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Ionic liquid crystals (ILCs) combine the ion mobility of ionic liquids with the order and self-assembly of thermotropic mesophases. To understand the role of the anion in ILCs, wedge-shaped arylguanidinium salts with tetradecyloxy side chains were chosen as benchmark systems and their liquid crystalline self-assembly in the bulk phase as well as their electrochemical behavior in solution were studied depending on the anion. Differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS, SAXS) experiments revealed that for spherical anions, the phase width of the hexagonal columnar mesophase increased with the anion size, while for non-spherical anions, the trends were less clear cut. Depending on the anion, the ILCs showed different stability towards electrochemical oxidation and reduction with the most stable being the PF6 based compound. Cyclic voltammetry (CV) and density functional theory (DFT) calculations suggest a possible contribution of the guanidinium cation to the oxidation processes. [ABSTRACT FROM AUTHOR]

The combination of lyotropic liquid crystals (LLCs) and low-molecular-weight gelators (LMWGs) for the formation of lyotropic liquid crystal gels (LLC gels) leads to a versatile and complex material combining properties of both parent systems. We gelled the calamitic nematic NC phases of a binary and ternary system using the LMWG 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). This binary system consists of the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water, whereas the ternary system consists of the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C14TAB), the cosurfactant n-decanol, and water. Though containing similar surfactants, the gelled NC phases of the binary and ternary systems show differences in their visual and gel properties. The gelled NC phase of the binary system remains clear for several days after preparation, whereas the gelled NC phase of the ternary system turns turbid within 24 h. We investigated the time evolution of the gel strength with oscillation rheology measurements (a) within the first 24 h and (b) up to two weeks after gel formation. The shape of the fibers was investigated over different time scales with freeze fracture electron microscopy (FFEM). We demonstrate that despite their similarities, the two LLC gels also have distinct differences. [ABSTRACT FROM AUTHOR]

We present a new ferroelectric nematic material, 4-((4′-((trans)-5-ethyloxan-2-yl)-2′,3,5,6′-tetrafluoro-[1,1′-biphenyl]-4-yl)difluoromethoxy)-2,6-difluorobenzonitrile (AUUQU-2-N) and its higher homologues, the molecular structures of which include fluorinated building blocks, an oxane ring, and a terminal cyano group, all contributing to a large molecular dipole moment of about 12.5 D. We observed that AUUQU-2-N has three distinct liquid crystal phases, two of which were found to be polar phases with a spontaneous electric polarization Ps of up to 6 µC cm–2. The highest temperature phase is a common enantiotropic nematic (N) exhibiting only field-induced polarization. The lowest-temperature, monotropic phase proved to be a new example of the ferroelectric nematic phase (NF), evidenced by a single-peak polarization reversal current response, a giant imaginary dielectric permittivity on the order of 103, and the absence of any smectic layer X-ray diffraction peaks. The ordinary nematic phase N and the ferroelectric nematic phase NF are separated by an antiferroelectric liquid crystal phase which has low permittivity and a polarization reversal current exhibiting a characteristic double-peak response. In the polarizing light microscope, this antiferroelectric phase shows characteristic zig-zag defects, evidence of a layered structure. These observations suggest that this is another example of the recently discovered smectic ZA (SmZA) phase, having smectic layers with the molecular director parallel to the layer planes. The diffraction peaks from the smectic layering have not been observed to date but detailed 2D X-ray studies indicate the presence of additional short-range structures including smectic C-type correlations in all three phases—N, SmZA and NF—which may shed new light on the understanding of polar and antipolar order in these phases. [ABSTRACT FROM AUTHOR]

