In dieser Arbeit wird eine neue Methode und ein neuartiges FET -Sensorelement zum Nachweis von Flüssigkeitsbewegungen vorgestellt, das zudem bei Bedarf auch als Chemo- oder Biosensor fungieren kann. Das Einsatzspektrum von FET-basierten Sensoren in Lab on a Chip-Systemen wird dadurch entscheidend erweitert. Bei dem entwickelten FET-Sensor Bauelement handelt es sich um einen normally-on n-leitenden Dünnschichtfeldeffekttransistor mit Ti-Au-Kontakten, basierend auf Silicon-on-Insulator- Substraten, wobei das natürliche Oxid des Siliziumfilms als Schnittstelle zum Elektrolyten bzw. zur Flüssigkeit verwendet wird. Der mit 10exp16 Bor Atomen pro cm³ p-dotierte Siliziumdünnfilm hat eine Dicke von nur 55 nm und ist durch eine 95 nm dicke Siliziumdioxidschicht vom darunterliegenden Siliziumsubstrat von 600 µm Dicke elektrisch isoliert. Aufgrund der geringen Schichtdicke durchdringt die feldempfindliche Raumladungs- bzw. Verarmungszone die gesamte Dünnschicht, so dass durch Anlegen einer Backgatespannung am Substrat der spezifische Widerstand und die Empfindlichkeit des Bauelements eingestellt werden können. Grundlegende ISFET-Funktionalitäten wie die Empfindlichkeit auf Änderungen der Ionenstärke und des pH-Wertes werden nachgewiesen und ein ENFET-Glukosesensor realisiert. Zudem wird im Hinblick auf die Separation von Emulsionen der Nachweis erbracht, dass die Benetzung mit Hexan und Toluol eine Änderung der spezifischen Leitfähigkeit bewirkt, und die Empfindlichkeit des Bauelements nach Beschichtung mit einem hydrophoben Methacrylatcopolymerfilm erhalten bleibt. Hinsichtlich der Verwendung des FET-Sensor Bauelements zum Nachweis von Flüssigkeitsbewegungen wird zunächst ein theoretisches Modell entwickelt, dessen Kernaussage ist, dass sich in einem rechteckigen Kanal der relative Bedeckungsgrad mit Flüssigkeit direkt proportional zum Drainstrom des FET-Sensors verhält. Basierend auf diesem theoretischen Modell, welches experimentell belegt wird, können mittels eines einzelnen FET-Sensors Füllstand und Füllgeschwindigkeit bzw. bei bekannter Füllgeschwindigkeit Kapillarvolumen und Kapillargeometrie bestimmt werden. Abweichungen von der direkten Proportionalität erlauben zudem, Rückschlüsse auf die Benetzungseigenschaften der Kapillaren und die Dynamik an der Halbleitergrenzfläche zu ziehen. Ist ein Sensorelement vollständig mit Flüssigkeit bedeckt, wird mittels Lösungsmitteltropfen als Markerobjekten die Strömungsgeschwindigkeit bestimmt. Ändert sich die Ionenkonzentration im Elektrolyten als Funktion der Strömungsgeschwindigkeit, so kann die Strömungsgeschwindigkeit durch Messung der Ionenkonzentration mittels FET-Sensor ebenfalls ermittelt werden. Als wichtigster Demonstrator für die Verwendung des FET-Sensors wird ein komplexes Lab on a Chip-System zur Separation von Emulsionen auf chemisch strukturierten Oberflächen entwickelt, bei dem der Separationsvorgang mittels FET-Sensorarray verfolgt werden kann. Zur einfachen Herstellung chemisch modifizierter Oberflächen für die Separationsexperimente werden die Abscheidung von nanoskaligen hydrophoben Methacrylatcopolymerfilmen und die selektive Fluorsilanisierung von Oberflächen sowie deren Lösungsmittelbeständigkeit in Wasser, Toluol und Aceton untersucht. Dabei zeigt sich, dass die Hydrophobie nach Lösungsmittelbehandlung weitestgehend erhalten bleibt, Wasserrückstände im Methacrylatfilm aber zu einer reversiblen Schichtdegradation führen können. Als Modellsystem werden Hexan-Wasser- bzw. Toluol-Wasser-Emulsionen verwendet, die auf Oberflächen getrennt werden, deren eine Seite hydrophil, und deren andere Seite hydrophob ist (Stufengradient). Der Separationsprozess beruht auf der großen Affinität des Wassers hin zu polaren Oberflächen, wobei das wenig selektive Lösungsmittel zur unpolaren Seite gedrängt wird. Zur Erlangung eines tieferen Verständnisses des Prozesses werden die Tropfenkoaleszenz und der Einfluss geometrischer Beschränkungen untersucht. Die Versuche werden sowohl auf offenen Oberflächen als auch im Spalt, unter Verwendung von hydrophilen