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Liquid-crystal materials exhibiting up to three nematic phases are reported. Dielectric response measurements show that while the lower temperature nematic phase has ferroelectric order and the highest temperature nematic phase is apolar, the intermediate phase has local antiferroelectric order. The modification of the molecular structure by increasing the number of lateral fluorine substituents leads to one of the materials showing a direct isotropic- ferronematic phase transition.

The inclusion of secondary and tertiary benzanilide-based mesogenic groups into liquid crystal dimers is reported as a means to develop new materials. Furthermore, substitution at the nitrogen atom is shown to introduce an additional synthetic 'handle' to modify the molecular structure of the tertiary materials. The design of these materials has proved challenging due to the strong preferences of 3° benzanilides for the E amide conformation. In this work, lateral substitution is used to modify the conformational preferences of the amide linkage and promote liquid crystallinity for a series of N-methyl benzanilide dimers. As the proportion of the E conformer decreases, the nematic-isotropic transition temperatures increase, and enantiotropic nematic behaviour is observed. We also report the synthesis and characterisation of the analogous 2° benzanilide-based materials, which show nematic and twist-bend nematic behaviour. This approach highlights the effects that seemingly small structural modifications, such as the inclusion and position of a methyl group, can have on molecular shape and hence, liquid crystalline behaviour.

ObjectiveWork-related musculoskeletal disorders in ENT surgeons are common and detrimental, yet few are aware of preventative measures. We evaluate the evidence for interventions to prevent work-related musculoskeletal disorders in ENT surgeons.MethodA systematic search of databases up to 8 June 2021 was performed using Preferred Reporting Items for Systematic Review and Meta-Analyses guidelines and predetermined inclusion criteria.ResultsSeven prospective cohort studies and 2 case series were identified (51 participants). Interventions included novel equipment (n= 3), patient positioning (n= 2), clinician positioning (n= 3) and operative technique (n= 1). Five studies reported Rapid Upper Limb Assessment scores as outcome measures of strain. Strain decreased when adopting a favourable operating posture, using a supportive chair and keeping patients supine for clinic procedures.ConclusionA small number of low-quality studies were identified. Modifiable risk factors exist, and ergonomic education may help prevent work-related musculoskeletal disorders. Further studies with longer term follow up are required.

A selection of pyrene-based liquid crystal dimers have been prepared, containing either methylene-ether or diether linked spacers of varying length and parity. All the diether linked materials, CBOnO.Py (n=5, 6, 11, 12), exhibit conventional nematic and smectic A phases, with the exception of CBO11O.Py which is exclusively nematic. The methylene-ether linked dimer, CBnO.Py, with an even-membered spacer (n=5) was solely nematogenic, but odd-members (n=6, 8, 10) exhibited both nematic and twist-bend nematic phases. Replacement of the cyanobiphenyl fragment by cyanoterphenyl giving CT6O.Py, gave elevated melting and nematic-isotropic transition temperatures, and SmA and SmCA phases were observed on cooling the nematic phase. Intermolecular face-to-face associations of the pyrene moieties drive glass formation, and all these materials have a glass transition temperature at or above room temperature. The stability of the glassy twist-bend nematic phase allowed for its study using AFM, and the helical pitch length, PTB , was measured as 6.3 and 6.7 nm for CB6O.Py and CB8O.Py, respectively. These values are comparable to the shortest pitch of a twist-bend nematic phase measured to date.

