R.O. Vergara-Toloza

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.

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.

Phase characterization of LC (meth)acrylic monomers based on ω-hexyloxy- and ω-undecyloxy-salicylaldimine groups with different alkoxy tail substitutions

The synthesis and phase characterization of three homologous series of liquid crystalline acrylic and methacrylic monomers, consisting of 21 new compounds are presented. They are based on ω-hexyloxy- and ω-undecyloxysalicylaldimine groups with different alkoxy tail substitutions. The liquid crystalline materials were characterized by polarizing optical microscopy and differential thermal analysis. Smectic A and tilted smectic C phases were observed in the compounds. Near the transition to the isotropic, a narrow nematic phase, coexisting with the smectic A phase, was detected for the pentyloxy and hexyloxy derivatives in the M11 and A11 series. In case of M11R11 and M11R12 only a tilted smectic C phase was detected. The clearing point was comparable for all series, around 100°C.

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.

Design of highly polarized achiral mesogenic composites

The synthesis of one homologous series of methacrylate monomers and their polymers was carried out to observe the dependence between the polarization and some structural aliphatic features. Investigations of the thermoanalytical, structural and pyroelectric properties of the composites were carried out. All investigated samples showed a typical non-linear behavior of the pyroelectric response under an applied electric field. The saturation voltage was around 12.5 V μm−1 on average. By increasing the length of the aliphatic tail of the homologous series a change from antiferroelectric to ferroelectric behavior was observed. As a result of this study, we were able to control the ferroelectric or antiferroelectric properties in mixtures of achiral polymer–monomer composites taking into account the appropriate length of the aliphatic alkyl chain of the components in the mixture.

Studies of first‐ and second‐order phase transitions in LC methacrylic monomers based on the ω‐hexyloxysalicylaldimine group

The synthesis and phase characterization of two liquid crystalline methacrylic monomers based on the ω‐hexyloxysalicylaldimine group with octyl and decyloxy chain substitutions is presented. The liquid crystalline materials were characterized by polarizing optical microscopy, differential thermal analysis and X‐ray diffractometry. Nematic and tilted smectic C phases were observed in the compounds. Their liquid crystalline properties where compared with previously studied samples of homologous compounds. In contrast to previous results, this structural modification induces pronounced enantiotropic first‐order phase transitions between nematic and smectic C mesophases. A correlation between the phase transition behaviour and structural features of the sample is included.

Conformational constraint in ferroelectric liquid crystals incorporating a pyrrolidine‐type ring: FLC materials comprising parallel dipolar moments

Ferroelectric liquid crystals bearing a chiral pyrrolidine‐type ring were prepared using (–)‐(S)‐malic acid as a building block. The compounds were characterized using the thermal analysis techniques of DSC and POM, electrical measurements and temperature‐dependent XRD. Samples showed moderate spontaneous polarization values (P S) with helical pitches of about 2.997 µm and an average tilt angle of 16.2° for the SmC* planes. Conformational analysis of the chiral pyrrolidinol subunit and of all of the mesogenic targets was performed using several quantum methods including large basis sets and different treatments of electron correlation in order to correlate experimental results and theoretical predictions. For the most stable conformations, a very small dipole moment component perpendicular to the tilt plane was found which, according to the Boulder model, may be responsible for the moderate PS values obtained.