Twist-bend nematic phase in cyanobiphenyls and difluoroterphenyls bimesogens

ABSTRACT

The paper reviews assignment of the low-temperature nematic phase observed in simple bimesogenic or dimeric systems based on cyanobiphenyls and difluoroterphenyls to the twist-bend nematic phase, N_TB, using a range of experimental techniques. These include DSC, X-rays, Polarising Microscopy, electro-optics, birefringence and measurements of the electroclinic effect arising from flexoelectricity. An emphasis is laid on the observations of the chiral domains of opposite handedness at zero field in an otherwise achiral liquid crystalline system in this phase. These observations are a direct consequence of the structure of the twist-bend phase predicted by Ivan Dozov for achiral bent core molecules. The paper reviews the electro-optic phenomena and the observed electroclinic effect and how these observations assign it as the N_TB phase. Results of the nanoscale helical pitch measurements using freeze-fracture microscopy are reviewed and discussed briefly. Results of the measurements of elastic constants especially close to the N–N_TB transition are also reviewed.     

Nematic tribenzosilatranes

The linkage of benzylsilatrane groups to laterally functionalized mesogens allows the investigation of molecular systems which contain propeller shaped mesogens and exhibit nematic phase behaviour.     

Calorimetrie

Ohne Zusammenfassung     

Design, synthesis, and characterization of mesogenic amine-capped nematic gold nanoparticles with surface-enhanced plasmonic resonances

The use of the liquid-crystalline state to control the assembly of large (>5 nm) gold nanoparticles (NPs) is of considerable interest because of the promise of novel metamaterial properties of such systems. Here we report on a new approach for the preparation of large nematic gold NPs using a bifunctional capping agent that enables control over the particle size and serves as a linkage for subsequent functionalization with mesogenic groups. Properties of the NPs were characterized by HRTEM, NMR, DSC, TGA, UV/vis, OPM, and XRD studies. The results confirmed the formation of a stable nematic mesophase above 37.5 °C for NPs in the 6-11 nm size range.     

Effects of adiabatic, relativistic, and quantum electrodynamics interactions on the pair potential and thermophysical properties of helium

The adiabatic, relativistic, and quantum electrodynamics (QED) contributions to the pair potential of helium were computed, fitted separately, and applied, together with the nonrelativistic Born-Oppenheimer (BO) potential, in calculations of thermophysical properties of helium and of the properties of the helium dimer. An analysis of the convergence patterns of the calculations with increasing basis set sizes allowed us to estimate the uncertainties of the total interaction energy to be below 50 ppm for interatomic separations R smaller than 4 bohrs and for the distance R = 5.6 bohrs. For other separations, the relative uncertainties are up to an order of magnitude larger (and obviously still larger near R = 4.8 bohrs where the potential crosses zero) and are dominated by the uncertainties of the nonrelativistic BO component. These estimates also include the contributions from the neglected relativistic and QED terms proportional to the fourth and higher powers of the fine-structure constant α. To obtain such high accuracy, it was necessary to employ explicitly correlated Gaussian expansions containing up to 2400 terms for smaller R (all R in the case of a QED component) and optimized orbital bases up to the cardinal number X = 7 for larger R. Near-exact asymptotic constants were used to describe the large-R behavior of all components. The fitted potential, exhibiting the minimum of -10.996 ± 0.004 K at R = 5.608 0 ± 0.000 1 bohr, was used to determine properties of the very weakly bound (4)He(2) dimer and thermophysical properties of gaseous helium. It is shown that the Casimir-Polder retardation effect, increasing the dimer size by about 2 ? relative to the nonrelativistic BO value, is almost completely accounted for by the inclusion of the Breit-interaction and the Araki-Sucher contributions to the potential, of the order α(2) and α(3), respectively. The remaining retardation effect, of the order of α(4) and higher, is practically negligible for the bound state, but is important for the thermophysical properties of helium. Such properties computed from our potential have uncertainties that are generally significantly smaller (sometimes by nearly two orders of magnitude) than those of the most accurate measurements and can be used to establish new metrology standards based on properties of low-density helium.     

A protein-polymer hybrid mediated by DNA

Protein-polymer hybrids (PPHs) represent an important and rapidly expanding class of biomaterials. Typically in these hybrids the linkage between the protein and the polymer is covalent. Here we describe a straightforward approach to a noncovalent PPH that is mediated by DNA. Although noncovalent, the DNA-mediated approach affords the highly specific pairing and assembly properties of DNA. To obtain the protein-DNA conjugate for assembly of the PPH, we report here the first direct copper catalyzed azide-alkyne cycloaddition-based protein-DNA conjugation. This significantly simplifies access to protein-DNA conjugates. The protein-DNA conjugate and partner polymer-DNA conjugate are readily assembled through annealing of the cDNA strands to obtain the PPH, the assembly of which was confirmed via dynamic light scattering and fluorescence spectroscopy.     

Research problem: indefinite inner product normal matrices

Several open research problems are formulated concerning normal matrices with respect to indefinite inner products.     

Detecting columnar deformations in a supermesogenic octapode by proton NMR relaxometry

We used proton ( ¹H nuclear magnetic relaxation (NMR) dispersions to study the molecular dynamics in the isotropic phase and mesophases (nematic and columnar hexagonal) of a supermesogenic octapode formed by laterally connecting calamitic mesogens to an inorganic silsesquioxane cube through flexible spacers. The dispersions of the spin-lattice relaxation time (T₁) are interpreted through relaxation mechanisms used for the study of molecular dynamics in low-molar-mass liquid crystals but adapted to the case of liquid crystalline supermolecules. At high frequencies (above 10MHz) the behaviour of the T₁ with the Larmor frequency is similar for all phases and is ascribed to local reorientations and/or rotations. At intermediate and low frequencies (below 10MHz) our results show notable differences in the T₁ behaviour with respect to the mesophases. The nematic (N) and isotropic (Iso) phases’ low-frequency results are similar and are interpreted for both phases in terms of order director fluctuations (ODF), revealing that even in the isotropic phase local nematic order is detected by proton NMR relaxometry. Local nematic order in the Iso phase is interpreted in terms of the presence of nematic cybotactic clusters induced by the interdigitation of mesogens that is promoted by the silsesquioxane octapode molecular structure. In the columnar hexagonal (Col _h phase, the T₁ dispersions show that elastic columnar deformations (ECD) dominate the nuclear magnetic relaxation below 10MHz. This result shows that the columnar packing of the octapode clearly restricts the collective fluctuations of the mesogenic units inspite of their local nematic order.