und hydrophoben Oberflächen, durchgeführt. Es zeigt sich, dass sich die Dynamik der Tropfenkoaleszenz im Spalt umgekehrt zur Dynamik auf offenen Oberflächen verhält. Dies wird mittels eines hierzu entwickelten theoretischen Modells erklärt, welches die Minimierung der Oberflächenenergie und Hystereseeffekte einbezieht. Das Lab on a Chip-System schließlich besteht aus einem mit Siliziumnitrid beschichteten FET-Sensorchip, auf den eine Separationszelle aufgeklebt ist. Neben dem Einlass für die Emulsion ist ein weiterer Einlass vorhanden, durch den Salzsäure für eine pH-Reaktion zugegeben werden kann. Der gesamte Separationsprozess sowie die anschließende pH-Reaktion, lassen sich bequem am PC anhand der Änderung der Stromstärke der einzelnen Sensoren verfolgen und analysieren. Wichtige Ergebnisse hier sind: 1) Mittels eines quasi 1-dimensionalen Sensorarrays kann der Verlauf einer Flüssigkeitsfront in einem 2-dimensionalen Areal überwacht bzw. dargestellt werden. 2) Anhand der Signatur des Signalverlaufs bei pH-Änderung und Flüssigkeitsbewegung, können beide Prozesse unterschieden werden. Der Sensor kann also zum Nachweis von Flüssigkeitsbewegungen und zugleich als Chemosensor eingesetzt werden. Es wurde also nicht nur ein neuartiges, äußerst robustes, chemikalienbeständiges und biokompatibles Multifunktionssensorelement mit Abmessungen im Mikrometer- bis Millimeterbereich entwickelt, sondern auch eine neue Methode entwickelt, mit der es möglich ist, sowohl (bio-)chemische Reaktionen als auch die Bewegung von Flüssigkeiten in Lab on a Chip-Systemen nachzuweisen.

<p>The first part of this thesis is concerned with thestructure-property relationships in nonionic surfactantsystems. The main aim was to investigate how the surfactantstructure influences the adsorption at interfaces andinteractions between surfactant coated interfaces.Particularly, the effect of the structure of the surfactantheadgroups was investigated. These were sugar-based headgroupwith varying size and flexibility and poly(ethylene oxide)based headgroups with or without an additional amide or estergroup. The hydrophobic part of the surfactant consisted mostlyof straight alkyl chains, except for one type of poly(ethyleneoxide) based surfactant with a dehydroabietic hydrophobe.</p><p>The main technique that was used is the surface forcetechnique, with which the forces acting between two adsorbedsurfactant layers on hydrophilic or hydrophobic surfaces can bemeasured. These forces are important for e.g. the stability ofdispersions. The hydrophilic surfaces employed were glass andmica, whereas the hydrophobic surfaces were silanized glass andhydrophobized mica. The adsorption behavior on hydrophilicsurfaces is highly dependent on the type of headgroup andsurface, whereas similar results were obtained on the two typesof hydrophobic surfaces. To better understand how the surfaceforces are affected by the surfactant structure, measurementsof adsorbed amount and theoretical mean-field latticecalculations were carried out. The results show that the sugarsurfactant layers and poly(ethylene oxide) surfactant layersgive rise to very different surface forces, but that the forcesare more similar within each group. The structure-propertyrelationships for many other physical properties have beenstudied as well. These include equilibrium and dynamicadsorption at the liquid-vapor interface, micelle size, micelledynamics, and wetting.</p><p>The second part in this thesis is about the aggregationbetween cationic polyelectrolytes and an anionic surfactant.The surface force technique was used to study the adsorption ofa low charged cationic polyelectrolyte on mica, and theaggregation between the adsorbed polyelectrolyte with theanionic surfactant. The aggregation in bulk was studied withturbidimetry, small angle neutron scattering (SANS), and smallangle x-ray scattering (SAXS). An internal hexagonal aggregatestructure was found for some of the bulk aggregates.</p><p><b>Keywords:</b>nonionic surfactant, sugar surfactant,poly(ethylene oxide), amide, ester, polyelectrolyte, SDS,hydrophobic surface, glass surface, mica, adsorption,aggregation, micelle size, surface forces, wetting, dynamicsurface tension, NMR, TRFQ, SANS, SAXS, mean-field latticecalculations.</p>

