Determining the surface tension of a nematic liquid crystal and some isotropic liquids in contact with functionalised glass surfaces by capillary rise

V magistrskem delu so predstavljene meritve močenja in kapilarnega dviga vode, glicerola, silikonskega olja in tekočega kristala na obdelanih steklenih površinah z namenom določitve površinske napetosti. Delo je sestavljeno iz teoretičnega opisa kapilarnih pojavov s poudarkom na računanju oblike meniskusa in višine kapilarnega dviga, predstavitve fizikalnih lastnosti uporabljenih materialov in eksperimentalnih metod ter rezultatov. Razvil sem postopek merjenja kontaktnih kotov kapljevin na ravnih podlagah s prilagojenim optičnim mikroskopom s horizontalno postavitvijo objektivov, ki je bil uporaben tudi za določanje oblike meniskusov in meritve višin kapilarnih dvigov v cilindričnih kapilarah. Ugotovil sem, da ima obdelava steklenih površin s silanom različen vpliv na močenje polarnih in nepolarnih kapljevin, kar se pozna tudi pri spreminjanju višine kapilarnih dvigov. Pokazal sem tudi, da se anizotropne lastnosti nematskega tekočega kristala izrazijo v anizotropiji površinske napetosti, ki je odvisna od robnih pogojev na površini stekla. Metoda kapilarnega dviga v ozkih cilindričnih kapilarah se je izkazala kot enostaven, učinkovit, ponovljiv in dovolj natančen način določanja površinske napetosti različnih vrst kapljevin, ki je uporabna tudi za raziskovanje vpliva kemijske funkcionalizacije površin na lastnosti močenja. The master’s thesis presents measurements of wetting and capillary rise of water, glycerol, silicone oil and nematic liquid crystal on chemically treated glass surfaces with intention of determining the surface tension. The work consists of a theoretical description of the capillary phenomena, presentation of the physical properties of the materials, applied experimental methods and final results. I demonstrated the technique of measuring the contact angles of liquids on flat surfaces with an adjusted optical microscope which was also applied to measure the shape of liquid meniscus and the height of capillary rise in cylindrical capillaries. I have shown that the functionalization of glass surfaces with a silane strongly influences wetting of polar and non-polar liquids, which is also reflected in changing the height of the capillary rise. Further, I demonstrated that the anisotropic properties of a nematic liquid crystal are reflected in anisotropy of the surface tension since it strongly depends on the glass surface boundary conditions. I found that the method of capillary rise provides simple, accurate, comparable and reproducible way of determining the surface tension of various types of liquids. Lastly, it can be also used to investigate wetting properties on chemically functionalized surfaces.