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V zaključni nalogi smo obravnavali problem ovrednotenja interakcije superhidrofilne površine s kapljevitim medijem, saj klasična metoda merjenja kota omočenja statične kapljice, ne omogoča ustreznega ovrednotenja. Uporabili smo metodo ovrednotenja hitrosti kapilarnega vleka, pri kateri merimo hitrost iztekanja kapljevine iz kapilare ob stiku s površino trdne snovi. V ta namen smo razvili merilno progo in z njo izvedli meritve na različno obdelanih vzorcih. Uporabili smo bakrene ploščice in z različnimi vzorci strukturiranja izdelali superhidrofilne površine. Z merilno progo smo beležili časovno odvisnost spremembe višine kapljevine v kapilari, spreminjanje višine pa smo merili s hitro kamero. Meritve smo izvedli s cevko z notranjim premerom 0,5 mm, v kateri je bilo približno 1 µL destilirane vode. Po obdelavi posnetkov meritev smo dobili grafe premika gladine kapljevine v kapilari, iz katerih smo lahko določili hitrost kapilarnega vleka vzorca. Na bakrenih površinah smo naredili križne vzorce z različnimi razmiki med črtami in ugotovili, da so hitrosti kapilarnega vleka največje na vzorcu z najmanjšim razmikom. S povečevanjem razmika med črtami križnega vzorca, se hitrost kapilarnega vleka zmanjšuje. This study evaluates the interaction of the fluid with the superhidrophility surface, as the classic method of measuring the wetting angle of a static droplet does not allow an adequate evaluation. The method based on the measurement of wicking velocity was applied for this purpose. This approach was used to measure the speed of the liquid when flowing out of the capillary tube that was in contact with the surface. The necessary experimental setup used to perform measurements on various samples has been developed. As superhidrophilic surfaces the copper plates with different patterns made by laser modification were used. The time dependence of the liquid height in the capillary was measured with high-speed camera. The measurements have been done with a tube that contained approximately 1 μL of distilled water. The inner diameter of tube was 0,5 mm. By analysing images taken with the high-speed camera the wicking velocity of the samples modified by laser was determined. It was detected that the wicking velocity is the highest on the sample with the smallest spacing. By increasing the spacing between the lines of the cross pattern the wicking velocity decreases.

Površine s specifično omočljivostjo so uporabne na različnih področjih tehnike, v kmetijstvu, živilski industriji in medicini. V naravi omočljivost ali neomočljivost površin živali in rastline izrabljajo za preživetje. Najbolj poznan je primer superneomočljive površine lotosovega lista, ki se odraža tudi v samočistilnosti, ki preprečuje razrast bakterij in mikroorganizmov. V zaključni nalogi pokažemo, da je superneomočljive kovinske površine mogoče izdelati s kombinacijo laserskega teksturiranja kovinskih površin in njihovega naknadnega nizkotemperaturnega žarjenja v kontaminirani peči. Vzorce iz nerjavnega jekla smo lasersko teksturirali s pomočjo vlakenskega laserja z 28 ns bliski ter valovno dolžino 1060 nm. Zatem smo jih nizkotemperaturno žarili pri 100°C, 200°C, 250°C in 300°C. Pred, med in po žarjenju smo na vzorcih spremljali kot omočenja in kot skotaljenja vodne kapljice. Žarjenje smo ponovili v dveh pečeh pri enakih temperaturah z namenom identifikacije vpliva okoliške atmosfere na prehod iz omočljivega v neomočljivo stanje vzorcev. Ugotovili smo, da do prehoda iz omočljivega v neomočljivo stanje pride zaradi adsorpcije organskih kontaminantov, ki so bili prisotni v peči. Surfaces with unique wettability are used in various fields of technology, in agriculture, food industry and medicine. The animals and plants exploit the hydrophilicity or hydrophobicity for their survival. The most famous example of the superhydrophobic surface in nature is the lotus leaf, which has also the self-cleaning ability and in this way, it prevents the growth of bacteria and microorganisms. In this BSc thesis, we demonstrate that superhydrophobic metal surfaces can be produced by a combination of laser texturing and their subsequent low-temperature annealing in a contaminated furnace. Stainless steel samples were laser textured by using a fibre laser radiating 28-ns pulses with a wavelength of 1060 nm. The laser-processed samples were further annealed at 100 °C, 200 °C, 250 °C and 300 °C. Before, during and after annealing, we measured the contact and the roll-off angle of water droplet. The annealing was repeated in two furnaces at the same temperatures in order to identify the influence of the surrounding atmosphere on the hydrophilic-to-hydrophobic transition of the laser-textured samples. We found that this transition occurs due to the adsorption of organic contaminants that were present in the furnace.

