Liquid crystalline materials forming columnar mesophases are of importance for both the fundamental research and technological applications due to their supramolecular architecture allowing for one-dimensional charge transport. The potential applications of these materials include light emitting diodes, solar cells, field effect transistors and photovoltaic cells. However, to design a LC material suitable for a particular application, a fundamental understanding of the structure-property relationships is needed.<p>In the present thesis, a variety of systems forming columnar mesophases have been explored. They include small molecular weight compounds (triphenylene, phthalocyanine derivatives and star-shaped mesogens) and polymer materials. The research was focused on the study of the influence of the molecular architecture and specific interactions such as hydrogen bonding on the supramolecular organization in the mesophase, as well as on the influence of columnar mesophase on crystal growth. The main results of the thesis are summarized below.<p>The influence of hydrogen bonding on the structure and charge carrier mobility was investigated for a triphenylene derivative, hexaazatriphenylene, having lateral alkyl chains linked to the core via amide groups. These linking groups provide the possibility to form inter- and intra-molecular hydrogen bonds. Acting as “clamps”, the inter-molecular hydrogen bonds are found to enforce the attractive interactions between the molecules in the column. Thus, the columnar mesophase formed by this system is characterized by the smallest inter-disk distance ever found in columnar mesophases (3.18 Å). The improved intra-columnar order brings about a higher charge carrier mobility (0.02 cm2/Vs) as compared to other triphenylene derivatives without hydrogen bonds. <p>Phthalocyanine derivatives, which are liquid crystalline at ambient temperature, could be suitable for opto-electronic applications due to their improved processibility and self-healing of structural defects. Our interest in these systems was inspired by the fact that, in spite of numerous studies performed to date, only very a few phthalocyanine derivatives were found to exhibit columnar mesophases at ambient temperature. We observed that by introducing branches in alkyl chains close to the core, we were able to render the material LC at ambient temperature. Analysis of X-ray diffraction patterns measured on oriented samples showed that these systems form hexagonal and rectangular ordered columnar mesophases. This finding is in contradiction with the general view stating that non-hexagonal mesophases can be only disordered. Since the absolute majority of applications require fabrication of films, it was very important to achieve the visualization of the organization of the phthalocyanine derivatives at the nanometer scale. AFM images on thick spin-coated films with columnar resolution are presented for the first time. They allowed the examination of columnar curvatures and breaks at the boundaries between different single crystal-like domains. <p>The possibility of templating columnar crystal growth was studied for a star-shaped mesogen using a combination of direct- and reciprocal-space techniques. AFM images with columnar resolution showed that the crystal growth initiated in the monotropic columnar mesophase occurs almost in register with the mesomorphic template. In the final crystalline structure, the placement of the crystalline columns is controlled by the mesomorphic tracks at the scale of an individual column, i.e. at the scale of approximately 3.5 nm. <p>The mesophase-assisted crystallization was also studied for the case of a polymer material forming columnar mesophase, poly(di-n-propylsiloxane). X-ray diffraction on oriented fibers allowed us to correct the previous indexation and solve the structure of the unit cell. The crystallization process was studied on samples crystallized in different conditions. It was found that, depending on crystallization conditions, both folded-chain and extended-chain crystals can be obtained. Thus, crystallization of the material from the mesophase results in the formation of 100-150nm thick crystals, which corresponds to a nearly extended-chain conformation. By contrast, when crystallized from a dilute solution, folded-chain crystals result. The mechanisms of chain unfolding was studied by variable temperature atomic force microscopy on PDPS single crystals. It was found that crystals rapidly thicken above the initial melting point, up to 80 nm. / Doctorat en sciences, Spécialisation physique / info:eu-repo/semantics/nonPublished

