Biological degradable polymers on a basis of renewable raw materials, such as polysaccharides, represent promising alternatives to synthetic polymers used as flocculant or stabilizing agents. Polysaccharides derived from potato starch and chitosan have been modified with benzyl- and the first one with additionally cationic hydroxypropyl-trimethylammonium groups of different degrees of substitution (DS). The aim of this work was to characterize the solution properties of these novel amphiphilic polysaccharides concerning the impact of their DS on charge density, particle size, dynamic surface tension and viscosity behaviour. The work is further focused on investigations on flocculation properties of these amphiphilic polyelectrolytes in dispersions of kaolin and silica to identify the interplay between charge density and hydrophobicity. Flocculation efficiency has been evaluated via joint analysis of charge density measurements (using polyelectrolyte titration), turbidity and TOC measurements, as well as dynamic surface tension measurements applying the drop profile analysis. Particle sizes and particle size distributions have been determined by dynamic light scattering and laser diffraction methods. In addition, these amphiphilic starch derivatives have been used to remove substances which impact negatively the paper production process when using recycled paper, so called stickies. Model suspensions have been studied using a multitude of different measurement techniques with the aim to predict a “sticky potential” and to reduce containing dissolved and colloidal substances such as micro stickies. The surface activity and viscometric behaviour have been studied of solely cationic and moderately and highly substituted, amphiphilic polysaccharides in salt-free and 0.05 M NaCl aqueous solution. For the first time dynamic surface tension measurement results have been correlated with particle sizes and apparent charge density. Rheological investigation of large concentration ranges (0.01–20 g/L) was used to discuss Huggins plots and typical polyelectrolyte behaviour for all polysaccharide derivatives could be found. Overlap concentration and, in dilute aqueous solution, intrinsic viscosity could be determined. For polysaccharide solution in dilute regime semi-empirical equations of Rao and Wolf have been applied, making it possible to get insights to polyelectrolyte conformation in dependence on the DS of both substituents. It is shown that for intrinsic viscosity a change of the impact of both substituents takes place when having derivatives with enhanced hydrophobicity. Data evaluation via the ratio of both DS values had been successfully utilized and thus, the applied method has been identified as being a promising tool to compare a multitude of starch derivatives with substituents of different polarity in various degrees of substitution to get tendencies regarding overall hydrophobicity. Moderate hydrophobic substitution was found to lead to a decrease of the efficient flocculant dose and to an increase of the flocculation window width. Amphiphilic starch derivatives with high DS of hydrophobic moieties showing strong hydrophobic association are effective only at significantly higher doses, but in a broader concentration range compared to cationic starch of the same DS. Joint analysis of adsorption isotherms and flocculation test data has revealed, that the surface coverage required to induce phase separation ranges between 10 and 25 % and is minimal for amphiphilic starch derivatives. This gave the evidence of the complex mechanism of flocculation via combination of electrostatic “charge patch” interactions and bridging. Concerning sticky reduction experiments by systematically studying the interactions between the novel amphiphilic starch derivatives and the model suspension it turned out, that dynamic surface tension is a very suitable property to characterize the surface active compounds in the model suspension giving additional information about the sticky potential of waste water, e.g. white water, being a new and sensitive method to describe the parameter “hydrophobicity”. Moderate cationic and hydrophobic starch derivatives have been proved to be the most effective ones for sticky removal.

The purpose of this study was to investigate the fundamental characteristics of a chelating surfactant in terms of solution behaviour, chelation of divalent metal ions, and interaction in mixtures with different foaming agents and divalent metal ion, as well as examining its prospects in some practical applications. Chelating surfactants are functional molecules, with both surface active and chelating properties, which are water soluble and therefore suitable for chelation in many aqueous environments. The dual functionality offers the possibility to recover the chelating surfactant as well as the metals. The DTPA (diethylenetriaminepentaacetic acid)-based chelating surfactant 4-C12-DTPA (2-dodecyldiethylenetriaminepentaacetic acid) was synthesized at Mid Sweden University. In the absence of metal ions, all eight donor atoms in the headgroup of 4-C12-DTPA are titrating and the headgroup charge can be tuned from +3 to -5 by altering the pH. The solution properties, studied by surface tension measurements and NMR diffusometry, were consequently found strongly pH dependent. pH measurements of chelating surfactant solutions as a function of concentration was used to extract information regarding the interaction between surfactants in the aggregation process. Small differences in the conditional stability constants (log K) between coordination complexes of DTPA and 4-C12-DTPA, determined by competition measurements utilizing electrospray ionization mass spectrometry (ESI-MS), indicated that the hydrocarbon tail only affected the chelating ability of the headgroup to a limited extent. This was further confirmed in hydrogen peroxide bleaching of thermomechanical pulp (TMP) treated with 4-C12-DTPA. Interaction parameters for mixed systems of 4-C12-DTPA and different foaming agents were calculated following the approach of Rubingh’s regular solution theory. The mixtures were also examined with addition of divalent metal ions in equimolar ratio to the chelating surfactant. Strong correlation was found between the interaction parameter and the phase transfer efficiency of Ni2+ ions during flotations. Furthermore, a significant difference in log K between different metal complexes with 4-C12-DTPA enabled selective recovery of the metal ion with the highest log K. The findings in this study contribute to the understanding of the fundamental characteristics of chelating surfactants, which can be further utilized in practical applications.

