Different liquid crystalline phases with long-range orientational but not positional order, so-called nematic phases, are scarce. New nematic phases are rarely discovered, and such an event inevitably generates much interest. Here, we describe a transition from a uniaxial to a novel nematic phase characterized by a periodic splay modulation of the director. In this new nematic phase, defect structures not present in the uniaxial nematic phase are observed, which indicates that the new phase has lower symmetry than the ordinary nematic phase. The phase transition is weakly first order, with a significant pretransitional behavior, which manifests as strong splay fluctuations. When approaching the phase transition, the splay nematic constant is unusually low and goes towards zero. Analogously to the transition from the uniaxial nematic to the twist-bend nematic phase, this transition is driven by instability towards splay orientational deformation, resulting in a periodically splayed structure. And, similarly, a Landau-de Gennes type of phenomenological theory can be used to describe the phase transition. The modulated splay phase is biaxial and antiferroelectric.

Ferroelectric ordering in liquids is a fundamental question of physics. Here, we show that ferroelectric ordering of the molecules causes formation of recently reported splay nematic liquidcrystalline phase. As shown by dielectric spectroscopy, the transition between the uniaxial and the splay nematic phase has the characteristics of a ferroelectric phase transition, which drives an orientational ferroelastic transition via flexoelectric coupling. The polarity of the splay phase was proven by second harmonic generation (SHG) imaging, which additionally allowed for determination of the splay modulation period to be of the order of 5 -10 microns, also confirmed by polarized optical microscopy. The observations can be quantitatively described by a Landau-de Gennes type of macroscopic theory. SI A. Material RM734 was synthesized according to Ref.[1] and additionally purified as described in Ref. [2]. As determined by means of differential scanning calorimetry phase transition temperatures have been determined to be: isotropic to nematic TIN= 187.9 °C, nematic to second nematic transition at TNNs = 132.7 °C, and a melting point at Tm = 139.8 °C. We used the Gaussian G09e01 suite of programs [3] to determine the B3LYP/6-31G(d) minimized geometry of RM734 shown in Fig.1. The molecular dipole moment calculated by the B3LYP/6-31G(d) level of DFT is of 11.3748D and oriented almost along the molecular long axis.

By dynamic light scattering we have studied suspensions of ferrimagnetic maghemite (gamma-Fe2O3) nanoparticles in n -decane with attractive interparticle interaction. The measurements in the suspensions of different concentrations ranging from 0.21 to 25.8 wt % have been compared in zero external field and in the magnetic field of 270 mT. In all samples well-defined relaxation process was observed. In the absence of an external field the suspensions were homogeneous, while in the magnetic field most of the suspensions undergo phase separation in a needlelike islands of a very dense suspension surrounded by a dilute suspension. The underfield dynamical behavior is found to be anisotropic and diffusive in both directions at low concentration. For the more concentrated sample, in the direction parallel to the external field, it remains diffusive with a larger diffusion coefficient while it is not so in the perpendicular direction, in which the mean-squared displacement grows faster than linearly with time and the dependence of the relaxation rate on the scattering vector q is not quadratic. In this direction the dynamics of the system present similar features as glasses or gels close to the dynamical arrest.

Liquid crystal elastomers (LCEs) can undergo large reversible contractions along their nematic director upon heating or illumination. A spatially patterned director within a flat LCE sheet, thus, encodes a pattern of contraction on heating, which can morph the sheet into a curved shell, akin to how a pattern of growth sculpts a developing organism. Here, we consider theoretically, numerically, and experimentally patterns constructed from regions of radial and circular director, which, in isolation, would form cones and anticones. The resultant surfaces contain curved ridges with sharp V-shaped cross sections, associated with the boundaries between regions in the patterns. Such ridges may be created in positively and negatively curved variants and, since they bear Gauss curvature (quantified here via the Gauss–Bonnet theorem), they cannot be flattened without energetically prohibitive stretch. Our experiments and numerics highlight that, although such ridges cannot be flattened isometrically, they can deform isometrically by trading the (singular) curvature of the V angle against the (finite) curvature of the ridge line. Furthermore, in finite thickness sheets, the sharp ridges are inevitably non-isometrically blunted to relieve bend, resulting in a modest smearing out of the encoded singular Gauss curvature. We close by discussing the use of such features as actuating linear features, such as probes, tongues, and grippers. We speculate on similarities between these patterns of shape change and those found during the morphogenesis of several biological systems.

We investigated the effect of a photovoltaic field generated on the surface of iron-doped lithium niobate crystals on sessile droplets of a ferroelectric nematic liquid crystalline and a standard nematic liquid crystalline material present on this surface. When such an assembly is illuminated with a laser beam, a wide range of dynamic phenomena are initiated. Droplets located outside the laser spot are dragged in the direction of the illuminated area, while droplets located inside the illuminated region tend to bridge each other and rearrange into tendril-like structures. In the ferroelectric nematic phase (NF), these processes take place via the formation of conical spikes evolving into jet streams, similar to the behavior of droplets of conventional dielectric liquids exposed to overcritical electric fields. However, in contrast to traditional liquids, the jet streams of the NF phase exhibit profound branching. In the nematic phase (N) of both the ferroelectric nematic and the standard nematic material, dynamic processes occur via smooth-edged continuous features typical for conventional liquids subjected to under-critical fields. The difference in dynamic behavior is attributed to the large increase of dielectric permittivity in the ferroelectric nematic phase with respect to the dielectric permittivity of the nematic phase.

In this work, we demostrate the preparation of low cost High Refractive Index polystyrene-sulfur nanocomposites in one step by combining inverse vulcanization and melt extrusion method. Poly(sulfur-1,3-diisopropenylbenzene) (PS-SD) copolymer nanoparticles (5 to 10 wt%) were generated in the polystyrene matrix via in situ inverse vulcanization reaction during extrusion process. Formation of SD copolymer was confirmed by FTIR and Raman spectroscopy. SEM and TEM further confirms the presence of homogeneously dispersed SD nanoparticles in the size range of 5 nm. Thermal and mechanical properties of these nanocomposites are comparable with the pristine polystyrene. The transparent nanocomposites exhibits High Refractive Index n = 1.673 at 402.9 nm and Abbe’y number ~ 30 at 10 wt% of sulfur loading. The nanocomposites can be easily processed into mold, films and thin films by melt processing as well as solution casting techniques. Moreover, this one step preparation method is scalable and can be extend to the other polymers.

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