We present a new ferroelectric nematic material, 4-((4′-((trans)-5-ethyloxan-2-yl)-2′,3,5,6′-tetrafluoro-[1,1′-biphenyl]-4-yl)difluoromethoxy)-2,6-difluorobenzonitrile (AUUQU-2-N) and its higher homologues, the molecular structures of which include fluorinated building blocks, an oxane ring, and a terminal cyano group, all contributing to a large molecular dipole moment of about 12.5 D. We observed that AUUQU-2-N has three distinct liquid crystal phases, two of which were found to be polar phases with a spontaneous electric polarization Ps of up to 6 µC cm–2. The highest temperature phase is a common enantiotropic nematic (N) exhibiting only field-induced polarization. The lowest-temperature, monotropic phase proved to be a new example of the ferroelectric nematic phase (NF), evidenced by a single-peak polarization reversal current response, a giant imaginary dielectric permittivity on the order of 103, and the absence of any smectic layer X-ray diffraction peaks. The ordinary nematic phase N and the ferroelectric nematic phase NF are separated by an antiferroelectric liquid crystal phase which has low permittivity and a polarization reversal current exhibiting a characteristic double-peak response. In the polarizing light microscope, this antiferroelectric phase shows characteristic zig-zag defects, evidence of a layered structure. These observations suggest that this is another example of the recently discovered smectic ZA (SmZA) phase, having smectic layers with the molecular director parallel to the layer planes. The diffraction peaks from the smectic layering have not been observed to date but detailed 2D X-ray studies indicate the presence of additional short-range structures including smectic C-type correlations in all three phases—N, SmZA and NF—which may shed new light on the understanding of polar and antipolar order in these phases. [ABSTRACT FROM AUTHOR]

Lyotropic liquid crystal gels (LLC gels) are versatile materials which combine the anisotropy of a liquid crystal with the mechanical stability of a gel. We succeeded in gelling the rare calamitic nematic NC phase of two different micellar LLC systems with the low molecular weight gelator (LMWG) 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). The systems of choice are: (1) a binary LLC system with the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water; (2) a ternary LLC system with the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C14TAB), n-decanol, and water. The obtained gels show optical birefringence and no macroscopic flow. Freeze fracture electron microscopy (FFEM) images show ribbon-like gel fibres that form the gel network and can stack into thicker bundles, while small-angle X-ray scattering (SAXS) confirms the coexistence of the nematic NC phase and the gel network. The growth of the gel network was monitored with time-resolved SAXS measurements. Additionally, significant gel ageing effects were observed in rheology measurements, showing that the gel strengthens with time. With this study, we considerably broaden the pool of available surfactant-based LLC gels and pave a way to macroscopically aligned LLC gels with the goal to apply them as stimuli-responsive actuators and sensors. [ABSTRACT FROM AUTHOR]

The use of thermally activated delayed fluorescence (TADF) emitters and emitters that show preferential horizontal orientation of their transition dipole moment (TDM) are two emerging strategies to enhance the efficiency of OLEDs. We present the first example of a liquid crystalline multi‐resonance TADF (MR‐TADF) emitter, DiKTa‐LC. The compound possesses a nematic liquid crystalline phase between 80 °C and 110 °C. Importantly, the TDM of the spin‐coated film shows preferential horizontal orientation, with an anisotropy factor, a, of 0.28, which is preserved in doped poly(vinylcarbazole) films. Green‐emitting (λEL=492 nm) solution‐processed OLEDs based on DiKTa‐LC showed an EQEmax of 13.6 %. We thus demonstrate for the first time how self‐assembly of a liquid crystalline TADF emitter can lead to the so‐far elusive control of the orientation of the transition dipole in solution‐processed films, which will be of relevance for high‐performance solution‐processed OLEDs. [ABSTRACT FROM AUTHOR]

The use of thermally activated delayed fluorescence (TADF) emitters and emitters that show preferential horizontal orientation of their transition dipole moment (TDM) are two emerging strategies to enhance the efficiency of OLEDs. We present the first example of a liquid crystalline multi‐resonance TADF (MR‐TADF) emitter, DiKTa‐LC. The compound possesses a nematic liquid crystalline phase between 80 °C and 110 °C. Importantly, the TDM of the spin‐coated film shows preferential horizontal orientation, with an anisotropy factor, a, of 0.28, which is preserved in doped poly(vinylcarbazole) films. Green‐emitting (λEL=492 nm) solution‐processed OLEDs based on DiKTa‐LC showed an EQEmax of 13.6 %. We thus demonstrate for the first time how self‐assembly of a liquid crystalline TADF emitter can lead to the so‐far elusive control of the orientation of the transition dipole in solution‐processed films, which will be of relevance for high‐performance solution‐processed OLEDs. [ABSTRACT FROM AUTHOR]

