magistrsko delo
Peter Medle Rupnik (Author), Alenka Mertelj (Mentor)

Abstract

Tekoči kristali so dobro poznani po tem, da se dobro odzivajo na zunanje električno polje. Ta odziv je tipično neodvisen od predznaka električnega polja. V suspenzijah magnetnih nanoploščic v tekočekristalnem mediju je po drugi strani mogoče doseči spontano magnetno ureditev, tako da je odziv na magnetno polje linearen. V tem primeru je mogoče z majhnimi magnetnimi polji kontrolirati strukture v materialu, ki ga v našem primeru zapremo v tanko urejeno plast. Z izbiro kiralnega tekočekristalnega medija (holesterični tekoči kristal) pridobimo še bolj zanimiv material. Zvito osnovno stanje holesterika namreč tekmuje s homogenimi zunanjimi polji in robnimi pogoji na mejah tanke plasti. Izkaže se, da je mogoče s kombinacijo zunanjega električnega in magnetnega polja stabilizirati vrsto kompleksnih polarnih struktur. Poleg tega dinamični odziv v tem primeru ni več invarianten na predznak zunanjega električnega polja v primeru, da je vklopljeno tudi zunanje magnetno polje. Slednje je posledica zlomov simetrij zaradi kiralnosti tekočekristalnega medija in spontane magnetizacije. V tem delu je opisanih več značilnosti tega materiala, hkrati pa so predstavljene študije morfologije in dinamike feromagnetnega holesteričnega tekočega kristala zaprtega v tanko urejeno plast.

Keywords

tekoči kristali;feromagnetni tekoči kristali;holesterični tekoči kristali;feromagnetizem;nematodinamika;hidrodinamika;kiralnost;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL FMF - Faculty of Mathematics and Physics
Publisher: [P. Medle Rupnik]
UDC: 538.9
COBISS: 77424387 Link will open in a new window
Views: 225
Downloads: 37
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Other data

Secondary language: English
Secondary title: Suspensions of magnetic nanoplatelets in cholesteric liquid crystals
Secondary abstract: Liquid crystals are well-known for their strong response to the external electric field. This response however is typically independent of the sign of external electric field. Suspensions of magnetic nanoplatelets in liquid crystal media on the other hand exhibit spontaneous magnetic ordering and thus respond linearly to the external magnetic field. Hence moderate magnetic fields can be used to control the structure of the material, which is in our case confined to a thin ordered layer. If the chosen liquid crystal media is chiral (cholesteric liquid crystals), the resulting material is even more interesting. Wound cholesteric ground state competes with homogeneous external aligning fields and boundary conditions on the layer borders. It turns out that many complex polar structures can be stabilised with the combination of external electric and magnetic fields. Additionally, the dynamic is in this case no longer invariant to the sign of electric field, when the external magnetic field is simultaneously applied. This is a consequence of the specific symmetry breakings due to the chirality of cholesteric liquid crystals and spontaneous magnetisation. Here, several features of this material are described and experiments examining the morphology and dynamics are presented.
Secondary keywords: liquid crystals;ferromangetic liquid crystals;cholesteric liqid crystals;ferromagnetism;nematodynamics;hydrodynamics;chirality;
Type (COBISS): Master's thesis/paper
Study programme: 0
Thesis comment: Univ. v Ljubljani, Fak. za matematiko in fiziko, Oddelek za fiziko
Pages: 50 str.
ID: 13495794