Eduardo A. Soto-Bustamante

Nanoconfinement of guest materials by helical nanofilament networks of bent-core mesogens

The helical nanofilament (HNF) liquid crystal phase is a complex, hierarchical self-assembly in which bent-core molecules cooled from the isotropic melt form dense periodic arrays of nanoscale filaments of twisted smectic layers, a structure driven by an inherent tendency of the layers to be locally saddle-splayed. Here we report the results of a study of mixtures of an HNF-forming bent-core liquid crystal with a variety of organic guest molecules, showing that the high temperature, isotropic phase is completely mixed but that upon cooling the filaments form and grow, expelling the guest material from their internal volume. The nanofilaments form a network which acts as a porous nanoconfinement medium of large internal area (∼100 m2 cm−3), with the guest material confined to nanoscale interstitial volumes between the filaments. Such helical nanofilament networks represent a robust platform for potential applications in chiral separations, asymmetric synthesis, and photonic metamaterials.

Novel chiral calamitic liquid crystalline oxadiazoles as ferroelectric materials

Novel liquid crystalline materials based on chiral calamitic 1,2,4‐ and 1,3,4‐oxadiazole derivatives were synthesized and their thermotropic mesomorphism investigated by polarizing optical microscopy and differential scanning calorimetry. The structures of their smectic phases were investigated by X‐ray diffraction. The existence of ferroelectric properties in the smectic C phase was also studied.

Phase characterization of two homologous series of LC methacrylic monomers based on ω-hexyl- and ω-butyl-oxysalicylaldimine groups with different alkoxy tail substitutions

The phase characterization of two homologous series of liquid crystalline methacrylic monomers based on ω-hexyl- and ω-butyloxysalicylaldimine groups, with different alkoxy tails, is presented. The liquid crystalline materials were characterized by polarising optical microscopy, differential scanning calorimetry, differential thermal analysis, and X-ray diffraction. All the monomers exhibit the simultaneous occurrence of smectic A and C phases. When the alkyl chain is short, a narrow nematic phase is observed, leading to an I-N-SmA-SmC phase sequence.

Liquid crystalline side chain methacrylic azo containing polymers

This paper describes the synthesis and characterisation of methacrylic liquid crystalline side chain polymer containing azo group, with (PM6OAn) and without (PM6An) hydroxyl group. The characterisation was done by using a polarised light microscope (PLM), differential thermal analysis (DTA), and X-ray diffractometry. All compounds developed bilayer smectic phase, with a certain degree of interdigitation between the layers. Poly[{3-hydroxy-4-[(E)-(4-octyloxyphenyl)diazenyl]phenoxy}hexyl]-2-methyl-prop-2-enoate (PM6OA8) exhibits a smectic A phase, whereas the other polymers show a SmC phase. Pyroelectric investigations show only an antiferroelectric behaviour for poly [{3-hydroxy-4-[(E)-(4-dodecyloxyphenyl)diazenyl]phenoxy}hexyl]-2-methylprop-2-enoate (PM6OA12) and a paraelectric behaviour for PM6OA8, poly[{4-[(E)-(4-dodecyloxyphenyl)diazenyl]phenoxy}hexyl]-2-methylprop-2-enoate (PM6A12) and poly [{4-[(E)-(4-octyloxyphenyl) diazenyl] phenoxy} hexyl]-2-methylprop-2-enoate (PM6A8). Finally, the E-Z photoisomerisation of the chromophores in solution was probed to exist in PM6A12 and PM6A8.