We report the observation of the smectic AF, a liquid crystal phase of the ferroelectric nematic realm. The smectic AF is a phase of small polar, rod-shaped molecules that form two-dimensional fluid layers spaced by approximately the mean molecular length. The phase is uniaxial, with the molecular director, the local average long-axis orientation, normal to the layer planes, and ferroelectric, with a spontaneous electric polarization parallel to the director. Polarization measurements indicate almost complete polar ordering of the ~10 Debye longitudinal molecular dipoles, and hysteretic polarization reversal with a coercive field ~2 × 105 V/m is observed. The SmAF phase appears upon cooling in two binary mixtures of partially fluorinated mesogens: 2N/DIO, exhibiting a nematic (N)–smectic ZA (SmZA)–ferroelectric nematic (NF)–SmAF phase sequence, and 7N/DIO, exhibiting an N–SmZA–SmAF phase sequence. The latter presents an opportunity to study a transition between two smectic phases having orthogonal systems of layers. [ABSTRACT FROM AUTHOR]

Simple smectic A liquid crystal phases with different types of prescribed orientational distribution functions have been simulated and compared in order to study the possibility to distinguish between the Maier-Saupe type and cone-like orientational distributions using the popular method of Davidson et al. [J. Phys. II 5, 113 (1995)]. This method has been used to extract the orientational distribution functions from simulated diffraction patterns, and the results have been compared with actual distribution functions which have been prescribed during simulations. It has been shown that it is indeed possible to distinguish between these two qualitatively different types of orientational distribution already from the shape of the 2D diffraction pattern. Moreover, typical experimental diffraction patterns for "de Vries"-type smectic liquid crystals appear to be close to the ones which have been simulated using the prescribed Maier-Saupe orientational distribution function. [ABSTRACT FROM AUTHOR]

Ionic liquid crystals (ILCs), that is, ionic liquids exhibiting mesomorphism, liquid crystalline phases, and anisotropic properties, have received intense attention in the past years. Among others, this is due to their special properties arising from the combination of properties stemming from ionic liquids and from liquid crystalline arrangements. Besides interesting fundamental aspects, ILCs have been claimed to have tremendous application potential that again arises from the combination of properties and architectures that are not accessible otherwise, or at least not accessible easily by other strategies. The current review highlights recent developments in ILC research, starting with some key fundamental aspects. Further subjects covered include the synthesis and variations of modern ILCs, including the specific tuning of their mesomorphic behavior. The review concludes with reflections on some applications that may be within reach for ILCs and finally highlights a few key challenges that must be overcome prior and during true commercialization of ILCs. [ABSTRACT FROM AUTHOR]

Self‐assembly is one of the crucial mechanisms allowing the design multifunctional materials. Soft hybrid materials contain components of different natures and exhibit competitive interactions which drive self‐organization into structures of a particular function. Here a novel type of a magnetic hybrid material where the molecular tilt can be manipulated through a delicate balance between the topologically‐assisted colloidal self‐assembly of magnetic nanoparticles and the anisotropic molecular interactions in a liquid crystal matrix is demonstrated. [ABSTRACT FROM AUTHOR]

Smectic liquid crystals with a low layer contraction of less than 1% upon an SmA to SmC transition are referred to as 'de Vries-like'. These materials have attracted considerable attention as possible alternative to problems with surface-stabilized ferroelectric liquid crystals in liquid crystal displays. The 'de Vries-like' properties of liquid crystals with nanosegregating carbosilane segments are enhanced by lengthening the carbosilane end-groups from mono- to tricarbosilane. The observed enhancement is thought to arise from an increase in the cross-section of the free volume in the hydrocarbon sub-layer. The hypothesis is tested by assuming that dimers with a tricarbosilane linking group have smaller time-averaged cross-sections. This paper reports the synthesis and characterization of two homologous series of liquid crystals and an investigation of their mesogenic properties as model systems employing liquid crystalline monomers (QL39-n) and dimers (QL40-n) comprising 2-phenylpyrimidine cores and tricarbosilane end-groups and spacers, respectively. We find that the QL39-n monomers form only a tilted SmC phase, whereas the QL40-n dimer forms an orthogonal SmA phase due to the tricarbosilane spacer will not have a spherically shape on the time average like that predicted for the tricarbosilane end-group. Results are discussed in the context of the timeaveraged cross-sections of the materials. [ABSTRACT FROM AUTHOR]