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Baigiamajame magistro darbe ištirta skystųjų kristalų (cholesterolio stearatas) priedų prie tepimo ir aušinimo skysčio (TAS) įtaka kietlydynio peilio nudilimui ir apdirbto paviršiaus šiurkštumui tekinimo operacijoje. Ištirtas sriegiklio pasipriešinimo momento kitimas sriegiant skyles rankiniais sriegikliais, kai sriegikliai tepami skystaisiais kristalais ir konsistentiniu tepalu. Paviršiaus šiurkštumo tyrimai buvo atlikti tekinant 45 plieninį strypą: pastūma – 0,1 mm/aps., pjovimo greitis buvo keičiamas nuo 85 iki 267 m/min, o cholesterolio stearato kristalų koncentracija emulsijoje – nuo 0,1 iki 0,5 %. Eksperimentas buvo atliekamas pagal dviejų veiksnių ortogonalinį eksperimento planą. Rezultatai pateikti kaip tekinto paviršiaus šiurkštumo parametro Ra priklausomybė nuo pjovimo greičio ir cholesterolio stearato koncentracijos TAS. Peilio užpakalinio paviršiaus nudilimas buvo nustatomas esant tokiems režimams: pjovimo greitis 160 m/min, pastūma 0,1 mm/sūk., aušinimas – mineralinė emulsija BLASOCUT ir ta pati emulsija su 0,1% cholesterolio stearato. Rezultatai pateikti kaip dilimo priklausomybės nuo įrankio kelio grafikai. Nustatyta, kad skystųjų kristalų priedai pagerina įrankio patvarumą ir sumažina įrankio dilimą. Taip pat nustatyta, kad sriegiklio pasipriešinimo momentas mažėja iki 1,1 karto, tepant jį skystaisiais kristalais, lyginant su tepimu konsistentiniu tepalu. Darbą sudaro keturios dalys: įvadas, literatūros analizė, eksperimentiniai tyrimai, išvados. Darbo... [toliau žr. visą tekstą] / The influence of the liquid crystals (cholesteryl stearate) additives on technological properties of the cutting fluid is investigated in the master‘s thesis. Influence of the presence of the liquid crystals in cutting fluid on wear of the carbide lathe tool and roughness of the turned surface is established. Also changes in the cutting torque of the hand tap in the tapping operation were obtained when tap were lubricated with grease and liquid crystals. Research of the surface roughness was done at the following conditions: tool feedrate – 0.1 mm/rev., cutting speed was varied from 85 to 267 m/min and concentration of the liquid crystals was varied from 0.1 to 0.5%. Experimental research was performed by means of two factors second order orthogonal design. The results presented as graphs of dependence of average roughness of turned surface on cutting speed and concentration of the liquid crystals in the coolant. The wear of carbide tool relief face was established under following conditions: cutting speed 160 m/min, feedrate – 0.1 mm/rev., cutting fluid – mineral coolant BLASOCUT with 0.1% and without liquid crystals additives. The results are presented as graphs of dependence of tool wear on the length of tool path. It is established that liquid crystals additive reduces tool wear and increase tool life. It is also established, that cutting torque of the hand tap reduces about 1.5 times when it is lubricated with liquid crystals, as compared with lubrication with... [to full text]

Widefield surface plasmon resonance (WSPR) microscopy provides high resolution imaging of interfacial interactions. We report the application of the WSPR imaging system in the study of the interaction between keratinocytes and liquid crystals (LC). Imaging of fixed keratinocytes cultured on gold coated surface plasmon substrates functionalized with a thin film of liquid crystals was performed in air using a 1.45NA objective based system. Focal adhesion of the cells adhered to glass and LC were further studied using immunofluorescence staining of the vinculin. The imaging system was also simulated with 2x2 scattering matrix to investigate the optical reflection of the resonant plasmonic wave via the glass/gold/cell and glass/gold/LC/cell layers. WSPR imaging indicated that keratinocytes are less spread and formed distinct topography of cell-liquid crystal couplings when cultured on liquid crystal coated substrates. The simulation indicates that glass/LC shifted the surface plasmon excitation angle to 75.39 degrees as compared to glass/air interface at 44 degrees . The WSPR microcopy reveals that the cells remodelled their topography of adhesion at different interfaces.

This thesis focuses on two problems lying within the field of soft condensed matter: the viscous fingering or Saffman-Taylor instability and nematic liquid crystals in confinement. Whenever a low viscosity fluid displaces a high viscosity fluid in a porous medium, for example water pushing oil out of oil reservoirs, the interface between the two fluids is rendered unstable. Viscous fingers develop, grow and compete until a single finger spans all the way from inlet to outlet. Here, using a free energy lattice Boltzmann algorithm, we examine the Saffman-Taylor instability for two different wetting situations: (a) when neither of the two fluids wet the walls of the channel and (b) when the displacing fluids completely wets the walls. We demonstrate that curvature effects in the third dimension, which arise because of the wetting boundary conditions, can lead to a novel suppression of the instability. Recent experiments in microchannels using colloid-polymer mixtures support our findings. In the second part of the thesis we examine nematic liquid crystals confined in wedge-structured geometries. In these systems the final stable configuration of the liquid crystal system is controlled by the complex interplay between confinement, elasticity and surface anchoring. Varying the wedge opening angle this competition leads to a splay to bend transition mediated by a defect in the bulk of the wedge. Using a hybrid lattice Boltzmann algorithm we study the splay-bend transition and compare to recent experiments on {em fd} virus particles in microchannels. Our numerical results, in quantitative agreement with the experiments, enable us to predict the position of the defect as a function of opening angle, and elucidate its role in the change of director structure. This has relevance to novel energy saving, liquid crystal devices which rely on defect motion and pinning to create bistable director configurations.

Liquid crystals are widely used in electronics, medicine and other fields. Analytical separations are important in the development of new liquid crystals to control the purity of synthesized substances. The sample analysis is important for detection of impurities formed during synthesis and for determination of chiral purity of the substance. Liquid crystal-forming substances cannot be separated by capillary zone electrophoresis due to the absence of readily ionizable groups. Electrokinetic chromatography is a method in which a suitable surfactant is added to the background electrolyte. The uncharged substances then interact with the electrically charged surfactant to obtain an effective charge. Separation can occur if they interact differently with the added surfactant. Another problem complicating the analysis is the very low solubility of analytes in water. Separations in this work were therefore carried out under non-aqueous conditions in acetonitrile. However, under these conditions a poor repeatability of the migration times of the substances was observed. Therefore, capillaries with differently coated inner walls were used in subsequent measurements. Surface modification should improve the repeatability of migration times. Several types of capillary coating have been tested. Dynamic coating...