The research presented in this thesis was motivated by the desire to understand the flow field within a new digital microfluidic device currently under development. This required an investigation of the dynamics of a droplet migrating along the surface of another fluid due to interfacial surface tension gradients. The quantitative analysis of the flow field presented in this thesis provides the first known solution for the velocity field in a migrating droplet confined to an interface. The first step towards gaining insight into the flow field was accomplished by using the method of reflections to obtain an analytical model for a submerged droplet migrating near a free surface. The submerged droplet model enabled the analysis of the velocity field and droplet migration speed and their dependence on the fluid properties. In general, the migration velocity of a submerged droplet was found to differ dramatically from the classic problem of thermocapillary migration in an unbounded substrate. A boundary-collocation scheme was developed to determine the flow field and migration velocity of a droplet floating trapped at the air-substrate interface. The numerical method was found to produce accurate solutions for the velocity and temperature fields for nearly all parameters. This numerical scheme was used to judge the accuracy of the flow field obtained by the submerged droplet model. In particular, the model was tested using parameter values taken from a digital microfluidic device. It was determined that the submerged droplet model captured most of the flow structure within the microfluidic droplet. However, for a slightly different choice of parameters, agreement between the two methods was lost. In this case, the numerical scheme was used to uncover novel flow structures.

This thesis focuses on the lattice-Boltzmann method (LBM) and its ability to simulate immiscible two-phase flow. We introduce the main lattice-Boltzmann-based approaches for analyzing two-phase flow: the color-fluid model by Gunstensen, the interparticle-potential model by Shan and Chen, the free-energy model by Swift and Orlandini, and the mean-field model by He. The first objective is to assess the ability of these methods to maintain continuity at the interface of two fluids, especially when the two fluids have different viscosities or densities. Continuity issues have been mentioned in the literature but have never been quantified. This study presents a critical comparison of the four lattice-Boltzmann-based approaches for analyzing two-phase flow by analyzing the results of the two-phase Poiseuille flow for different viscosity ratios and density ratios. The second objective is to present the capability of the most recent version of the color-fluid model for simulating 3D flows. This model allows direct control over the surface tension at the interface. We demonstrate the ability of this model to simulate surface tension effects at the interface (Laplace bubble test), stratified two-phase flows Poiseuille two-phase flow), and bubble dynamics (the free rise of a bubble in a quiescent viscous fluid).

