20.500.12556/RUL-102148 Nematske disperzije feroelektričnih mikroploščic Nematic dispersions of ferroelectric microplatelets V magistrskem delu obravnavamo disperzije feroelektricnih plošcic mikrometrskih dimenzij v nematskem tekocem kristalu. Najprej kratko predstavimo osnovne znacilnosti nematskih tekocih kristalov, nematskih koloidov in feroelektrikov. Nato opišemo materiale in eksperimetnalne metode, ki jih uporabljamo pri poskusih, med njimi so glavne polarizacijska mikroskopija, mikromanipulacija z opticno pinceto in video sledenje koloidnih delcev s hitro kamero. Nato predstavimo metode analize meritev in podamo glavne rezultate eksperimentov. Feroelektricne plošcice v nematskem tekocem kristalu v planarni celici razdelimo na elasticne dipole in kvadrupole glede na konfiguracijo okoliškega direktorskega polja. S pomocjo te razvrstitve obravnavamo interakcije med dvema bližnjima feroelektricnima plošcicama v odsotnosti zunanjega elektricnega polja. Iz poskusov v izotropni tekocini zakljucimo, da je elektricni dipolni moment plošcic, ki še niso bile izpostavljene zunanjemu elektricnemu polju, nezaznatno majhen v odsotnosti zunanjega elektricnega polja in so plošcice vecdomenske. Z opazovanjem posamicnih feroelektricnih plošcic v zunanjem elektricnem polju ocenimo velikost in smer njihovega elektricnega dipolnega momenta po preureditvi domen. Analiziramo tudi interakcije med dvema bližnjima feroelektricnima plošcicama v zunanjem elektricnem polju. S tem potrdimo, da se plošcice efektivno obnašajo kot inducirani elektricni dipoli, v odsotnosti zunanjega elektricnega polja je njihov elektricni dipolni moment zanemarljivo majhen. Rezultati magistrskega dela podajajo novo razumevanje dogajanja v disperzijah feroelektricnih plošcic v nematskih tekocih kristalih, s pomocjo katerega bi lahko dosegli izboljšave v njihovi uporabi. In this thesis we experimentally study dispersions of ferroelectric microplatelets in nematic liquid crystal. Firstly we introduce basic properties of nematic liquid crystals, nematic colloids and ferroelectrics. Then we describe the materials and methods used for experimental work: polarizing microscopy, atomic force microscope, micromanipulation of particles using optical tweezer and video tracking of colloidal particles. Further on, main results of our experiments are presented. Ferroelectric platelets in nematic liquid crystal planar cell are divided into two categories based on the polarizing microscopy images of the surrounding nematic director configuration: elastic dipoles and elastic quadrupoles. This classification is a basis for investigation of interactions between two platelets in close proximity, when external electric field is set to zero. From experiments in the isotropic phase of the liquid crystal we conclude that the electric dipole moment of the platelets which have not yet been exposed to external electric field is insignificant in the absence of external electric field. Platelets most probably contain many ferroelectric domains. By investigating individual ferroelectric platelets in external electric field we can estimate the direction and size of their electric dipole moment after the reorientation of domains. We also analyze how two adjacent platelets interact in external electric field and conclude that they effectively act as induced electric dipoles, but their electric dipole moment is insignificant in the absence of external electric field. Results of experimental work of the thesis offer new understanding of nematic dispersions of ferroelectric platelets and could contribute to improvements in their application. nematski tekoči kristali koloidi nematski koloidi feroelektriki topokemijska pretvorba optična pinceta polarizacijska mikroskopija mikroskop na atomsko silo električno polje Brownovo gibanje nematic liquid crystals colloids nematic colloids ferroelectric topochemical transformation optical tweezer polarizing microscopy atomic force microscope electric field Brownian motion true false false Slovenski jezik Angleški jezik Magistrsko delo/naloga 2018-07-21 07:45:06 2018-07-21 07:45:16 2022-08-15 03:40:28 0000-00-00 00:00:00 2018 0 0 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 87446 3225700 139.pdf 139.pdf 1 CF4B61437B18B8835B6D575240D777DD c19b6eda20e20f5550302c7a26785ae94555dc3d9133c77a9264eef547406a38 7af199a9-a1b5-11eb-a523-00155dcfd717 https://repozitorij.uni-lj.si/Dokument.php?lang=slv&id=112443 Fakulteta za matematiko in fiziko 0 0 0