Vpliv nanodelcev na tekočekristalno urejanje

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Language:	Slovenian
Year of publishing:	2012
Source:	Ljubljana
Typology:	2.11 - Undergraduate Thesis
Organization:	UL PEF - Faculty of Education
Publisher:	[M. Trček]
UDC:	532.783(043.2)
COBISS:	9368649
Views:	1038
Downloads:	269
Average score:	0 (0 votes)
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Secondary language:	English
Secondary title:	The impact of nanoparticles on liquid-crystalline order
Secondary abstract:	Liquid crystals are materials that exhibit order between the one of solid crystalline and isotropic liquid phase. The main characteristic of liquid crystals is the molecular anisotropy, because of which a liquid crystal has the ability to exhibit orientational order and in some cases one-dimensional positional disorder. In our research we did not only focus on the properties of liquid crystals, but we also compared the properties of mixtures of liquid crystals and nanoparticles with the properties of the former. Nanoparticles are very small particles, with diameter smaller than 100 nm. For our research we have used nearly spherical nanoparticles, consisting of a 3.5 nm CdSSe core and hydrophobic chains on its surface. We prepared an experiment, where we observed the evolution of the heat capacity with increasing or decreasing temperature for a 5% mixture of liquid crystal and nanoparticles. The analysed experimental data were plotted in graphs in order to determine the number of phase transitions and the temperatures at which they occur. By this method we were able to discern the advantages of liquid crystal compound with nanoparticles with respect to the pure liquid crystal compound. The mixture with nanoparticles has wider temperature ranges of blue phases. Besides that, by adding nanoparticles we induced new liquid crystalline phases. The unique pattern of the calorimetric graph suggests that these are the chiral line liquid phase NL* and the twist-grain boundary TGBA phase. We confirmed the calorimetric results by observing and capturing the textures by the polarized microscopy. At the end we built a model of the liquid crystalline ordering in a newly stabilized TGBA phase. This phase is characterized by the periodic structure of vortex-like defects, locations of disorder. One part of this structure is presented by a mechanical model.
Secondary keywords:	physics;fizika;
File type:	application/pdf
Type (COBISS):	Undergraduate thesis
Thesis comment:	Univ. Ljubljana, Pedagoška fak., Fak. za matematiko in fiziko, Matematika in fizika
Pages:	II, 33 f.
Type (ePrints):	thesis
Title (ePrints):	The impact of nanoparticles on liquid-crystalline order
Keywords (ePrints):	tekoči kristali
Keywords (ePrints, secondary language):	liquid crystals
Abstract (ePrints):	Tekoči kristali so snovi, ki se med trdno kristalno in izotropno kapljevinasto fazo uredijo še v nekatere stabilne vmesne faze, katerim pravimo tekočekristalne faze. Značilnost tekočih kristalov je anizotropnost molekule, zaradi česar lahko kristal v tekočekristalnih fazah vzpostavi orientacijski red in v nekaterih primerih enodimenzionalni pozicijski red. Pri raziskovanju se nismo osredotočili le na lastnosti tekočih kristalov, primerjali smo lastnosti mešanice tekočih kristalov in nanodelcev z lastnostmi čistega tekočega kristala. Nanodelci so zelo majhni delci s premerom do 100 nm. Za našo raziskavo smo uporabili skoraj sferične nanodelce, sestavljene iz 3,5 nm velikega jedra CdSSe in hidrofobnih verig na površini. Pripravili smo eksperiment, pri katerem smo s kalorimetrom opazovali spreminjanje toplotne kapacitete s spreminjanjem temperature za 5-odstotno tekočekristalno mešanico z nanodelci. Analizirali smo meritve in narisali grafe, da bi določili število in temperaturna območja faznih prehodov. Na ta način smo ugotovili, kakšne so prednosti mešanice pred tekočimi kristali brez nanodelcev. Kompozit ima širša temperaturna območja modrih faz. Poleg tega smo z dodajanjem nanodelcev inducirali nove tekočekristalne faze. Značilna oblika grafa iz kalorimetrije nam pove, da gre za tekočo vijačno nematsko fazo NL* in smektično TGBA fazo. Rezultate iz kalorimetrije smo potrdili z mikroskopskimi posnetki tekstur. Na koncu smo izdelali model urejanja tekočega kristala v novo stabilizirani TGBA fazi. Za to fazo je značilna periodična struktura vijačnih defektov, območij nereda. En del take strukture smo predstavili z mehanskim modelom.
Abstract (ePrints, secondary language):	Liquid crystals are materials that exhibit order between the one of solid crystalline and isotropic liquid phase. The main characteristic of liquid crystals is the molecular anisotropy, because of which a liquid crystal has the ability to exhibit orientational order and in some cases one-dimensional positional disorder. In our research we did not only focus on the properties of liquid crystals, but we also compared the properties of mixtures of liquid crystals and nanoparticles with the properties of the former. Nanoparticles are very small particles, with diameter smaller than 100 nm. For our research we have used nearly spherical nanoparticles, consisting of a 3.5 nm CdSSe core and hydrophobic chains on its surface. We prepared an experiment, where we observed the evolution of the heat capacity with increasing or decreasing temperature for a 5% mixture of liquid crystal and nanoparticles. The analysed experimental data were plotted in graphs in order to determine the number of phase transitions and the temperatures at which they occur. By this method we were able to discern the advantages of liquid crystal compound with nanoparticles with respect to the pure liquid crystal compound. The mixture with nanoparticles has wider temperature ranges of blue phases. Besides that, by adding nanoparticles we induced new liquid crystalline phases. The unique pattern of the calorimetric graph suggests that these are the chiral line liquid phase NL* and the twist-grain boundary TGBA phase. We confirmed the calorimetric results by observing and capturing the textures by the polarized microscopy. At the end we built a model of the liquid crystalline ordering in a newly stabilized TGBA phase. This phase is characterized by the periodic structure of vortex-like defects, locations of disorder. One part of this structure is presented by a mechanical model.
Keywords (ePrints, secondary language):	liquid crystals
ID:	8310725