Selectively functionalized mesoporous silica may considerably advance heterogeneous catalysis through the controlled immobilization of highly selective complex catalysts inside the mesopores. However, spatially controlled functionalization and the precise analytical verification are still a challenge. In this publication, we report a method, which ensures a selective functionalization of the mesopore surface with a clickable linker and thus makes it possible to study confinement effects during catalyzed reactions. First, we passivate the silanol groups on the particle surface and in the pore entrances of the mesoporous silica material SBA‐15 with 1,1,1‐trimethyl‐N‐(trimethylsilyl)silanamine. Then we remove the template by solvent extraction and functionalize the pore walls with 3‐azidopropyltriethoxysilane before we click the catalyst. In initial experiments of asymmetric Rh‐catalyzed 1,2‐addition, we investigate the performance of a catalyst clicked selectively in the mesopores and compare it to the dissolved catalyst as well as to the catalyst immobilized exclusively on the external surface of SBA‐15. [ABSTRACT FROM AUTHOR]

Recent measurements of the elastic constants in lyotropic chromonic liquid crystals (LCLCs) have revealed an anomalously small twist elastic constant compared to the splay and bend constants. Interestingly, measurements of the elastic constants in the micellar lyotropic liquid crystals (LLCs) that are formed by surfactants, by far the most ubiquitous and studied class of LLCs, are extremely rare and report only the ratios of elastic constants and do not include the twist elastic constant. By means of light scattering, this study presents absolute values of the elastic constants and their corresponding viscosities for the nematic phase of a standard LLC composed of disk-shaped micelles. Very different elastic moduli are found. While the splay elastic constant is in the typical range of 1.5 pN as is true in general for thermotropic nematics, the twist elastic constant is found to be one order of magnitude smaller (0.30 pN) and almost two orders of magnitude smaller than the bend elastic constant (21 pN). These results demonstrate that a small twist elastic constant is not restricted to the special case of LCLCs, but is true for LLCs in general. The reason for this extremely small twist elastic constant very likely originates with the flexibility of the assemblies that are the building blocks of both micellar and chromonic lyotropic liquid crystals. [ABSTRACT FROM AUTHOR]

Surfactant-based lyotropic liquid crystal gels (LLCGs) are soft materials which combine the anisotropic order of a surfactant-based lyotropic liquid crystal with the mechanical stability of a gel. The most prominent example of a ''natural'' LLCG is the biological cell. This review summarizes potential applications of surfactant-based LLCGs and the different strategies via which these materials can be obtained. The main focus, however, is on gelation with low molecular weight gelators (LMWG), which form self-assembled fibrillar networks (SAFiN). We will discuss whether or not the resulting surfactantbased LLCGs are orthogonal self-assembled systems, i.e. systems where the two coexisting structures (lyotropic liquid crystal and SAFiN) form independently. [ABSTRACT FROM AUTHOR]

Thermotropic ionic liquid crystals based on the flavylium scaffold have been synthesized and studied for their structure‐properties relationship for the first time. The mesogens were probed by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X‐ray diffraction (XRD). Low numbers of alkoxy side chains resulted in smectic (SmA) and lamello‐columnar (LamCol) phases, whereas higher substituted flavylium salts showed Colro as well as ordered and disordered columnar (Colho, Colhd) mesophases. Mesophase width ranged from 13 K to 220 K, giving access to room temperature liquid crystals. The optical properties of the synthesized compounds were probed towards absorption and emission properties. Strong absorption with maxima between 444 and 507 nm was observed, and some chromophores were highly emissive with quantum yields up to 99 %. Ultimately, mesogenic and dye properties were examined by temperature‐dependent emissive experiments in the solid state. [ABSTRACT FROM AUTHOR]

We report results from laser light diffraction studies on the electric-field-induced dynamic modulation of the helical director configuration of SmC* liquid crystals. In contrast to what is predicted by common theoretical models for bulk samples, we found no increase of the helix pitch with increasing electric fields in planar-aligning cells. This can be explained by the appearance of disclinations that are pinned at the cell surfaces but also the large dimension of the sample cell along the helix axis is expected to play a role. Even more surprisingly, we found a decreasing pitch with an increasing field for one of the compounds investigated and a field-controllable rotation of the diffraction pattern around the sample cell normal in two other materials. [ABSTRACT FROM AUTHOR]

The smectic layer spacing of two homologous series of ferroelectric liquid crystal compounds was characterized by small-angle x-ray diffraction and different degrees of smectic layer shrinkage on cooling from the SmA* into the SmC* phase were observed. The smectic A*-smectic C* phase transition was further studied by measuring the thermal and electric field effects on the optical tilt angle and the electric polarization. With decreasing length of the alkyl terminal chain the phase transition changes from tricritical exhibiting high layer shrinkage to a pure second-order transition with almost no layer shrinkage. This is explained by the increased one-dimensional translational order of the smectic layers, which seems to promote the “de Vries”-type [Mol. Cryst. Liq. Cryst. 41, 27 (1977)] smectic A*-C* phase transition with no or little layer shrinkage. [ABSTRACT FROM AUTHOR]