In the last decade, there has been a growing interest in the use of differential sensing for molecular recognition. Inspired by the mammalian olfactory system, differential sensing employs an array of non-selective receptors, which through cross-reactive interactions, create a distinct pattern for each analyte tested. The unique fingerprints obtained for each analyte with differential sensing are studied with statistical analysis techniques, such as principal component analysis and linear discriminant analysis. It was postulated that serum albumin proteins would be applicable to differential sensing schemes due to significant differences in sequence identity between different serum albumin species, and due to the wide range of hydrophobic molecules which are known to bind to these proteins. Consequently, cross-reactive serum albumin arrays were developed, utilizing hydrophobic fluorescent indicators to detect hydrophobic molecules. As such, serum albumin cross-reactive arrays were employed to discriminate subtly different hydrophobic analytes, and mixtures of these analytes, in the form of terpenes and perfumes, plasticizers and plastic explosive mixtures, and glycerides and adipocyte extracts. In this doctoral work, a detailed review of the field of differential sensing, and a thorough study of principal component analysis and linear discriminant analysis in various differential sensing scenarios, are given. These introductory chapters aid in better understanding the methods and techniques applied in later experimental chapters. In chapter 3, serum albumins, a PRODAN indicator, and an additive are shown to discriminate five terpene analytes and terpene doped perfumes. Chapter 4 describes an array with serum albumins, two dansyl fluorophores, and an additive which successfully differentiate the plasticizers found within the plastic explosives C4 and Semtex and simulated C4 and Semtex mixtures. Discrimination of these simulated mixtures was also achieved with this array in the presence of soil contaminants, demonstrating the potential real-world applicability of this sensing ensemble. Finally, chapter 5 details an array consisting of serum albumins, several fluorescent indicators, and a Grubb's olefin metathesis reaction, to differentiate saturated and unsaturated triglycerides, diglycerides, and monoglycerides. Mixtures of glycerides in adipocyte extracts taken from rats with different health states were then successfully discriminated, showing promise for clinical applications in differentiating adipoctyes from pre-diabetic, type 2 diabetic, and non-diabetic individuals. / text

From the Proceedings of the 1972 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - May 5-6, 1972, Prescott, Arizona / The need for increased control of seepage from both natural and artificial small ponds and lakes has become more apparent with the increased frequency of their construction and use on the farm, ranch, and in recreational urban use. Seepage control methods are also becoming more numerous. Unfortunately, comparisons as to effectiveness, longevity and costs are not readily available. This paper investigates some control techniques being used in this region and evaluated them according to the above criteria. Emphasis was on the use of available physiochemical methods other than rubber membranes and concrete liners. Examples of the types of controls in use include plastic, soil compaction aids, hydrophobic chemicals and monovalent cation applications, such as sodium chloride. Some examples of the use of these methods in Arizona are shown and the results of some field comparison tests conducted using 8 x 8 square foot double -ringed infiltrometers presented. Recommendations are made of additional research that should be undertaken to improve the technology of the control of seepage losses.

