Jarosław Makowiecki

Langmuir-Blodgett films as aligning layers for homeotropic alignment of liquid crystal molecules

In this work, we studied properties of Langmuir and Langmuir-Blodgett molecular films formed by mixture of arachidic acid with nematic liquid crystal mixture having the negative dielectric anisotropy. The Langmuir films were characterised by surface pressure versus mean molecular area isotherms (π–A isotherms) and subsequently were transferred at a particular surface pressure onto hydrophillic and hydrophobic quartz substrates forming monolayer and multilayer Langmuir-Blodgett films. Miscibility of the compounds in the Langmuir films was determined. Absorption spectra of the Langmuir-Blodgett films were recorded in UV-Vis region in order to reveal organisation of the molecules. Morphology of deposited films was visualised using atomic force microscope (AFM) working in tapping mode. Finally, Langmuir-Blodgett films were deposited onto glass plates covered with indium tin oxide (ITO, transparent and conductive electrodes) and were used as aligning layers in laboratory model of Vertical Alignment-type liquid crystal display (LCD). Liquid crystal sandwich cells were filled with nematic mixture doped with a dichroic anthraquinone-dye. On the basis of the light transmission through the liquid crystal cell upon the voltage applied the basic electro-optical parameters such as threshold voltage, driving voltage and contrast were determined.

Miscibility of dl-α-tocopherol β-glucoside in DPPC monolayer at air/water and air/solid interfaces

The role of newly synthesized tocopherol glycosidic derivative in modifying molecular organization and phase transitions of phospholipid monolayer at the air/water interface has been investigated. Two-component Langmuir films of dl-α-tocopheryl β-D-glucopyranoside (BG) mixed with dipalmitoyl phosphatidylcholine (DPPC) in the whole range of mole fractions were formed at the water surface. An analysis of surface pressure versus mean molecular area (π-A) isotherms and Brewster angle microscope images showed that the presence of BG molecules changes the structure and packing of the DPPC monolayer in a BG concentration dependent manner. BG molecules incorporated into DPPC monolayer inhibit its liquid expanded to liquid condensed phase transition proportionally to the BG concentration. The monolayers were also transferred onto solid substrates and visualized using an atomic force microscope. The results obtained indicate almost complete miscibility of BG and DPPC in the monolayers at surface pressures present in the biological cell membrane (30-35·10(-3) N·m(-1)) for a BG mole fraction as high as 0.3. This makes the monolayer less packed and more disordered, leading to an increased permeability. The results support our previous molecular dynamics simulation data.

Characterization of titanyl phthalocyanine (TiOPc) thin films by microscopic and spectroscopic method

The titanyl phthalocyanine (TiOPc) thin film deposited on glass, silicon and gold substrate have been studied using Raman spectroscopy, atomic force microscopy (AFM), absorption and profilometry measurements. The TiOPc thin layers have been deposited at room temperature by the quasi-molecular beam evaporation technique. The Raman spectra have been recorded using micro Raman system equipped with a confocal microscope. Using surface Raman mapping techni que with polarized Raman spectra the polymorphic forms of the TiOPc thin films distribution have been obtained. The AFM height and phase image were examined in order to find surface features and morphology of the thin films. Additionally to compare experimental results, structure optimization and vibrational spectra calculation of single TiOPc molecule were performed using DFT calculations. The received results showed that the parameters like polymorphic form, grain size, roughness of the surface in TiOPc thin films can well characterize the obtained organic thin films structures in terms of their use in optoelectronics and photovoltaics devices.