The thermotropic smectic phases of amphiphilic 2-(trans-4-n-alkylcyclohexyl)-propane-1,3-diols were investigated by means of small- and wide-angle x-ray scattering and values of the smectic (bi-)layer spacing, the orientational order parameters 〈P2〉 and 〈P4〉, the orientational distribution function as well as the intralayer correlation length were extracted from the scattering profiles. The results for the octyl homolog indicate that these smectic phases combine a very high degree of smectic one-dimensional-translational order with remarkably low orientational order, the order parameter of which (〈P2〉≈0.56) is far below those values typically found in nonamphiphilic smectics. This combination, quite exceptional in thermotropic smectics, most likely originates from the intermolecular hydrogen bonding between the terminal diol groups which seems to be the specific driving force in the formation of the thermotropic smectic structure in these amphiphiles and leads to a type of microphase segregation. Even in the absence of a solvent, the liquid-crystalline ordering of the amphiphilic mesogens comes close to the structure of the so-called neat soaps, found in lyotropic liquid crystals. [ABSTRACT FROM AUTHOR]

By mixing the achiral liquid crystal HOAB, exhibiting a nematic (N)–smectic-C (SmC) mesophase sequence, with the chiral antiferroelectric liquid crystal (AFLC) (S,S)-M7BBM7, forming the antiferroelectric SmCa* phase, at least seven different mesophases have been induced which neither component forms on its own: a twist-grain-boundary (TGB*) phase, two or three blue phases, the untilted SmA* phase, as well as all three chiral smectic-C-type “subphases,” SmCα*, SmCβ*, and SmCγ*. The nature of the induced phases and the transitions between them were determined by means of optical and electro-optical investigations, dielectric spectroscopy, and differential scanning calorimetry. The induced phases can to a large extent be understood as a result of frustration, TGB* at the border between nematic and smectic, the subphases between syn and anticlinic tilted smectic organization. X ray scattering experiments reveal that the smectic layer spacing as well as the degree of smectic order is relatively constant in the whole mixture composition range in which AFLC behavior prevails, whereas both these parameters rapidly decrease as the amount of HOAB is increased to such an extent that no other smectic-C-type phase than SmC/SmC* exists. By tailoring the composition we are able to produce liquid crystal mixtures exhibiting unusual phase sequences, e.g., with a direct isotropic-SmCa* transition or a temperature range of the SmCβ* subphase of about 50 K. [ABSTRACT FROM AUTHOR]

An orientational order parameter is proposed for the isotropic to smectic CA* phase transition in antiferroelectric liquid crystals. A phenomenological theory is developed to describe the direct isotropic to smectic-CA* phase transition on the basis of a free energy expansion. The free energy is written in terms of the coupled order parameters including the antipolar correlations. We present a detailed analysis of the different phases that can occur and analyze the question: under which conditions a direct isotropic to smectic-CA* phase transition is possible when compared to other phase transitions? The theoretical results are compared with experimental results. © 2004 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A general thermodynamic description of the photoferroelectric effect, where the spontaneous polarization of a ferroelectric material is changed by interaction with light, is proposed. This description leads to a distinction between primary and secondary photoferroelectricity. At a certain reduced temperature, the primary photoferroelectric effect originates from the light-induced change in the polar ferroelectric order, whereas the secondary photoferroelectric effect is a purely thermodynamic consequence of the light-induced change in the ferroelectric transition temperature T[sub c]. Using simple approximations, the general theory was applied to photoferroelectric Sm-C[sup *] liquid crystals where the photoresponse is induced by the Z,E photoisomerization of azobenzene dopant molecules. The results agree with experimental data obtained for a photoferroelectric Sm-C[sup *] mixture containing 5 mol % of the photoisomerizable dopant 4,4'-bis-[(2-methyl)butyloxy]azobenzene dissolved in the commercial ferroelectric Sm-C[sup *] host phase abbreviated FLC 6430. [ABSTRACT FROM AUTHOR]

