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

Synthesis and physicochemical properties of liquid crystals, containing steroidal, azobenzene, N-benzylideneaniline and biphenyl moieties, and their application for surface modification of gold and silver nanoparticles

W niniejszej pracy opisane zostały wyniki badań dotyczące syntezy oraz badań strukturalnych i właściwości fizykochemicznych związków ciekłokrystalicznych oraz hybrydowych nanocząstek złota i srebra. Przebadane zostały cztery nowe serie dimerów mezogenicznych, które oprócz typowych faz ciekłokrystalicznych (występowanie faz nematycznych i smektycznych) charakteryzowały się również pewnymi niewystępującymi powszechnie cechami. Serie symetrycznych dimerów, zbudowanych z jednostek bifenylowych oraz azobenzenowych, wykazały ciekłokrystaliczną fazę B4, która wcześniej obserwowana była głównie dla ciekłych kryształów o kształcie bananowym. Faza ta wykazuje zdolność tworzenia żeli fizycznych dla różnych rozpuszczalników organicznych. Zbudowana jest z chiralnych nanofilamentów o kształcie „tubuli” lub „skręconych wstążek”. Seria niesymetrycznych dimerów, zbudowanych z chiralnej jednostki cholesterolowej oraz ugrupowania N-benzylidenoanilinowego, wykazała przejście pomiędzy fazą nematyka chiralnego, a fazą nematyka twist-bend. Otrzymanie związku wykazującego fazę nematyczną twist-bend stabilną w temperaturze pokojowej pozwoliło na przeprowadzenie badań metodą mikroskopii sił atomowych (AFM). Przeprowadzone badania dowiodły, że fazy Ntb tworzone zarówno przez molekuły chiralne, jak i achiralne, są fazami identycznymi termodynamicznie, tak jak fazy nematyczna (N) i cholesteryczna (N*). Seria homologiczna niesymetrycznych, foto-aktywnych dimerów mezogenicznych, zbudowanych z chiralnej jednostki cholesterolowej oraz jednostki azobenzenowej, wykazała fazę nematyczną chiralną (N*), fazę nematyczną typu twist-bend oraz fazę smektyczną A. Dla sześciu materiałów z tej serii uzyskane zostały struktury krystaliczne rzucające nowe światło na możliwe konformacje molekularne oraz rozmieszczenie cząsteczek w fazie ciekłokrystalicznej. Wykazano, że oprócz modelu struktury interkalowanej należy również zwrócić uwagę na model molekuł o silnie wygiętym kształcie. W ramach przeprowadzonych badań otrzymano również ciekłokrystaliczne nanocząstki hybrydowe zbudowane z metalicznego rdzenia (złoto oraz srebro) i przyłączonych kowalencyjnie molekuł ciekłokrystalicznych z foto-aktywnymi ugrupowaniami azowymi. Dla otrzymanych materiałów możliwe są zmiany w strukturze ciekłokrystalicznej zachodzące pod wpływem światła. Okazało się, że pochodne azowe przyłączone do powierzchni nanocząstek wykazują różną kinetykę izomeryzacji trans-cis w porównaniu z wolnymi ligandami. Konformacja cis wolnych ligandów w roztworze jest stabilna przez wiele godzin, podczas gdy izomeryzacja formy cis do formy trans dla molekuł przyłączonych do powierzchni nanocząstek zachodzi w kilka minut. Ze względu na zatłoczone środowisko, ligandy azowe przyłączone do powierzchni metalu zachowują się tak, jakby znajdowały się w fazie skondensowanej.The aim of the thesis was organic synthesis and structural studies in the area of self assembly of liquid crystalline materials. During the research four homologous series of mesogenic dimeric compounds have been synthesized: The first group of compounds is series of symmetric mesogenic dimers made of 4-decyloxy-4’-hydroxybiphenyl units connected by flexible alkyl spacers with an odd number of carbon atoms. These materials are thermotropic liquid crystals, exhibiting two B4-type phases and 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. Second group of mesogenic compounds contains photoactive azobenzene units in molecular structure. This series of dimeric compounds also forming a helical nanofilament phase (B4). We have shown that filaments can be aligned in the macro-scale when grown from aligned smectic phase. Due to the photosensitivity of the mesogenic material, the patterning of the sample is possible by selective UV irradiation, which reversibly melts the B4 phase and as a result locally changes the alignment of nanofilaments. Next groups of mesogenic dimers contains chiral cholesterol unit in molecular structure. Investigated compounds exhibit three types of molecular arrangement in the liquid crystalline phase: chiral nematic (N*), twist-bend nematic (Ntb), and smectic A phase (SmA). The occurrence of orthogonal liquid crystalline SmA phase for the studied compounds is quite unique due to bent shape of their molecules. For most of the currently known compounds exhibiting Ntb phase and smectic phases, the lamellar phases are tilted. The single crystal experiments of the studied materials allowed for a thorough analysis of the structure and arrangement of the molecules in the liquid crystalline phase. It has shown that, in addition to the model of intercalated molecules, special attention should be paid to the model of strongly bent molecules. To the best of our knowledge this model of molecular conformation for flexible linked mesogens has never been considered. The studies presented here show that insightful crystal structure analysis allows future design of liquid crystal materials with the strictly required properties. During research hybrid materials consist of gold and silver nano particles covalently bonded with mesogenic molecules containing azo benzene moieties have been also synthesized. I have obtained phototunable liquid crystalline structures made of metallic clusters (gold and silver) coated with photosensitive azo molecules. These nanoparticles are the first reported to form either a lamellar or a columnar phase that can be reversibly melted by UV light. In the case of particles with a low density of photosensitive ligands in the organic corona, dynamic control of layer spacing was observed as a result of light-induced conformational changes of the azo ligands in the organic sublayer. The kinetics of the transition is fast, and the restoration of the original structure does not require irradiation with visible light. These results suggest the design of new LC plasmonic materials with light-controlled optical properties. Such photodriven switching between LC phases could lead to the control of plasmonic properties in future metamaterials, since it offers a feasible way of changing the nearest-neighbor distance between the metallic cores of nanoparticles