A project studied wetting of iron, nickel and platinum by molten MnO-SiO2 (MS) and CaO-Al2O3-SiO2 (CAS) slags of eutectic composition to contribute to understanding of wetting behaviour of solid metal-molten oxide systems relevant to steelmaking. Novel results of dynamic wetting behaviour by the sessile drop method were obtained under strongly reducing atmosphere (oxygen partial pressure 10-20 -- 10-18 atm). Terminal contact angles (after 240 min) for MS slag were: for iron substrates -5??2??(1350??C), 9+-2?? (1390??C), 6+-2 (1450??C); nickel -- 3+-2??(1350 and 1390??C); and platinum --15+-2??(1350 and 1390??C), 12+-2??(1450??C). Contact angles with CAS slag were: iron -- 55+-2??(1350??C), 60+-2?? (1390??C), 44+-2?? (1450??C); nickel -- 59+-2??(1350??C), 60+-2?? (1390??C); and platinum -- 15+-2?? (1350, 1390 and 1450??C). Values for interfacial tension, work of adhesion, spreading parameter (S) and interaction coefficient (Ф) were also determined. Work of adhesion for all three substrates with MS slag changed in a very narrow range 910 - 930 mJ/m2. Interfacial tension with this slag was 1,480 mN/m for Ni at 1350-1390??C, and 1,880-1,890 mN/m for Pt in the temperature range 1,350-1,450??C. For iron, interfacial tension was 1,720 mN/m at 1350??C (γ-Fe); it decreased to 1590-1580 mN/m with increasing temperature to 1390 and 1450??C (-Fe). Lower work of adhesion and higher interfacial tension was found for metals with CAS slag. Wetting properties of Pt substrate with MS slag were close to that with CAS slag, while Fe and Ni substrates showed better wetting by MS slag in comparison with CAS slag. This was attributed to higher reactivity of Fe and Ni with MS slag, particularly reduction of MnO. Although MnO was also reduced in reaction with Pt, oxygen adsorption in contact with both slags was a major factor governing wettability of Pt. Dissolution of manganese in nickel and platinum substrates at elevated temperatures modified the interface chemistry, causing formation of a liquid alloy phase. Degree of silica reduction from MS slag was much smaller in comparison with MnO reduction (negligible for Pt); it was very minor from CAS slag. Concentration profiles of Mn and Si across the interface and along the metal surface were used to estimate diffusion coefficients. Diffusion along metal surfaces was generally higher by 1 to 2 orders of magnitude than across the interface. Reduction of oxides and adsorption of oxygen modify the metal-oxide interface, making wetting dynamic. They have a profound on interfacial properties.

Thesis (MEng) -- Stellenbosch University, 2014 / ENGLISH ABSTRACT: The electrodynamics of arbitrary, point-to-plane electrospraying geometries, were investigated in this research both analytically and numerically. Electrospraying is the process during which particles of sizes in the nanometre range are simultaneously generated and charged by means of an applied electrostatic field. A high electrostatic potential is applied to a conductive capillary needle, which overcomes the force exerted by the liquid surface tension. One of the primary limitations of this process are corona discharges. The effect of corona discharges have not been studied quantitatively, even though it is frequently reported in the electrospraying literature. The main objective of this research was to understand the corona discharge thresholds associated with electrospraying. Previously, only one theoretical, and two empirical investigations studied this phenomenon, over a time period of approximately forty years. It was clear that by better understanding these thresholds, electrospraying could be applied much more effectively. A corona discharge threshold model is proposed, using either a numerical or analytical model for the calculation of polarization fields. When compared with the experimental results of other researchers, both these two models have average relative percentage errors of approximately 15%. These are the first models proposed in the literature for the calculation of electrospraying corona thresholds. A new method to determine surface tension using electrospraying is described theoretically. In addition to this method, the calculation of corona discharge thresholds have various applications. For example, the dynamics of electrostatic ion thrusters are much better described, powder production by means of electrospraying can be optimised, and pattern generation using pulsed electrospraying cone-jets can be optimised as well. / AFRIKAANSE OPSOMMING: Die elektrodinamika van arbitrêre, punt-tot-vlak elektrosproei geometrieë was beide analities en numeries ondersoek in hierdie tesis. Dit is die proses waartydens nanodeeltjies gelyktydig gegenereer en elektrostaties gelaai word. Deur 'n hoë elektriese potensiaal aan te lê tot 'n geleidende kapillêr, is dit moontlik om die krag van die oppervlakte spanning te oorkom. Een van die primêre beperkings van elektrosproei is corona ontladings. Die effek van corona ontladings was nog nie kwantitatief bestudeer nie, selfs al word dit dikwels rapporteer in die elektrosproei literatuur. Die primêre doel van hierdie navorsing was om die corona ontlading drempels te verstaan wat geassosieer word met elektrosproei. In die verlede was daar nog net een teoretiese, en twee empiriese ondersoeke gewees wat hierdie verskynsel bestuur het, oor 'n tydperk van ongeveer veertig jaar. Dit was duidelik dat deur 'n beter begrip te hê van hierdie elektrosproei drempels, kan hierdie proses baie meer doeltreffend toegepas word. In hierdie tesis word 'n corona ontlading drempel model voorgestel, wat gebruik maak van 'n analitiese of numeriese model om die polarisasie velde te bereken. Wanneer vergelyk met die resultate van ander navorsers, het beide die modelle 'n gemiddelde relatiewe persentasie fout van ongeveer 15%. Hierdie is die eerste modelle wat voorgestel word vir die berekening van corona ontlading drempels. Deur gebruik te maak van elektrosproei, word 'n nuwe metode ook voorgestel om die oppervlakte spanning te bereken. In byvoeging tot hierdie, het die berekening van corona ontlading drempels vele ander toepassings. As 'n voorbeeld, die dinamika van elektrostatiese ioon stuwers word beter beskryf, en poeier produksie deur middel van elektrosproei kan optimeer word.