The syntheses and characterisation of the first ten homologues of the (34-[6-(4-{(E)-[(4-alkylphenyl)imino]methyl}phenoxy)-hexyl][11,21:24,31-terphenyl]-14-carbonitriles (CT6O.m) are reported. Below the conventional nematic phase, N, a rich smectic polymorphism is observed. CT6O.m homologues with m = 1–9 show a series of up to four smectic phases, namely: an intercalated biaxial smectic Ab phase, a modulated phase made of tilted biaxial SmC layer fragments, a non-tilted biaxial hexatic-type phase termed the SmX phase, and a soft crystalline lamellar phase, SmY. The longest homologue, CT6O.10, exhibits a different sequence of smectic phases below the N phase: an uniaxial SmA phase, a biaxial SmAb phase, a tilted SmC phase, and the soft crystalline SmY phase. The assignment of these phases was confirmed using a combination of polarised optical microscopy, X-ray diffraction and optical birefringence studies. In CT6O.10 only the SmC has an intercalated structure of molecules; while the smectic phases either side show interdigitated molecular packing arrangement. The strong biaxiality of the SmC phase results in an unusual switching mode detected under the application of an electric field, in which by coupling the dielectric anisotropy with the electric field, molecules in cells with planar anchoring reorient to give an optical texture without tilt domains, and the switching is accompanied by a considerable increase in the measured birefringence.

A number of liquid crystal dimers have been synthesised and characterised containing secondary or tertiary (N-methyl) benzanilide-based mesogenic groups. The secondary amides all form nematic phases, and we present the first example of an amide to show the twist-bend nematic (NTB) phase. Only two of the corresponding N-methylated dimers formed a nematic phase and with greatly reduced nematic-isotropic transition temperatures. Characterisation using 2D ROESY NMR experiments, DFT geometry optimisation and X-ray diffraction reveal that there is a change in the preferred conformation of the benzanilide core on methylation, from Z to E. The rotational barrier around the N-C(O) bond has been measured using variable temperature 1H NMR spectroscopy. This dramatic change in shape accounts for the remarkable difference in liquid crystalline behaviour between these secondary and tertiary amide-based materials.

Contrary to dominant debates about Utopia, I do not think it matters whether Thomas More actually believed that ‘communism’ was the solution to social inequality and injustice; what I think is important is that the book raises the question of a different type of society. As I argue in the second part of my article, the power of Utopia, like all radical utopianism, derives not from the production of blueprints; rather, it comes from the stimulation of desire for a ‘happy place’, which can reflect negatively on, and produce discontent within, the here and now. Understood in this way, radical utopianism offers a form of resistance to dominant constructions of reality and our complicity, conscious and unconscious, with them.

The synthesis and characterisation of two homologous series of non-symmetric dimers are reported, the 1-(4-methoxybiphenyl-4ʹ-yl)-6-(4-alkylanilinebenzylidene-4ʹ-oxy)hexanes (MeOB6O.m, m = 1–10) an...

A selection of novel, chiral supramolecular liquid crystals formed by hydrogen-bonding are reported and their phase properties characterised by polarised optical microscopy, X-ray diffraction and resonant soft X-ray diffraction. Their behaviour is compared to that of their achiral analogues. The binary mixture of the bent-shaped, non-mesogenic H-bond acceptor 1OB6OS and chiral H-bond donor (S)-(2-Me)4OBA exhibits chiral nematic (N*) and chiral smectic A (SmA*) phases. Doping the twist-bend nematogenic (NTB) complex 1OB6OS:4OBA with (S)-(2-Me)4OBA in ternary mixtures induces a transition from the N* phase to the chiral twist-bend nematic phase N*TB, the first example seen in a supramolecular liquid crystal. The binary mixture of CB6OS and (S)-(2-Me)4OBA exhibits N* and N*TB phases, with the helical structure of the latter having a periodicity of approximately 2 complex lengths (∼8 nm). The nature of the hydrogen bond is reversed in a binary mixture of the bent-shaped, twist-bend nematogen CB6OBA with (S)-(2-Me)4OBA, and this exhibits the phase sequence N*–N*TB–SmC*–SmX.

An oblique helicoidal cholesteric liquid crystal ${\mathrm{Ch}}_{\mathrm{OH}}$ represents a unique optical material with a single-harmonic periodic modulation of the refractive index and a pitch that can be tuned by an electric or magnetic field in a broad range from submicrometers to micrometers. In this work, we demonstrate that the oblique helicoidal cholesteric doped with azoxybenzene molecules can be tuned by both the electric field and light irradiation. The tuning mechanism is explained by the kinetics of trans-cis photoisomerization of the azoxybenzene molecules. At a fixed voltage, UV irradiation causes a redshift of the reflection peak by more than 200 nm. The effect is caused by an increase of the bend elastic constant of ${\mathrm{Ch}}_{\mathrm{OH}}$ under irradiation. The demonstrated principle has the potential for applications such as smart windows, sensors, tunable lasers, and filters.

