<p> </p> <p>Interfaces separating two fluids are incredibly complex physical structures and are common throughout science, technology, and nature. Examples from daily life include the air-water interface separating a water drop that is dripping from a leaky faucet from the surrounding air and the interface of a soap bubble (which actually consists of two interfaces) separating the interior of the bubble from its exterior. Other common examples from nature include interfaces between falling rain drops and the surrounding air, and the mist that one encounters at beaches, waterfalls, and fountains where the spray droplets are separated from the surrounding air by an interface. Interfaces and manipulating them are key to technological applications such as thin film coating flows and diverse processes involving drop-by-drop processing such as ink-jet printing, drop-wise manufacturing, spray coating, DNA microarraying, and chemical separations, e.g. extraction. Aside from the coating flows example, the aforementioned situations are all examples of free surface flows that involve abrupt and catastrophic topological changes of interfaces that include physical processes such as breakup (also called pinch-off) as in drop breakup, rupture as in liquid-film or liquid-sheet rupture, and coalescence as in drop or bubble coalescence (similar phenomena also arise in sintering and/or fusion of ceramic, metallic, and polymer particles). These topological changes entail what are referred to as finite-time hydrodynamic singularities. For example, at the location(s) where a drop breaks, the thickness of the drop locally tends to zero while fluid pressure and velocity diverge (hence the reason for the word singularity). In addition to hydrodynamic singularities, the presence of surface-active agents or surfactants at fluid interfaces in free surface flows is another reason scientists have been attracted to the study of such problems.</p> <p>Adsorption onto and lowering of the surface tension of a fluid interface by surfactants are exploited in applications such as enhanced oil recovery, coating flows, lung surfactants, drop/jet breakup, and film/sheet rupture, with the latter two being among the prime motivators for this PhD thesis. However, surfactant concentration can be nonuniform at the interface because surfactant molecules can be transported along it by convection and diffusion and also due to normal dilatation and tangential stretching of the interface. Thus, aside from simply lowering surface tension, nonuniformity in surfactant concentration causes gradients in surface tension and gives rise to tangential interfacial (Marangoni) stresses. The latter brings about rich physics including tears of wine, interfacial turbulence in mass transfer, and droplet bouncing. In addition to lowering surface tension and the Marangoni effect, surfactants may also induce surface rheological or viscous effects as surfactant molecules deform against each other. The primary goal of this thesis is to advance the understanding of surface rheological effects in situations involving the breakup of surfactant-covered liquid threads (which also includes jets and drops) and liquid sheets. The fundamental understanding developed in this thesis is likely to prove indispensable in and/or assist the development of new technologies where surface rheological effects are central to the processes at hand, e.g. in controlling drop size distributions and avoiding undesirable satellite droplets and/or misting. An initially unexpected but highly rewarding outcome of the research has been the development of techniques for the measurement of surface viscosities, a task that has heretofore proven to be a formidable challenge to experimentalists.</p> <p>In this thesis, surface rheological effects in free surface flows are examined through both analytical and numerical solution of the incompressible Navier-Stokes equations subjected to the traction boundary condition augmented by the Boussinesq-Scriven constitutive equation to account for surface viscous effects. Rigorous and robust numerical algorithms based on the Galerkin finite element (GFEM) method are developed for predictions of surfactant transport, surface rheological effects and hydrodynamics in response to the motion of moving boundaries. The accuracy of computational predictions is verified by demonstrating that computed results accord well with scaling theories.</p>

När priset på naturtillgångar ökar samt att industrier måste ställa om till en mer hållbar verksamhet innebär detta även en omställning för asfaltsindustrin. Ett sätt för att använda mer återvunnet material i asfaltsindustri är att använda bindemedlet från gammal asfaltsmassa (eng.: reclaimed asphalt pavement, RAP). Detta kan dock inte göras utan komplikationer och därför måste bindemedlet föryngras innan för att kompensera för faktorer så som hög styvhet, låg krakning och trötthetsförmåga samt dålig anti-åldring förmåga hos RAPen. I det här projektet har två olika typer av föryngringsmedel använts; ett växtoljebaserat och ett petroleumbaserat mjukbitumen. Detta för att se om det var möjligt att använda förnybart och återvunnet material i bindemedlet men fortfarande uppnå samma prestanda som konventionellt bindemedel. Två blandningar gjordes hjälp av de två olika föryngringsmedlen och RAPen och analyserades parallellt med ett referensmaterial. Analyserna delades upp i två kategorier: reologi och kemi. Analyserna som föll under reologikategorin var mjukpunkt- och penetrationsanalyser, samt analyser med en dynamisk skjuvning reometer (eng.: dynamic shear rheometer, DSR) och en böjbalksreometer (eng.: bending beam rheometer, BBR). Under kemikategorin fanns analysmetoderna tunnskiktskromatografi med flamjoniseringsdetektor (TLC-FID) och Fourier transform infraröd spektroskopi (FTIR). Resultaten påvisar att åldring påverkas mycket av vilket föryngringsmedel som används, vilket blev tydligt när den reologiska förmågan testades. De kemiska analyserna gav stort sett liknade resultat oberoende av bindemedel. Blandningen som innehöll RAP och mjukbitumen visade sig vara mer mottagligt för åldring jämfört med den andra blandningen som innehöll växtolja, trots att den blandningen innehåller längre halt av RAPen. Vidare visar resultaten att blandningar kan prestera likt referensmaterialet när det kommer till reologi. Från den kemiska aspekten, uppvisar alla bindemedelsmaterial liknande egenskaper. Därför kan slutsatsen att RAPen var återvunnen med framgång när växtolja och mjukbitumen användes. / In recent years there has been a lot of focus on reduction of carbon footprint and sustainable development. For the asphalt industries, a way of doing this is to use reclaimed asphalt pavement (RAP) binders. This cannot be done without any complications and therefore, the RAP binder is normally rejuvenated to compensate for its high stiffness, and other poor properties like susceptibility to low temperature cracking and fatigue damage. In this project, two different ways of using RAP binder are investigated: one vegetable oil-based rejuvenator and one soft bitumen. Using the rejuvenator and soft bitumen together with a RAP binder, two different blends were made and compared to a reference bitumen which is commonly used in Sweden. The blends were made in such a way that the penetration values were close to the reference sample. Aging tests were performed by RTFOT and PAV. The testing of the non-aged and aged binder materials was divided into two sections: rheology and chemistry. The rheology testing included softening point, needle penetration, analysis with dynamic shear rheometer (DSR) and bending beam rheometer (BBR) whereas the chemistry testing included thin layer chromatography with flame ionization detector (TLC-FID) and Fourier transform infrared spectroscopy (FTIR). The results indicated that the ageing resistance of the binder materials is affected by the type of rejuvenator used which especially affects the rheological performance. The chemical performance was almost the same in each blend. The blend containing RAP binder and soft bitumen was more susceptible to ageing compared to the other blend containing oil-based rejuvenator even though the blend contained less of the RAP binder. The results also shows that the blends can perform equal to the reference sample for a rheological point of view. From a chemical point of view, the binders, including the reference, have the same properties. Therefore, the RAP binder was successfully recycled using both a bio-oil rejuvenator and soft bitumen.

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