L’interface air-eau est un milieu où la tension de surface intervient en permanence pour minimiser l’énergie de la surface. Cette force est à l’origine des phénomènes capillaires que les organismes semi-aquatiques exploitent. L’objectif de cette thèse est d’étudier l’importance de ces phénomènes dans l’écologie des organismes semi-aquatiques en prenant les gyrins comme modèle. Les résultats montrent que le ménisque bipolaire produit par les gyrins est responsable d’auto-assemblables statiques entre individus immobiles. Les gyrins utilisent également différents types de nage pour minimiser les forces de résistance qu’ils rencontrent, notamment la force liée à la production d’onde. L’étude expérimentale de la perception d’objets immobiles suggère la perception des ménisques par les gyrins. L’écholocation grâce aux ondes de surface, supposée dans la littérature, ne peut cependant être exclue. / The surface tension at the air-water interface is responsible for capillary phenomena minimizing surface energies. Semi-aquatic organisms have evolved to exploit this capillarity. The purpose of this thesis is to study the importance of capillary phenomena in the ecology of semi-aquatic organisms using whirligig beetles as a model. Results show that the bipolar meniscus produced around whirligig beetles is responsible for static self-assembly between individuals. These insects use different types of swimming to minimize resistance forces, especially the wave drag. The experimental study of the detection of immobile objects suggests that whirligig beetles perceive the menisci. Echolocation using surface waves, assumed in literature, cannot however be excluded.

The aim of this thesis is to find out using a method based on the size of the contact angle as changes over time surface free energy density polyethylene. Measured samples of discharges were adjusted by varying plasma and increased its surface tension. The theoretical part deals with the surface tension, contact angle and the Young's equation, which describes the relationship between wetting angle and energy at the interface states of matter. This work also mentions the ways in which the measurement is made. In the practical part of the thesis there is described not only the process of measuring, but also the own experiments and their results.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The addition of adjuvants can improve the quality of agricultural chemical sprays and have been an usual practice on the last years. The work presents two papers aiming to study the influence of adjuvant apply on the agricultural spray. The first article, entitled "Influence of adjuvants on the physicochemical characteristics of insecticides spray solution and electron microscope images of the deposits on wheat and corn leaves" evaluate changes in physical and chemical characteristics of the spray solution with the insecticides Thiamethoxam, Imidacloprid and Lambda-cyhalothrin. Were measured the surface tension, droplet contact angle on wheat and maize leaf, droplet coverage and images were made with a scanning electron microscope to better understand the deposit of these insecticides. Adjuvants alter the spray solution physical characteristics improving its wettability, furthermore, the addition of adjuvants may interfere with the deposit characteristics of the tested insecticides. The second article entitled "Tank-mix-adjuvants might improve deposit formation and cuticular penetration, and reduce rain-induced removal of chlorantraniliprole", aimed to verify the interaction of clorantraniliprole insecticide with commercial adjuvants. In this assay, have been studied aspects as adjuvant effect on the deposits formation, cuticular penetration through apple cuticles, droplet coverage and rain effect on the removal of the insecticide in wheat and maize crops. The results showed that the adjuvants play a crucial role in the hydrophobic cover sheet by changing the characteristics of the spray solution, thereby improving the wettability. Furthermore, adjuvants may enhance the absorption of clorantraniliprole insecticide. / A adição de adjuvantes pode melhorar a qualidade das pulverizações agrícolas e tem sido uma prática usual nos últimos anos. O presente trabalho apresenta dois artigos que tem como objetivo, estudar a influencia da utilização de adjuvantes nas pulverizações. O primeiro artigo, intitulado Influência de adjuvantes nas características físico-químicas de caldas de pulverização de inseticidas e imagens de microscópio eletrônico dos depósitos em folhas de trigo e milho avaliou as mudanças nas características físicas e químicas da calda de pulverização com os inseticidas tiametoxam, Imidacloprido e lambda-cialotrina. Sendo mensurada a tensão superficial, o ângulo de contato da gota, em folhas de trigo e milho, a cobertura de gotas e realizadas imagens com microscópio eletrônico de varredura. Os adjuvantes alteram as características físicas da calda, melhorando a sua molhabilidade, além disso, a adição de adjuvantes pode interferir nas características de formação do depósito dos inseticidas testados. O segundo artigo intitulado Tank-mix-adjuvants might improve deposit formation and cuticular penetration, and reduce rain-induced removal of chlorantraniliprole , objetivou verificar a interação do inseticida clorantraniliprole com adjuvantes comerciais. Foram estudados aspectos como efeito dos adjuvantes na formação dos depósitos, penetração cuticular, por meio de cutículas de maça, cobertura de gotas e efeito da chuva na remoção do inseticida, nas culturas do trigo e milho. Os resultados mostraram que os adjuvantes tem um papel essencial na cobertura de folhas hidrofóbicas, alterando as características da calda de pulverização e melhorando assim a molhabilidade da mesma. Além disso, se pode concluir que os adjuvantes podem melhorar a absorção do inseticida clorantraniliprole.