An oblique helicoidal cholesteric ChOH represents a unique optical material with a pitch that can be tuned by an electric or magnetic field in a broad range from sub micrometers to micrometers. In this work, we demonstrate that the oblique helicoidal cholesteric doped with azoxybenzene molecules and stabilized by an electric field could also be tuned by light irradiation. At a fixed voltage, UV irradiation causes a redshift of the reflection peak by more than 200 nm. The demonstrated effect has the potential for applications such as smart windows, sensors, tunable lasers, and filters.

The synthesis and characterisation of a new set of azobenzene-based non-symmetric liquid crystal dimers, the 1-(4-substitutedazobenzene-4ʹ-yloxy)-6-(4-methoxybiphenyl-4ʹ-yl)hexanes (MeOB6OABX), that exhibit the twist-bend nematic phase, NTB, is described. The terminal substituents are methyl, methoxy, ethyl, butyl, butoxy, and nitrile. All six dimers exhibit both the NTB and conventional nematic, N, phases. The identification of the NTB phase was performed using polarised light microscopy and confirmed for binary mixtures with a standard twist-bend nematogen 1,7-bis-4-(4ʹ-cyanobiphenyl) heptane (CB7CB). The transitional behaviour of the MeOB6OABX dimers is compared with that of the corresponding ether-linked 1-(4-substitutedazobenzene-4ʹ-yloxy)-6-(4-methoxybiphenyl-4ʹ-yloxy)pentanes, MeOBO5OABX, all of which exhibit a conventional nematic phase. In addition, the nitrile-substituted MeOBO5OABCN shows the NTB phase. The behaviour of these non-symmetric dimers is also compared to that of the corresponding symmetric dimers. Differences in the transitional properties between these sets of new materials are accounted for in terms of not only molecular shape but also other factors including the strength of the mixed mesogen interaction.

Acknowledgements E.G. and D.P. acknowledge the support of the National Science Centre (Poland): (Grant Number 2016/22/A/ST5/00319). R.W. gratefully acknowledges The Carnegie Trust for the Universities of Scotland for funding the award of a PhD scholarship.

The synthesis and characterisation of two series of cyanobiphenyl-based liquid crystal dimers containing sulfur links between the spacer and mesogenic units, the 4ʹ-[1,ω-alkanediylbis(thio)]bis-[1,1ʹ-biphenyl]-4-carbonitriles (CBSnSCB), and 4ʹ-({ω-[(4ʹ-cyano[1,1ʹ-biphenyl]-4-yl)oxy]alkyl}thio)[1,1ʹ-biphenyl]-4-carbonitriles (CBSnOCB) are described. The odd members of both series show twist-bend nematic and nematic phases, whereas the even members exhibit only the nematic phase. An analogous cyanoterphenyl-based dimer, 34-{6-[(4ʹ-cyano[1,1ʹ-biphenyl]-4-yl)thio]-hexyl}[11,21:24,31-terphenyl]-14-carbonitrile (CT6SCB), is also reported and shows enantiotropic NTB and N phases. The transitional properties of these dimers are discussed in terms of molecular curvature, flexibility and biaxiality. The same molecular factors also influence the birefringence of nematic phases. Resonant X-ray scattering studies of the twist-bend nematic phase at both the carbon and sulfur absorption edges were performed, which allowed for the determination of critical behaviour of the helical pitch at the transition to the nematic phase, the behaviour was found to be independent of molecular structure. It was also observed that despite the different molecular bending angle and flexibility, in all compounds the helical pitch length far from the N-NTB transition corresponds to 4 longitudinal molecular distances.