Synthesis and characterization of pyroelectric nanocomposite formed of BaTiO3 nanoparticles and a smectic liquid crystal matrix

This article combines the properties of both types of ferroelectric materials (inorganic ceramic and liquid crystal), to obtain a plastic composite exhibiting high polarization. To realize this target, a liquid crystalline nanocomposite was prepared comprising a polymer (PM6R10) and a monomer (M6R6) mixture in a 2 : 1 ratio, PM10M6 and BaTiO3 nanoparticles (NpBT). To prepare the nanomaterials, we used the calcinations method of a gel precursor. By studying the dependence of the morphological and structural characteristics with the annealing time at 1000°C, we obtained a product that possess the properties suitable for the purpose of this study. Then to PM10R6, NpBT were added at a concentration of 5%, with and without oleic acid (OA). Measurement of the pyroelectric signal reveals that the addition of NpBT significantly increases the pyroelectric response of the material compared to the original composite. However, when adding OA as the compatibilizer, the pyroelectric signal and therefore their polar property practically disappears.

Pyroelectric effect in ultrathin layers of achiral mesogenic composites

The pyroelectric properties of the solid mixtures of achiral liquid crystalline polymers with their monomers were studied. The composites were fabricated in a thin film form (less than 1 μm) by spin-coating technique. The maximum value of the current responsivity being 0.67 μA/W has been obtained for optimum monomer/polymer ratio of 33%:67% by weight. The pyroelectric voltage was measured in the frequency range from 10 Hz up to 250 kHz. The figure of merit for the composite at room temperature is about 0.8 nC/cm2 K, which is more than twice higher than that of polyvinylidene fluoride with trifluroethylene 70%:30%.

X-ray study of bilayered tilted structures in liquid crystalline side chain methacrylic polymers

The synthesis and measurement of thermodynamic properties of six methacrylate-based polymers were undertaken to observe the relationship between structural aliphatic features and mesophase properties. X-ray measurements on some of the polymers investigated show, as expected, the existence of bilayered smectic phases SmC2 and SmAd. Taking into account our previous results, an interesting trend in the tilt angle was found that might be related to the difference in alkyl chain substitution.

Light sensitive antiferroelectric achiral copolymers

Five copolymers were prepared by polymerization of azo-benzene methacrylate monomers in solution using AIBN as initiator. The mesophases were observed by a polarizing light microscope which showed tilted smectic C phases for almost all samples. One of them shows just one orthogonal smectic A2 phase. The X-ray diffraction patterns reveal the existence of bilayer smectic C2 mesophases. The spontaneous polarization and pyroelectric response are reported showing an antiferroelectric behaviour for three of the copolymers. The polar phase has to do with a preferable arrangement of side chains in a syndiotactic fashion, which promotes the formation of anticlinicity in the polymer net. We probe that it is possible to induce orientation of the chromophores subjected to irradiation with UV/Vis light and that it is proportional to the amount of monomers without the OH group within the copolymers. This is so far a unique manifestation of polar ordering due to the syndiotactic lateral distribution of mesogens bearing an OH group in a tilted smectic C2 phase.

Passive amplification of the pyroelectric current in thin films on a heat-conducting substrate

We show both theoretically and experimentally that passive amplification of the pyroelectric current takes place when modulated radiation is recorded by a pyroelectric detector in some range of modulation frequencies. The amplification effect manifests itself in the fact that the current generated by a thin pyroelectric film lying on a massive heat-conducting substrate exceeds that in a freely suspended film. We use a ferroelectric 70:30 P(VDF-TrFE) copolymer, a crystalline guanidine pyroelectric, and a 70:30 composition of an achiral liquid-crystal polymer and its monomer PM6R14n-M6R14n to illustrate the frequency dependence of the pyroelectric current.

Side chain liquid crystalline composites, occurrence of interdigitated bilayer smectic C phases

We report on the results of X-ray investigations in two series of polymer monomer composites, PM6Rm-33 and PMnR12-33, which consist of mixtures of achiral liquid crystalline side chain polymers and their monomers. These mixtures present a unique integration of monomer in the polymeric base which assists in modifying their properties and forming homogenous composites. X-ray measurements for all the investigated composites indicate the existence of bilayered smectic C phases (SmC2). In several composites, the interlayer distance of the SmC2 phase abnormally increases with cooling; this is associated with the aliphatic interdigitation at the tail-to-tail interface being more prominent when longer aliphatic tails are present.