Submitted by RENATA THAYSA DA SILVA SANTOS null (renata_sol_2@hotmail.com) on 2017-09-19T19:23:31Z No. of bitstreams: 1 Dissertação pronta.pdf: 1297727 bytes, checksum: 9562b8aaaa9a30d19ffbb80afb4d3495 (MD5) / Approved for entry into archive by Monique Sasaki (sayumi_sasaki@hotmail.com) on 2017-09-20T17:21:48Z (GMT) No. of bitstreams: 1 santos_rts_me_bot.pdf: 1297727 bytes, checksum: 9562b8aaaa9a30d19ffbb80afb4d3495 (MD5) / Made available in DSpace on 2017-09-20T17:21:48Z (GMT). No. of bitstreams: 1 santos_rts_me_bot.pdf: 1297727 bytes, checksum: 9562b8aaaa9a30d19ffbb80afb4d3495 (MD5) Previous issue date: 2017-07-26 / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O espalhamento das gotas sobre superfícies vegetais pode indicar eficiência na aplicação de herbicidas. Porém, o espalhamento de uma gota depende das características da calda fitossanitária, especificamente das propriedades físico-químicas e as suas interações com as superfícies onde as gotas se depositam. As propriedades físicas, como tensão superficial e ângulo de contato podem ser alteradas pela adição de adjuvantes ao tanque do pulverizador. Assim, o desenvolvimento de pesquisas que avaliem a interação dos herbicidas associados a adjuvantes é importante para a recomendação correta do adjuvante, uma vez que o adjuvante pode proporcionar maior espalhamento da gota sobre a superfície de diferentes espécies de plantas, e potencializar o controle. Nesse sentido foram realizados dois estudos, sendo o primeiro para avaliar a tensão superficial e o ângulo de contato em três espécies do gênero Sida. No segundo foi avaliado o ângulo de contato de seis espécies de plantas daninhas e a relação do ângulo com o controle de Lantana camara e Crotalaria incana, de ocorrência em pastagem, ambiente vastamente cultivado no Brasil, mas no qual são raros os trabalhos desta natureza. Concluiu-se que a adição do adjuvante lecitina ao herbicida aminopiralide + fluroxipir reduz o ângulo de contato das gotas sobre as superfícies adaxial e abaxial de Sida cordifolia e Sida glaziovii. E quanto menor ângulo de contato maior controle das espécies avaliadas. / The spreading of the drops on plant surfaces may indicate the possible success in herbicide application. However, the spread of a drop depends on the characteristics of the spray solution, specifically the physicochemical properties and their interactions with the surfaces where the drops settle. Physical properties such as surface tension and contact angle can be altered by the addition of adjuvants to the spray tank. Thus, the development of research that evaluates the interaction of herbicides associated with adjuvants is important for the correct recommendation of the adjuvant, since the adjuvant can provide greater spreading of the drop on the surface of different species of plants, and potentiate the control. In this sense two studies were carried out, being the first to evaluate the surface tension and the contact angle in three species of the Sida genus. In the second, was evaluated the contact angle of six weed species and the angle relationship with the control of Lantana camara and Crotalaria incana, a pasture, an area widely cultivated in Brazil, but in which works of this nature are rare. It was concluded that the addition of the lecithin adjuvant to the aminopyralid herbicide + fluroxypyr reduces the contact angle of the drops on the adaxial and abaxial surfaces of Sida cordifolia and Sida glaziovii. And the lower the contact angle the greater the control of the evaluated species.