We investigate the origins of 'de Vries-like' liquid crystalline behaviour by introducing an ethynyl spacer in the core of the tricarbosilane-terminated 5-phenylpyrimidine mesogens QL16-6 and QL17-6. The rationale for this structural change is based on the assumption that an ethynyl spacer would create more free volume in the core sub-layer and therefore decrease the orientational order parameter S2 in the SmA phase. The tricarbosilane-terminated mesogens WL41-5 and WL42-6 with a 5-(phenylethynyl)pyrimidine core in either a normal or inverted orientation were synthesised, and their mesomorphic and 'de Vries-like' properties characterised using polarised optical microscopy, differential scanning calorimetry, birefringence measurements, small–angle (SAXS) and 2D X-ray scattering. Reduction factors R derived from SAXS and optical tilt angle measurements suggest that neither WL41-5 (R = 0.49) nor WL42-6 (R = 0.80) exhibit 'de Vries-like' properties. The S2(T) profiles show an increase in orientational order with decreasing temperature and a sharp discontinuity at the SmA-SmC transition, which is consistent with 'de Vries-like' behaviour. However, the Leff(T) profiles suggest an increase in interdigitation that reduces the positive effect of increasing S2 in compensating for the molecular tilt. [ABSTRACT FROM AUTHOR]

In 2001 Hanna et al. reported time of flight (ToF) experiments on the liquid-crystalline 5,5′′-dioctyl-2,2′:5′,2′′-terthiophene (8-TTP-8) and observed high charge carrier mobilities which made liquid-crystalline terthiophenes a promising class of materials for organic semiconductors. We now report detailed investigations on the structures of the smectic 8-TTP-8 phases – smectic C, smectic F and crystal G – and their impact on 2D charge carrier mobility in field-effect transistors (FETs). We found shear alignment to be a very simple and effective method to align the smectic phases as an active layer in FETs. Depending on the fluidity of the smectic phase the effective FET mobilities are far less reduced in comparison to the ToF mobilities than in the case of 1D columnar materials. The shear alignment in orthogonal directions further allowed the measurement of the anisotropy of mobility along and normal to the director tilt direction of the smectic phases. The anisotropy was found to be surprisingly high (namely μ‖/μ⊥ = 5 in crystal G) even though the director tilt angle is about 15 degrees rather low. The large anisotropy of the charge carrier mobility indicates that the quadrupolar ordering in the tilted smectic phases is connected to a face-on orientation of the aromatic terthiophene cores, which effectively enhances the charge transport in the tilt direction. [ABSTRACT FROM AUTHOR]

In de Vries smectic liquid crystals, the transition from the orthogonal smectic A (SmA) to the tilted smectic C (SmC) phase occurs with essentially no decrease in smectic layer thickness. This unusual behaviour is commonly explained assuming a 'hollow-cone' or 'volcano-like' orientational distribution function (ODF) of rod-like molecules in SmA and the transition to SmC being a pure disorder-order transition in the molecular tilt directions. However, even after 20 years of extensive investigations, the experimental confirmation of this ad hoc model is still inconclusive. While optical and electro-optic studies of many de Vries smectics can be readily explained with the hollow-cone model, X-ray diffraction (XRD) studies as well as many polarised Raman spectroscopy (PRS) studies support a broad Maier-Saupe distribution of a sugarloaf-like shape. We review and summarise X-ray, electro-optic and PRS results on the ODFs in the SmA phases of materials claimed to be of the de Vries type and discuss how seemingly contradicting findings can be true at the same time. In molecules where the core is far from collinear with the long molecular axis, the cores may exhibit a volcano ODF while the molecular axes exhibit a sugarloaf ODF. [ABSTRACT FROM AUTHOR]

Large (many mm long) closed tubes from liquid crystalline (LC)-elastomers can be prepared in a microfluidic setup by photopolymerization of an LC-monomer mixture. In these tubes, the director of the LC-phase is oriented parallel to their long axes as proven by X-ray measurements, thus leading to shortening at the transition to the isotropic phase while their walls become thicker simultaneously. The process of tube preparation relies on an appropriate choice of 3 immiscible phases in the microfluidic setup (continuous, LC-monomer and inner phase) as well as their interfacial tensions. Water can be used as the inner phase in combination with a selective detergent (an amphiphilic block copolymer from PNIPAM and the LC-polymer) to reduce the LC/water surface tension. In this way, long actuating (up to 50%) tubes can be prepared either from a thermotropic LC-elastomer or from an azo-containing LC-elastomer with the latter being both thermo- and photo-responsive. By irradiation of individual tubes consisting of the azo-system with white (trans–cis) or red light (cis–trans), actuations of up to 29% can be achieved. The contraction (shortening) of the tubes thereby requires about 10 seconds, while the photochemical reisomerization needs about 230 seconds. This sets the time frame for the tubes’ photochemical actuation. [ABSTRACT FROM AUTHOR]

