Jozef Mieczkowski

Liquid-crystalline phases made of gold nanoparticles.

Spontaneous formation of smectic and columnar structures was observed when spherical gold nanoparticles were functionalized with mesogenic thiols (see layered structure and X-ray pattern of a sample in smectic phase). The particle ordering is stimulated by softening of the interparticle potential and flexibility for deformation of the grafting layer.

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.

Nematic phase formed by banana-shaped molecules

Most mesogens formed by banana-shaped molecules exhibit liquid-like smectic phases. Here we present the synthesis and properties of homologous series of derivatives of resorcinol and 2,6-disubstituted pyridine. One of these classes of bent-core molecules displays the nematic phase.

Dynamically self-assembled silver nanoparticles as a thermally tunable metamaterial

The availability of metamaterials with properties that can be actively tuned is crucial for the future development of various metamaterial-based technologies. Here we show that by using silver nanoparticles equipped with a thermally responsive organic coating a metamaterial is obtained with reversibly switchable properties. The material investigated exhibits dynamic self-assembly resulting from temperature-dependent changes of organic coating shape, which translates to a switchable spatial distribution of the silver nanoparticles. This in turn strongly influences the optical properties of the entire material. The measured optical characteristics of the material are in excellent agreement with theoretical calculations, which allow us to use the latter to predict a dynamically tunable epsilon-near-zero behaviour of the metamaterial. The suggested methodology opens new routes for tunable metamaterials that operate in the visible region and will enable various applications for soft-matter-based optical devices.

Gold nanoparticles solid contact for ion-selective electrodes of highly stable potential readings

Internal solution free ion-selective electrodes were prepared applying for the first time gold nanoparticles as a solid contact layer. The presence of a layer of gold nanoparticles stabilized with aliphatic thiols at the back side of the membrane resulted in highly stable potentiometric responses of the sensors, good selectivities and close to Nernstian slopes. Electrochemical studies have confirmed that the applied material is effectively working as capacitive solid contact, yielding high stability sensors.

Liquid crystalline amorphous blue phase and its large electrooptical Kerr effect

An amorphous blue phase III with low and wide thermal range (∼20 °C) including room temperature is induced by doping a bent-core nematic with a strong chiral material. We confirm that the electrooptical response is due to the Kerr effect, with the Kerr constant being up to two orders of magnitude larger than conventional Kerr materials such as nitrobenzene.

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.

Electrosynthesis and spectroelectrochemical characterization of poly(3,4-dimethoxy-thiophene), poly(3,4-dipropyloxythiophene) and poly(3,4-dioctyloxythiophene) films

Abstract Poly(3,4-dialkoxythiophene) films with different length of alkyl chain (1,3 and 8 carbon atoms) were obtained on Pt and ITO electrodes from the monomer solutions in acetonitrile by cyclic voltammetry (CV). The properties of the resulting films were studied by electrochemical methods, UV–Vis, FTIR and NMR spectra. The CVs were correlated with differential cyclic voltabsorptograms (DCVA) recorded at the absorption maxima to explain the shape of the voltammograms of the polymers studied, dependent on the alkyl-chain length in alkoxy group. The presence of the zones of different crystallinity in the polymer film was postulated. Significant influence of the type of the solvent on asymmetry of the cyclic voltammograms for the polymer doping–undoping has been discussed in terms of the solvent interaction with radical cation (polaron) delocalized on the alkoxy side groups. The polaron delocalization was proved by 1H-NMR spectra. Appearance of infrared activated vibrations (IRAVs) in the range 1500–600 cm−1 and a characteristic electronic band at 3300 cm−1 at the polarization potential +0.25 V versus Ag/Ag+ and their gradual changes upon further polymer oxidation were interpreted in terms of evolution of different charge carriers in lightly and heavily doped polymer.

Bent-core molecules with lateral halogen atoms forming tilted, synclinic and anticlinic, lamellar phases

Four homologous series of symmetric bent-core molecules containing lateral fluorine or iodine substituents in the branches were synthesised and studied. Depending on the central ring and the lateral substituent the studied compounds exhibit a B7 phase or B2 type phases with anticlinic (SmCAPA) or synclinic (SmCSPA) interlayer structures. For the SmCSPA phase the C2v symmetry structure is proposed, with regularly spaced anticlinic–ferroelectric interlayer boundaries. In the SmCAPA phase strong optical activity was detected, chiral domain segregation could be induced by applying a weak electric field.

Liquid crystal phases formed by asymmetric bent-shaped molecules

A few series of asymmetric bent-core compounds with different branches were obtained. Depending on the flexibility and the parity of the unit that joins the central ring with the branches the typical rod-like or banana phases are observed. It is shown that asymmetric materials usually have a broader mesophase range than their symmetric analogues. The rich variety of lamellar and broken-layer columnar phases were found for asymmetric compounds, some of the phases being ferroelectric. Biaxial and uniaxial ferroelectric phases were observed. It has also been proven that some mesophases showing optical bistability under electric fields are unambiguously antiferroelectric.