V nalogi obravnavamo vpliv različno strukturiranih površin aluminija na izboljšanje prenosa toplote pri mehurčastem vrenju redestilirane vode v bazenu. Posamezne vzorce smo pripravili z različnimi kombinacijami laserskega strukturiranja in nanosa hidrofobnega premaza. Eksperimentalno smo ovrednotili vrenje na neobdelani površini, hidrofobni površini, dveh hidrofilnih površinah in štirih bifilnih površinah, ki smo jih obdelali z različnimi laserskimi parametri ter na dveh bifilnih površinah, ki nista imeli hidrofobnega premaza. Površine smo testirali na merilni progi za nasičeno vrenje v bazenu pri atmosferskem tlaku. Na merilni progi smo zabeležili vrelne krivulje do nastopa kritične gostote toplotnega toka (CHF) in iz njih izračunali koeficiente toplotne prestopnosti za posamezen vzorec. Pri analizi podatkov smo dobljene rezultate primerjali z referenčno površino (neobdelana aluminijasta površina). Vrednosti CHF so dosegale vrednosti med 890 kW/m2 in 1480 kW/m2. Najvišje vrednosti CHF in koeficienta toplotne prestopnosti so dosegale bifilne površine. Najvišja izmerjena vrednost CHF (1480 kW/m2) je predstavljala 30 % izboljšanje vrednosti CHF referenčne površine, kar pa je pomenilo zvišanje za 320 kW/m2. Zvišanje koeficienta toplotne pristopnosti pa je bilo 83 % in je tako dosegalo vrednosti 61,7 kW/m2K. Dokazali smo, da z lasersko strukturiranimi bifilnimi površinami lahko izboljšamo parametre vrenja v bazenu in s tem bistveno pripomoremo k izboljšanju prenosa toplote. In this work, we investigate the influence of aluminuim surfaces with different structures on enhanced pool boiling heat transfer of twice distilled water. Individual samples were modified by using different combinations of laser texturing and hydrophobization. An untreated surface, a hydrophobic surface, two hydrophilic surfaces and four biphilic surfaces textured with different laser processing parameters as well as two biphilic surfaces without a hydrophobic coating were experimentally tested. Surfaces were tested on saturated pool boiling experimental setup. Boiling curves up to the CHF values were measured and heat transfer coefficient was calculated. In the analysis, the results were compared with the reference surface (raw aluminium surface). CHF values reached values between 890 kW/m2 and 1480 kW/m2. The highest measured values of CHF and heat transfer coefficient were reached by biphilic surfaces (1480 kW/m2) which represent a 30 % improvement regarding to the reference surface. Heat transfer coefficient improvement reached up to 83 % and achieved the highest value at 61,7 kW/m2K. We have demonstrated that laser-structured biphilic surfaces can improve the pool boiling parameters and can significantly contribute to the improvement of boiling heat transfer.

V zaključni nalogi predstavljam rezultate trimesečnega opazovanja sprememb omočitvenih lastnosti različnih lasersko teksturiranih vzorcev nerjavnega jekla AISI 316L. Spremljala sem omočljivost lasersko teksturiranih vzorcev brez nanosov ter z nanosi epoksidne smole in epoksidne smole z nanovključki FAS-TiO2 pri sobnih pogojih ter pri zmanjšanima zračnem tlaku in vlagi. Z meritvami kontaktnih kotov vodnih kapljic sem določila omočitvene lastnosti površin ter njihovo površinsko energijo. Z optično profilometrijo in vrstično elektronsko mikroskopijo sem analizirala hrapavost in morfologijo površin različno obdelanih vzorcev. Rezultati so pokazali, da lahko superhidrofobnost jekla dosežemo posredno s staranjem lasersko teksturirane površine z ustreznimi parametri ali pa neposredno z nanosi epoksidne smole z nanovključki FAS-TiO2. Zračna tlak in vlaga vplivata na spremembe omočljivosti lasersko teksturiranega jekla brez nanosov, na omočitvene lastnosti lasersko teksturiranih vzorcev z nanosi pa nimata vpliva. Pokazala sem, da je laserska obdelava učinkovita metoda za modifikacijo morfologije površin in s tem njihove omočljivosti. This work presents the results of a three-month observation of wetting properties of differently laser-textured stainless steel AISI 316L. The samples were prepared uncoated, coated with epoxy resin, and with epoxy resin composite with inlcusion of FAS-TiO2 nanoparticles. The measurements were performed on samples kept under ambient conditions, and in conditions with reduced air pressure and humidity. Static water contact angles were measured and surface energy was calculated to evaluate surface wetting properties. Optical profilometry and scanning electron microscopy were used to analyze the roughness and morphology of laser-textured steel surfaces. The results have shown that superhydrophobicity of steel can be achieved either indirectly by aging the appropriately laser-textured surface, or directly by application of the epoxy resin composite with FAS-TiO2 nanoparticles. Ambient conditions have a significant impact on changes of wettability of laser-textured steel without coatings, but they do not affect the aging of additioanlly coated surfaces. I have shown that laser processing is an effective method for modifying surface morphology and, consequently, its wettability.