A series of cyanobiphenyl dimers attached via alkoxy spacers to a central malonate were prepared, and the mesomorphic behaviour was studied by differential scanning calorimetry (DSC), polarised optical microscopy and X-ray diffraction (Wide-angle X-ray scattering and Small-angle X-ray scattering). Depending on spacer lengths and substitution of the malonate, nematic and smectic A mesophases with pronounced odd-even effect were observed. C-2-unsubstituted malonates formed nematic phases for chain lengths C6-C14, while C12 and C14 homologues displayed additional smectic A phases. In contrast, malonates with fluorinated tails at C-2 displayed exclusively smectic A phases. Remarkably, the X-ray diffraction profile of the smectic A phase of the C-2-unsubstituted C12 malonate showed a fundamental (001) and the corresponding third-order (003) diffraction peak, but no (002) reflection. Using Fourier analysis, the diffraction pattern was converted to an electron density profile, which was in good agreement with the proposed packing model of the SmA mesophase based on a horseshow- or hairpin-like conformation of the malonate. [ABSTRACT FROM AUTHOR]

Under mild conditions, PPO–PEO–PPO (“reverse Pluronics”) and PBO–PEO–PBO copolyether were generated by way of N-heterocyclic olefin-based organocatalysis. Reverse Pluronics with molar masses ＞ 20 000 g mol−1 could be synthesized with excellent control (ĐM≤ 1.03) and were converted into (ordered) mesoporous carbons via organic self-assembly to showcase the need for tailor-made copolymer as structure-directing agent. [ABSTRACT FROM AUTHOR]

Abstract: The tilted smectic C phase is a rather uncommon phase in ionic liquid crystals (ILCs), whereas the orthogonal smectic A phase is the most common phase in ILCs. We now present 2 new groups of mesogens with an azobenzene core that exhibit smectic C as well as smectic A phases. Their phase sequences and tilt angles were studied by polarizing microscopy, and their temperature‐dependent layer spacings and orientational order parameters were investigated by X‐ray diffraction. We present 1 new amidinium azobenzene mesogen that forms enantiotropic smectic C and A phases and another amidinium as well as 2 new guanidinium azobenzene mesogens that exhibit monotropic smectic C and enantiotropic smectic A phases. With this study, we show that azobenzene is indeed an SmC‐promoting group in ILCs. Comparing these results with our earlier results on azobenzenes with an N‐methylimidazolium head group (N Kapernaum et al, ChemPhysChem 2016, 17, 4116‐4123), we show that the aromaticity of the imidazolium head group plays an important role in the formation of smectic C phases. [ABSTRACT FROM AUTHOR]

We report the results of a study in which we introduce a tricarbosilane end-group in a mesogenic scaffold derived from an axially chiral biphenyl with a large transverse dipole moment. This structural modification is intended to promote the formation of a chiral smectic C (SmC*) phase, with the aim of discovering a mesogen with a virtual transition temperature to a proper ferroelectric phase (To) that approaches the crystal-SmC* melting point. We show herein that the combination of a 4-pentylbicyclo[2.2.2]octane-1-carboxylate chain and a tricarbosilane-terminated 4-alkoxybenzoate chain gives a mesogen (R,S)-WL43 forming an enantiotropic orthogonal smectic A (SmA) phase and a higher order tilted smectic phase. Substitution of the 4-pentylbicyclo[2.2.2]octane-1-carboxylate group with a trans-4-pentylcyclohexane-1-carboxylate group gives a mesogen (R,S)-WL45 forming monotropic SmA and SmC phases. The SmC* phase formed by the enantiomerically pure (R)-WL45 exhibits Goldstone-mode switching characteristic of a surface-stabilized FLC, but its spontaneous polarization PS is too low to be measured by conventional methods. [ABSTRACT FROM AUTHOR]