Significance The twist–bend (TB) liquid crystal phase is the newest nematic phase, having only been identified in 2011. Still, there are many outstanding mysteries about the nature of its nanoscale organization and behavior. We elucidate how the number of monomer units in a linear TB oligomer influences the structure of its nanoscale helix, an important TB phase structure–property relationship. While a TB dimer exhibits a temperature-dependent variation of its helix pitch, the analogous trimer features a temperature-independent helix pitch considerably shorter than that of the dimer and other known TB materials. This study illuminates the scope of possible variations that manifest in the TB phase and represents a substantial step in controlling its nanoscale behavior for technological applications., We synthesized the liquid crystal dimer and trimer members of a series of flexible linear oligomers and characterized their microscopic and nanoscopic properties using resonant soft X-ray scattering and a number of other experimental techniques. On the microscopic scale, the twist–bend phases of the dimer and trimer appear essentially identical. However, while the liquid crystal dimer exhibits a temperature-dependent variation of its twist–bend helical pitch varying from 100 to 170 Å on heating, the trimer exhibits an essentially temperature-independent pitch of 66 Å, significantly shorter than those reported for other twist–bend forming materials in the literature. We attribute this to a specific combination of intrinsic conformational bend of the trimer molecules and a sterically favorable intercalation of the trimers over a commensurate fraction (two-thirds) of the molecular length. We develop a geometric model of the twist–bend phase for these materials with the molecules arranging into helical chain structures, and we fully determine their respective geometric parameters.

The syntheses and characterisation of the first ten homologues of the 1-(4-cyanobiphenyl-4'-yl)-6-(4-alkylanilinebenzylidene-4'-oxy)hexanes (CB6O.m) are reported. All ten members of the series exhibit an enantiotropic nematic, N, phase, and a monotropic twist-bend nematic, NTB, phase. Only CB6O.10 shows a smectic phase. The assignment of both nematic phases was confirmed using X-ray diffraction. For short chain lengths (m = 1-6) the local packing in both nematic phases is an intercalated arrangement, for intermediate chain lengths a frustrated local structure is seen and for the longest chain length, a bilayer arrangement is observed. This change in the local structure on increasing m has no apparent effect on the stability of either nematic phase, and TNTBN and TNI show a regular dependence on m. Specifically, TNTBN and TNI decrease on increasing m and superimposed upon this is a weak odd-even effect in which the odd members show the higher values. TNI decreases more rapidly than TNTBN on increasing m such that the ratio TNTBN/TNI increases. The lower temperature liquid crystal phase shown by 1-(4-cyanobiphenyl-4'-yloxy)-5-(4-butylanilinebenzylidene-4'-oxy)pentane (CBO5O.4) is reassigned as a twist-bend nematic phase. The transitional properties of the CB6O.m, CB6O.Om and CBO5O.m series are compared.

Using a photo-responsive dimer exhibiting the transition between nematic (N) and twist-bend nematic (NTB) phases, we prepared spherical cap-shaped droplets on solid substrates exposed to air. The internal director structures of these droplets vary depending on the phase and on the imposed boundary conditions. The structural switching between the N and NTB phases was successfully performed either by temperature control or by UV light-irradiation. The N phase is characterized by an extremely small bend elastic constant K3, and surprisingly, we found that the droplet-air interface induces a planar alignment, in contrast to that seen for typical calamitic liquid crystals. As a consequence, the director configuration was stabilized in a structure substantially different from that normally found in conventional nematic liquid crystalline droplets. In the twist-bend nematic droplets characteristic structures with macroscopic length scales were formed, and they were well controlled by the droplet size. These results indicated that a continuum theory is effective in describing the stabilization mechanism of the macroscopic structure even in the twist-bend nematic liquid crystal droplets exhibiting director modulations on a scale of several molecular lengths.

Achiral mesogenic molecules are shown to be able to spontaneously assemble into liquid crystalline smectic phases having either simple or double-helical structures. At the transition between these phases, the double-helical structure unwinds. As a consequence, in some temperature range, the pitch of the helix becomes comparable to the wavelength of visible light and the selective reflection of light in the visible range is observed. The photonic bandgap phenomenon is reported for achiral liquid crystals.