20.500.12556/DKUM-93499 Privlak in zlivanje kapljic vode na mikrostrukturiranih tekočekristalnih površinah magistrsko delo Attraction and coalescence of water droplets on microstructured liquid crystal surfaces Kapljice na poroznih in mikrostrukturiranih površinah impregniranih s tekočimi kristali, zaradi neravnovesja sil vzdolž stične črte okoli sebe tvorijo omočitveni rob, ki vodi do interakcij dolgega dosega. Za milimetrske kapljice, ki med seboj interagirajo, opazimo tri faze zlivanja: privlak, odtok lubrikanta v omočitvenem robu in zlitje. Uporabljamo hitro kamero za preučevanje teh dinamičnih faz na nematskih in izotropnih tekočekristalnih površinah. Pokažemo, da sta privlak in zlitje hitrejši na mikrostrukturiranih površinah (SLIPS) in v tem primeru ni relevantnih razlik v dinamiki na posamezni tekočekristalni fazi. Na poroznih površinah (LCIPS) je privlak med kapljicami veliko počasnejši, predvsem zaradi debelejše plasti lubrikanta in posledično večjega omočitvenega roba. V tem primeru je tudi zlitje počasnejše. Dinamika kapljic na SLIPS v glavnem sledi analogiji klasičnega vzmetnega nihala, kjer ima površinska napetost vlogo vzmeti in viskoznost vlogo koeficienta dušenja. Takšna analiza je bila nedavno izvedena na podobnih mikrostrukturiranih površinah, impregniranih s silikonskimi olji. V naših eksperimentih v glavnem določimo krajše čase odtoka in ne opazimo nihanja kapljic po prvem vrhu hitrosti. Poleg tega je amplituda drugega vrha hitrosti na LCIPS neodvisna od polmera kapljic, medtem ko je na SLIPS amplituda drugega vrha hitrosti neodvisna od tekočekristalne faze. Končno je nihajni čas v tretji fazi zlitja na SLIPS odvisen od polmera na potenco 3/2, medtem ko na LCIPS tega ne opazimo. Poleg tega nihajni čas ni odvisen od viskoznosti tekočega kristala. To eksperimentalno delo predstavlja izviren pogled na interakcije med kapljicami in njihovo zlivanje na mikrostrukturiranih in poroznih površinah s tekočekristalno prevleko. Droplets on porous and microstructured surfaces lubricated with liquid crystals (LCs) form a wetting ridge due to the imbalance of interfacial forces at the contact line, which leads to a long-range interaction. For millimeter-sized water droplets, three distinct stages are observed within one minute: attraction, drainage of the lubricant in the wetting ridge, and fusion. We use high-speed imaging to study these dynamic stages at nematic and isotropic LC interfaces. We show that droplet attraction and final merging are faster on micropatterned substrates (SLIPS) and that in this case there is no relevant difference between the dynamics on both liquid crystal phases. On porous substrates (LCIPS), droplet attraction is much slower, mainly due to a thicker lubricating film and consequently a larger wetting ridge, and coalescence is also slower on the nematic phase in this situation. The dynamics of droplets on SLIPS essentially follows the classical mass-spring model system, in which the effective surface tension of the water droplets and the viscosity of the lubricant play the role of the spring constant and damping coefficient. Such an analysis was recently applied to similarly structured surfaces impregnated with silicone oils. However, in our experiments, we generally determine shorter drainage times, which depend on the droplet radius, and do not observe drop oscillations after the first velocity peak. Moreover, on SLIPS the second velocity peak after droplet megring appears to scale with with droplet radius regardless of the liquid crystal phase while on LCIPS the second veloctiy peak appears to be independent of droplet raidus but varies between liquid crystal phases. Finally, the period of oscillation in the coalescence stage scales with the droplet radius to the power of 3/2 on SLIPS and not on LCIPS. Furthermore, it does not depend on the LC viscosity. This experimental work provides a first insight into the droplet-droplet interaction and the coalescence mechanism on textured LC-impregnated surfaces. mikrofluidika na odprtih površinah tekoči kristali površinska napetost superhidrofobnost spolzke s tekočino impregnirane površine open surface microfluidics liquid crystals surface tension superhydrophobicity slippery liquid-infused porous surfaces true true false [F. Ferš] Slovenski jezik Angleški jezik Magistrsko delo/naloga 2025-06-29 21:16:04 2025-09-01 13:10:00 2025-09-02 03:22:06 0000-00-00 00:00:00 2025 0 Maribor 0 Maribor 87 str. 0000-00-00 NiDoloceno NiDoloceno NiDoloceno 0000-00-00 0000-00-00 0000-00-00 532.78(043.2) 247222531 MAG_Fers_Filip_2025.pdf MAG_Fers_Filip_2025.pdf 1 267068201411B0B314CEA22F6F41A057 c60a7efa1a147cecc77d6f2da153b82cfc3eb0edeafee19ea90cbc0baab9a826 3038ff2c-6ba9-11f0-bb04-00155d000105 https://dk.um.si/Dokument.php?lang=slv&id=194306 Fakulteta za naravoslovje in matematiko 0 0 0