The recent discovery of a new lyotropic liquid crystal phase, the structure and properties of which are analogous to the chiral ferroelectric smectic C-phase (SmC*) in thermotropics, was based on a tailored amphiphile structure in which a tilt-promoting mesogenic core was linked to a chiral diol-headgroup via a hydrophilic ethylene glycol spacer [J. R. Bruckner et al., Angew. Chem., Int. Ed., 2013, 52, 8934–8937]. However, so far there is only one example of this general amphiphile structure known to form the new lyotropic SmC* phase in mixtures with water and with formamide. In an attempt to systematically elucidate the underlying structure–property relations we now report two new amphiphiles leading to lyotropic SmC* phases. These amphiphiles are derived from the parent amphiphile structure by (i) an elongation of the hydrophilic ethylene glycol spacer and (ii) an exchange of the original 2-phenylpyrimidine core by an even more tilt-promoting fluorenone core. Our investigations also reveal that the formation of the lyotropic SmC* phase is highly sensitive to exchanging or enlarging a building block of the primary material. [ABSTRACT FROM AUTHOR]

Synthetic strategies were developed to prepare l-tyrosine-based ionic liquid crystals with structural variations at the carboxylic and phenolic OH groups as well as the amino functionality. Salt metathesis additionally led to counterion variation. The liquid-crystalline properties were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and X-ray diffraction (WAXS, SAXS). The symmetrical ILC chlorides bearing the same alkyl chain at both the ester and ether but either an acyclic or cyclic guanidinium group displayed enantiotropic SmA2 mesophases with phase widths of 31-88 K irrespective of the head group. It was particularly the replacement of chloride in the acyclic guanidinium ILC by hexafluorophosphate that induced a phase change from SmA2 to Colr. This phase change was attributed to a higher curvature of the interface due to the larger anion, which increased the effective head group cross-sectional area of the amphiphilic ILC. The unsymmetrical acyclic guanidinium chlorides, bearing a constant C14 ester and variable alkyl chains on the phenolic position, formed enantiotropic SmA2 phases. The derivative with the largest difference in chain lengths, however, displayed a Colr phase, resulting from discoid aggregates of the cone-shaped guanidinium chloride. The results are discussed in terms of the packing parameters, which indicate that the phase behaviour of the thermotropic tyrosine-based ILCs shows analogies to those of lyotropic liquid crystals. [ABSTRACT FROM AUTHOR]

A homologous series of tri-, di- and monocarbosilane mesogens with a 5-phenylpyrimidine core and a chiral (S,S)-2,3-difluorohexyloxy chain were synthesized and characterized. We show that shortening the carbosilane end-group has a detrimental effect on ‘de Vries-like’ properties, causing an increase in reduction factor R from 0.17 for the tricarbosilane QL32-6 to 0.38 for the monocarbosilane QL34-6, both at the point of maximum layer contraction upon transition from the orthogonal SmA* to the tilted SmC* phase. This increase in R correlates with an increase in birefringence Δn, a broadening in the SmA* temperature range and a decrease in optical tilt angle ϑopt in the SmC* phase, which are all consistent with an increase in orientational order and a decrease in lamellar order. The electroclinic effect (ECE) in the SmA* phase decreases with decreasing length of the carbosilane end-group, which is consistent with previous observations of high ECE in ‘de Vries-like’ liquid crystals. On the other hand, spontaneous polarization PS measurements suggest that polar ordering in the SmC* phase is not strongly dependent on R. [ABSTRACT FROM AUTHOR]

In some liquid crystal (LC) mixtures of bent-core host molecules that form helical nanofilaments (HNFs) and chiral, rod-shaped molecular guests, the spontaneous chirality of the HNFs is not influenced by the guest handedness. In other mixtures, the filaments become homochiral, responding to the handedness of the guest. We show that the important distinction between these two behaviours is the solubility of the guest material in the HNF phase. In our experiments, chiral LC mesogens doped into the HNF phase result in an enantiomeric imbalance and sometimes change the phase sequence on cooling from the isotropic melt. [ABSTRACT FROM PUBLISHER]

Gelled complex fluids are soft materials in which the microstructure of the complex fluid is combined with the mechanical stability of a gel. To obtain a gelled complex fluid one either adds a gelator to a complex fluid or replaces the solvent in a gel by a complex fluid. The most prominent example of a 'natural' gelled complex fluid is the cell. There are various strategies by which one can form a gelled complex fluid; one such strategy is orthogonal self-assembly, that is, the independent but simultaneous formation of two coexisting self-assembled structures within one system. The aim of this Review is to describe the structure and potential applications of various man-made gelled complex fluids and to clarify whether or not the respective system is formed by orthogonal self-assembly. [ABSTRACT FROM AUTHOR]

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