Damian Pociecha

Ideal Liquid Crystal Display Mode Using Achiral Banana-Shaped Liquid Crystals

We have demonstrated a totally new liquid crystal display (LCD) mode using a smectic A-like phase of banana-shaped molecules. An in-plane electric field was applied to homeotropically aligned cells, resulting in fast polarization reorientation and the associated birefringence. The reported LCD mode has all the advantages of the existing LCD modes, such as vertical alignment (VA), in-plane switching (IPS), ferroelectric LC (FLC) or antiferroelectric LC (AFLC) and V-shaped switching (VS) modes; namely, fast response of the order of 100 µs, high contrast ratio (3000:1), wide viewing angle, continuous gray level, and small threshold voltage. These performances originate from the cooperative motion of bent molecules with quasi-long-range order of dipoles based on a two-dimensional Langevin process.

Do the short helices exist in the nematic TB phase

Dimeric compounds forming twist-bend nematic, Ntb, phase show unusual optical textures related to the formation of arrays of focal conic defects (FCDs). Some of the focal conics exhibit submicron internal structure with 8 nm periodicity, which is very close to that found in the crystalline phase of the material, that might suggest surface freezing.

A Twist-Bend Nematic (NTB) Phase of Chiral Materials†

New chiral dimers consisting of a rod-like and cholesterol mesogenic units are reported to form a chiral twist-bend nematic phase (NTB *) with heliconical structure. The compressibility of the NTB phase made of bent dimers was found to be as large as in smectic phases, which is consistent with the nanoperiodic structure of the NTB phase. The atomic force microscopy observations in chiral bent dimers revealed a periodicity of about 50 nm, which is significantly larger than the one reported previously for non-chiral compounds (ca. 10 nm).

Theoretical and experimental study of the intermediate Sm CFI 2* and the Sm CFI 1* phases in antiferroelectric liquid crystals

Within the new phenomenological model of antiferroelectric liquid crystals, structures of the two phases, the Sm CFI2* and the Sm CFI1* that appear in the temperature range between the Sm C* and the Sm CA* phase, are found. The structure of the Sm CFI2* and the Sm CFI1* phases is consistent with extensive optical, electro-optic, and dielectric measurements performed on the liquid crystal R-10OTBBB1M7, for which resonant x-ray scattering studies have previously proven that these two phases have the three-layer (Sm CFI1*) and the four-layer (Sm CFI2*) periodic structure, respectively. The biaxiality of the four-layer structure of the Sm CFI2* phase is directly observed experimentally for the first time at the temperature where the optical pitch is unwound. The theoretical model allows for experimentally consistent phase sequence, the order of transitions, and the temperature dependence of optical properties including the optical helicoidal modulation inversion within the temperature range of the Sm CFI2* phase.

Multidimensional structures made by gold nanoparticles with shape-adaptive grafting layers

The ability of gold nanoparticles grafted with soft, adaptive organic layers made of two types of thiol molecules, n-alkyl and mesogenic ones, to form spontaneously long-range positionally ordered structures is shown. It was found that molecular structure of mesogenic thiols as well as the n-alkyl thiols can affect the type of the phase. A number of structures, smectic, undulated smectic and columnar phases, were obtained thanks to the self-segregation of mesogenic and simple n-alkyl ligands at the nanoparticle surface.

New ferroelectric and antiferroelectric liquid crystalline materials containing differing numbers of lactate units

A new series of chiral liquid crystalline materials having the same rigid core containing a keto group, and various numbers of (S)-lactate groups in the chiral segment, has been synthesized and studied. All the compounds contain a branched terminal alkyl chain derived from (S)-2-methylbutanol. The influence of the number of lactate units on mesogenic behaviour has been studied. All the compounds show the paraelectric SmA phase and the ferroelectric SmC* phase over rather wide temperature ranges. The antiferroelectric SmCA* phase was observed for the compound possessing two lactate groups.

Physical gels made of liquid crystalline B4 phase

The achiral liquid crystalline materials showing two B4 (HN) phases have been found to exhibit strong gelation ability for various organic solvents with reversible sol-gel phase transition. The gel is formed by helical tubules, which build entangled 3D network, encapsulating the solvent. The equilibrium of left- and right-handed tubules is preserved in the gel, even if the chiral solvent is used.

Novel hockey‐stick mesogens with the nematic, synclinic and anticlinic smectic C phase sequence

New hockey‐stick mesogens have been synthesised and their mesomorphic properties studied. The molecular structure consists of a laterally substituted central naphthalene unit prolonged by two non‐symmetrical arms, both of which contain ester units of identical orientation. The shorter arm possesses only one and the longer arm three benzene rings. Nematic, synclinic smectic C and anticlinic smectic C phases were identified and their physical properties studied. No banana‐type ordering producing dipolar phases has been found.

Photoconductive Liquid-Crystalline Derivatives of 6-Oxoverdazyl

1,3,5-Triphenyl-6-oxoverdazyl radicals 1[n], in which each phenyl group is substituted with three alkylsulfanyl groups (n = 6, 8, 10), exhibit a monotropic columnar rectangular (Col(r)) phase below 60 °C. Detailed analysis of 1[n] revealed a broad absorption band in the visible region with maxima at 540 and 610 nm and redox potentials E(1/2)(0/+1) = +0.99 V and E(1/2)(0/-1) = -0.45 V vs SCE. Photovoltaic studies of 1[8] demonstrated a hole mobility of 1.52 × 10⁻³ cm² V⁻¹ s⁻¹ in the mesophase with an activation energy of 0.06 ± 0.01 eV. Magnetization studies of 1[8] revealed nearly ideal paramagnetic behavior in either the solid or fluid phase above 200 K and weak antiferromagnetic interactions at low temperatures.

End functionalised liquid crystalline bent-core molecules and first DAB derived dendrimers with banana shaped mesogenic units

New series of non-symmetric bent-core compounds with a terminal carboxylic function as well as its benzyl esters and pentafluorophenyl esters have been synthesised. For most pentafluorophenylesters and for a benzylester with fluorine atoms in the ortho positions to the alkoxy chain different types of columnar ribbon phases (ColrPA and ColobPA) and a polar smectic SmCPA phase have been observed. Both the columnar and the smectic phases show antiferroelectric switching behaviour. Based on these functionalised banana-shaped molecules the first example of an amphiphilic bent-core molecule with a terminal 1-acylaminopropane-2,3-diol unit and DAB derived dendrimers of the first as well as the second generation have been synthesised and their physical properties have been investigated. Neither the diol-terminated bent-core molecule nor the dendrimers show any electrooptical response. Dendrimers with long aliphatic chains as well as the amphiphile form non-polar bilayer smectic phases, whereas dendrimers with shorter chains organise into a mesophase with a 2D lattice (Col). It seems that hydrogen bonding at the periphery of the bent-core units is unfavourable for the formation of polar smectic phases.