The Impact of Short-Term Shark Liver Oil Supplementation on the Fatty Acid Composition of Erythrocyte Membranes

Fatty acid (FA) balance is strictly related to human health. The composition of fatty acids in lipid membranes seems to be influenced by diet. Shark liver oil (SLO) supplementation has been widely used recently in the prevention and treatment of human diseases. We analyzed the impact of short-term SLO supplementation on certain biochemical parameters and erythrocyte FA composition in a group of young healthy women. Our results showed that 6 weeks of SLO supplementation led to a significant decrease in C-reactive protein levels in sera and intracellular cholesterol levels in peripheral blood mononuclear cells. SLO supplementation caused a significant increase in the content of the polyunsaturated omega-3 FAs: docosahexaenoic acid, docosapentaenoic acid and α-linolenic acid. In the group of omega-6 FAs, we observed a significant elevation of arachidonic and dihomo-gamma-linoleic acid content. Due to these alterations, the omega-3 index increased significantly from 3.6% (before) to 4.2% (after supplementation). We also observed the impact of SLO supplementation on the membrane fluidity index. The ratio between saturated and unsaturated FAs decreased significantly from 13.1 to 9.9. In conclusion, our results show that even short-term SLO supplementation can improve human erythrocyte fatty acid composition and other parameters that may have health-promoting consequences

Eu3+ and Tb3+ doped LaPO4 nanorods, modified with a luminescent organic compound, exhibiting tunable multicolour emission

Co-precipitation reaction followed by hydrothermal treatment were used to synthesise Eu3+ or Tb3+ doped LaPO4 nanorods, of 5–10 nm in width and 50–100 nm in length. Surface modification of the as-prepared nanoparticles with a selected luminescent organic compound resulted in formation of hybrid inorganic–organic nanomaterials. The products obtained exhibited tunable multicolour luminescence, dependent on the surface modification and applied excitation wavelength. The colour of their emission can be altered from red- orange to yellow-green. Powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) confirmed the structure and morphology of the products synthesized. Successful surface modification of the nanophosphors was evidenced by analytical and spectroscopic techniques such as dynamic light scattering (DLS) – providing size distribution histograms and zeta potentials of the nanoparticles; IR spectroscopy and elemental analysis which proved the presence of an organic phase in the structure; spectrofluorometry (excitation/emission spectra and luminescence decay curves) which confirmed the formation of hybrid, surface modified nanomaterials revealing tunable multicolour emission

Eu3+ and Tb3+ doped LaPO4 nanorods, modified with a luminescent organic compound, exhibiting tunable multicolour emission

Co-precipitation reaction followed by hydrothermal treatment were used to synthesise Eu3+ or Tb3+ doped LaPO4 nanorods, of 5–10 nm in width and 50–100 nm in length. Surface modification of the as-prepared nanoparticles with a selected luminescent organic compound resulted in formation of hybrid inorganic–organic nanomaterials. The products obtained exhibited tunable multicolour luminescence, dependent on the surface modification and applied excitation wavelength. The colour of their emission can be altered from red- orange to yellow-green. Powder X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) confirmed the structure and morphology of the products synthesized. Successful surface modification of the nanophosphors was evidenced by analytical and spectroscopic techniques such as dynamic light scattering (DLS) – providing size distribution histograms and zeta potentials of the nanoparticles; IR spectroscopy and elemental analysis which proved the presence of an organic phase in the structure; spectrofluorometry (excitation/emission spectra and luminescence decay curves) which confirmed the formation of hybrid, surface modified nanomaterials revealing tunable multicolour emission

Linkage-length dependent structuring behaviour of bent-core molecules in helical nanostructures

We studied the correlation between the molecular structure and the formation of helical nanofilaments (HNFs) of bent-core dimeric molecules with varying linkage lengths. To obtain precise structural data, a single domain of HNFs was prepared under physical confinement using porous 1D nanochannels, made up of anodic aluminium oxide films. Electron microscopy and grazing incidence X-ray diffraction were used to elucidate the linkage length-dependent formation of HNFs.clos