaxial nematic (no tilt) and a chiral nematic (helicoids with right-angle tilt).

The synthesis of a novel class of organosiloxane oligopodes, based on an axially chiral binaphthalene core is described and their mesogenic properties are fully characterised.