From the Proceedings of the 1973 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - May 4-5, 1973, Tucson, Arizona / An infiltration- wetting agent study, using the wetting agent "WATER-IN", was conducted in the ponderosa pine forest type of east central Arizona. An application rate of 10 gallons of wetting agent per acre was used on bare mineral soil and on ponderosa pine litter. The infiltration rate was measured by a modified North Fork infiltrometer. It was found that "WATER-IN" significantly increased water runoff when applied to litter, but, when applied to bare mineral soil, "WATER-IN" caused a significant increase in water infiltration. The wetting agent did not significantly affect antecedent moisture, soil particle distribution, litter water holding capacity, or litter bulk density. It is presently hypothesized that the increase in water infiltration on treated bare mineral soil is due to a decrease in the average bulk density of the surface inch of soil. The increase in runoff when litter is treated is probably due to an interaction, either physical, chemical, or both, between the humus layer and "WATER-IN ", creating a hydrophobic condition where one did not exist before.

Στην εργασία αυτή μελετήθηκε η ρόφηση και η εκρόφηση του παρασιτοκτόνου ατραζίνη (atrazine) σε πρότυπες εδαφικές ουσίες καθώς και σε ένα τυπικό δείγμα εδάφους, τόσο σε αντιδραστήρες διαλείποντος έργου (batch) όσο και σε πληρωμένες κλίνες (bed). Ως πρότυπες ουσίες επιλέχθηκαν η πυριτία (silica-gel, SiO2), η αλούμινα (γ-alumina, Al2O3), το ανθρακικό ασβέστιο (calcite, CaCO3) και το χουμικό οξύ (humic acid). Η ατραζίνη ροφείται σημαντικά στο χουμικό οξύ στην πυριτία και στο έδαφος, όμως βρέθηκε ότι έχει πολύ μεγαλύτερη συγγένεια για το χουμικό οξύ σε σύγκριση με την πυριτία. Η ατραζίνη δεν έδειξε να ροφείται στη γ-αλούμινα και το CaCO3, ανεξαρτήτως από τις πειραματικές συνθήκες που χρησιμοποιήθηκαν. Σε όλες τις περιπτώσεις, η κινητική μελέτη έδειξε δύο διακριτά στάδια: ένα πρώτο γρήγορο στάδιο ρόφησης της ατραζίνης, διαδεχόμενο από ένα δεύτερο πιο αργό στάδιο. Η κινητική της ρόφησης υπακούει ικανοποιητικά στο μοντέλο Elovich. Στα χρονικά πλαίσια που μελετήθηκε η ρόφηση και η εκρόφηση, η διεργασία είναι αντιστρεπτή και η ατραζίνη εκροφείται ποσοτικά. Οι ισόθερμοι ρόφησης της ατραζίνης λήφθηκαν σε διαφορετικές τιμές ιοντικής ισχύος, pH και θερμοκρασίας και υπακούουν στο μοντέλο Freundlich. Σε όλες τις περιπτώσεις που μελετήθηκαν, η αύξηση της ιοντικής ισχύος του διαλύματος προκάλεσε αύξηση της ροφημένης ποσότητας της ατραζίνης. Η ρόφηση της ατραζίνης μειώνεται καθώς το pH του διαλύματος αυξάνεται. Όσον αφορά στην πυριτία, η ρόφηση της ατραζίνης φαίνεται ότι γίνεται κυρίως μέσω δεσμών υδρογόνου με τις υδροξυλομάδες της επιφάνειας. Όσον αφορά στο χουμικό οξύ, το σημαντικότερο ρόλο στη ρόφηση παίζει η διάχυση της ατραζίνης προς το εσωτερικό του στερεού όπου η ρόφηση επιτυγχάνεται κυρίως μέσω υδρόφοβων αλληλεπιδράσεων. Η προσρόφηση της ατραζίνης στην πυριτία αυξάνεται σημαντικά καθώς αυξάνεται η θερμοκρασία του διαλύματος, μια τάση που δεν παρατηρείται κατά τη ρόφηση της ατραζίνης στο χουμικό οξύ. Η θερμοδυναμική ανάλυση έδειξε ότι η ρόφηση στα μοντέλα εδάφους είναι φυσική αφού παρατηρήθηκαν τιμές της ενθαλπίας ρόφησης στην περιοχή των 10 kJ mol-1. Οι λαμβανόμενες ισόθερμοι ρόφησης από τα πειράματα σε πληρωμένες κλίνες ήταν σε καλή συμφωνία με αυτές που λήφθηκαν από τα πειράματα στους αντιδραστήρες διαλείποντος έργου. Η παρουσία χουμικού οξέος στις κλίνες προκαλεί με το χρόνο δραστική μείωση της διαπερατότητας. / Adsorption and desorption of the herbicide atrazine was investigated on the principal inorganic constituents of soil, as well as on a typical Greek soil sample. The studies were conducted both in batch, stirred reactors and in packed beds. Silica-gel (SiO2), γ-alumina (Al2O3) and calcite (CaCO3), were selected as model inorganic substances. Humic acid was selected as a model substance representative of the organic part of soil. Significant adsorption of atrazine was measured on the humic acid, silica and on the soil suspensions in electrolyte solutions. Atrazine exhibited higher