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Title:Kapljična mikrofluidika za pripravo oljnih in tekočekristalnih emulzij v vodi
Authors:Štanc, Rok (Author)
Tkalec, Uroš (Mentor) More about this mentor... New window
Files:.pdf MAG_Stanc_Rok_2020.pdf (52,58 MB)
MD5: 94A401CD726F69DAE308624ABD124E50
 
Language:Slovenian
Work type:Master's thesis/paper (mb22)
Typology:2.09 - Master's Thesis
Organization:FNM - Faculty of Natural Sciences and Mathematics
Abstract:V magistrskem delu je predstavljeno tvorjenje stabilnih oljnih in tekočekristalnih kapljic v vodi z metodo kapljične mikrofluidike. Delo je sestavljeno iz teoretičnega opisa kapilarnih čipov, režimov tvorjenja kapljic in osnov tekočih kristalov, predstavitve eksperimentalnih metod, uporabljenih materialov, raziskovalne opreme, postopkov izdelave mikrofluidičnih čipov in rezultatov eksperimentov. Preizkusil sem različne načine tvorjenja kapljic s čipom z zbiralno kapilaro in s čipom z injekcijsko in zbiralno kapilaro, pri čemer sem se osredotočil na vplive premerov kapilar, viskoznosti in dinamike tokov uporabljenih kapljevin na velikost nastalih kapljic. Izpopolnil sem se v izdelavi različnih geometrij kapilarnih čipov, pripravi mikroemulzij s površinsko aktivnimi snovmi in analizi optičnih posnetkov dobljenih kapljic. Primerjal sem tudi učinkovitost dveh naprav za poganjanje in kontrolo tokov tekočin v mikrofluidičnem okolju ter izpostavil nekaj prednosti piezokontrolerja tlaka v primerjavi s tlačno črpalko. Ugotovil sem, da čip z injekcijsko in zbiralno kapilaro omogoča najbolj predvidljivo in zanesljivo tvorjenje obstojnih kapljic iz različno viskoznih silikonskih olj v vodi, saj sem z njim uspel tvoriti kapljice s premeri od 20 do 250 mikrometrov in s frekvenco nastajanja med 30 in 3500 herci. Režim kapljanja oziroma curljanja sem okarakteriziral z brezdimenzijskimi števili, dimenzijami odprtin kapilar, viskoznostjo in razmerjem pretokov uporabljenih kapljevin. Pokazal sem, da je monodisperznost kapljic močno odvisna od premera injekcijske kapilare in je najvišja v režimu kapljanja, medtem ko režim curljanja omogoča bistveno hitrejše tvorjenje manjših, a bolj polidisperznih kapljic. V zadnjem sklopu raziskav sem se posvetil kontroliranemu sproščanju vodnih mikrokapljic z barvilom iz večjih tekočekristalnih kapljic. To sem dosegel z lokalnim segrevanjem kapljic z optično pinceto čez temperaturo prehoda nematskega tekočega kristala v izotropno fazo in z dodajanjem različnih koncentracij kationskega surfaktanta v okoliški vodni medij. Ugotovil sem, da ustrezna toplotna oziroma kemična stimulacija napolnjenih kapljic tekočega kristala omogoča kontrolirano in pospešeno sproščanje enkapsulirane vsebine v okolico. Predstavljena dognanja so zanimiva za uporabo v farmaciji in v raziskavah na področju fizike mehke snovi ter za nadaljnji razvoj metod kapljične mikrofluidike z oljem podobnimi materiali.
Keywords:mikrofluidika, kapljice, optična mikroskopija, tekoči kristali.
Year of publishing:2020
Publisher:[R. Štanc]
Source:Maribor
UDC:53:544.252.22(043.2)
COBISS_ID:22868995 New window
NUK URN:URN:SI:UM:DK:ALSVZPT4
Views:273
Downloads:58
Metadata:XML RDF-CHPDL DC-XML DC-RDF
Categories:FNM
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Licences

License:CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International
Link:http://creativecommons.org/licenses/by-nc-nd/4.0/
Description:The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.
Licensing start date:08.06.2020

Secondary language

Language:English
Title:Droplet microfluidics for the production of oil and liquid crystal emulsions in water
Abstract:The master's thesis presents the formation of stable oil and liquid crystal droplets in water, obtained by droplet microfluidics. The work consists of a theoretical description of capillary microfluidic chips, droplet formation, and basics of liquid crystals, followed by a presentation of experimental methods, materials, research equipment, chip fabrication and experimental results. I tested different formations of droplets with two capillary chip geometries, by focusing on the effects of capillary diameters, viscosity, and flow dynamics of applied liquids that greatly influence the size of the resulting droplets. I developed my skills in microfluidic chip fabrication, preparation of microemulsions, and analysis of optical micrographs. I also discussed the efficiency of two devices for driving and controlling the fluid flows in a microfluidic environment and highlighted some advantages of a piezoelectric pressure controller in comparison with syringe pumps. I found that the chip with injection and collection capillary allows the most predictable and reliable formation of silicone oil droplets in water, as I was able to form droplets with diameters from 20 to 250 micrometers and with a frequency between 30 and 3500 hertz. I characterized the dripping and the jetting regime with dimensionless numbers, dimensions of capillary openings, viscosity and flow ratio of used liquids. I have shown that the monodispersity of droplets strongly depends on the diameter of the injection capillary and that it is highest in the dripping regime, while the jetting regime allows for significantly faster formation of smaller but more polydisperse droplets. In the last set of experiments, I focused on the controlled release of aqueous microdroplets with a dye from larger liquid crystal droplets. I achieved this by locally heating the liquid crystal droplets with optical tweezers over the nematic-to-isotropic transition temperature, and by adding different concentrations of cationic surfactant to the surrounding aqueous medium. I found that appropriate thermal or chemical stimulation of filled liquid crystal droplets enables controlled and accelerated release of encapsulated contents into the environment. The presented findings are of interest for use in pharmacy and soft matter physics, as well as for further development of methods of droplet microfluidics with oil-like materials.
Keywords:microfluidics, droplets, optical microscopy, liquid crystals.


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