Privlak in zlivanje kapljic vode na mikrostrukturiranih tekočekristalnih površinah : magistrsko delo

Ferš, Filip

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Title:	Privlak in zlivanje kapljic vode na mikrostrukturiranih tekočekristalnih površinah : magistrsko delo
Authors:	ID Ferš, Filip (Author) ID Tkalec, Uroš (Mentor) More about this mentor...
Files:	MAG_Fers_Filip_2025.pdf (7,19 MB) MD5: 267068201411B0B314CEA22F6F41A057
Language:	Slovenian
Work type:	Master's thesis/paper
Typology:	2.09 - Master's Thesis
Organization:	FNM - Faculty of Natural Sciences and Mathematics
Abstract:	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.
Keywords:	mikrofluidika na odprtih površinah, tekoči kristali, površinska napetost, superhidrofobnost, spolzke s tekočino impregnirane površine
Place of publishing:	Maribor
Place of performance:	Maribor
Publisher:	[F. Ferš]
Year of publishing:	2025
Number of pages:	87 str.
PID:	20.500.12556/DKUM-93499
UDC:	532.78(043.2)
COBISS.SI-ID:	247222531
Publication date in DKUM:	01.09.2025
Views:	156
Downloads:	40
Metadata:
Categories:	FNM
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Licences

License:	CC BY 4.0, Creative Commons Attribution 4.0 International

Link:	http://creativecommons.org/licenses/by/4.0/
Description:	This is the standard Creative Commons license that gives others maximum freedom to do what they want with the work as long as they credit the author.
Licensing start date:	01.09.2025

Secondary language

Language:	English
Title:	Attraction and coalescence of water droplets on microstructured liquid crystal surfaces
Abstract:	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.
Keywords:	open surface microfluidics, liquid crystals, surface tension, superhydrophobicity, slippery liquid-infused porous surfaces

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