affinity for humic acid rather than for silica. Atrazine did not adsorb on γ-alumina and on CaCO3 regardless the experimental conditions (pH range or total solid available for adsorption). In all cases, kinetic results have shown two distinct features: a first, fast sorption step, followed by a second, slow step. The kinetics data of atrazine uptake on both substrates yielded satisfactory fit to the Elovich model. Atrazine was found to be completely desorbed from both the humic acid and the silica substrates. Adsorption isotherms for atrazine were obtained at different values of ionic strength, pH and temperature. The adsorption data gave the best fit to the Freundlich model. In all cases investigated, the amount of adsorbed atrazine increased upon increasing the ionic strength of the solution. The adsorption of atrazine decreased with increasing solution pH. The adsorption of atrazine on silica was primarily dominated by the formation of hydrogen bonds with the surface hydroxyl groups. In the case of humic acid, the diffusion of atrazine to the interior of the solid seemed to play the most significant role. Inside the organic substance particles, sorption took place mainly through hydrophobic interactions. The sorption of atrazine on silica surface increased considerably with increasing temperature, a trend not found in the case of humic acid. The thermodynamic analysis yielded adsorption energy values of the order of 10 kJ mol-1 suggesting physical adsorption. The isotherms obtained from the packed bed experiments were in a good agreement with those obtained from batch experiments. Finally, humic acid grains, mixed with silica in packed beds, were found to change morphology upon hydration which resulted to swelling. The humic substances clogged a large portion of the pores of the packed beds, decreasing drastically their permeability.

The main aim of this thesis was to characterize membrane-solute interactions using artificial membranes in immobilized liposome chromatography or capillary electrophoresis. The partitioning of a solute into a cell membrane is an essential step in diffusion across the membrane. It is a valid parameter in drug research and can be linked to the permeability as well as the absorption of drugs. Immobilized liposome chromatography was also used to study partitioning of lignin precursor models. Lignin precursors are synthesized within plant cells and need to pass the membrane to be incorporated into lignin in the cell wall. In immobilized liposome chromatography, liposomes or lipid bilayer disks were immobilized in gel beads and the partitioning of solutes was determined. Capillary electrophoresis using disks as a pseudostationary phase was introduced as a new approach in drug partitioning studies. In addition, octanol/water partitioning was used to determine the hydrophobicity of the lignin precursor models. Electrostatic interactions occurred between bilayers and charged drugs, whereas neutral drugs were less affected. However, neutral lignin precursor models exhibited polar interactions. Moreover, upon changing the buffer ionic strength or the buffer ions, the interactions between charged drugs and neutral liposomes were affected. Hydrophobic interactions were also revealed by including a fatty acid or a neutral detergent into the bilayer or by using a buffer with a high salt concentration. The bilayer manipulation had only a moderate effect on drug partitioning, but the high salt concentration had a large impact on partitioning of lignin precursor models. Upon comparing the partitioning into liposomes and disks, the latter showed a more pronounced partitioning due to the larger fraction of lipids readily available for interaction. Finally, bilayer disk capillary electrophoresis was successfully introduced for partitioning studies of charged drugs. This application will be evaluated further as an analytical partitioning method and separation technique.

This thesis examined the use of two-phase partitioning bioreactors (TPPBs) for the biodegradation of poorly water-soluble compounds. TPPBs are stirred tank bioreactors composed of a biocatalyst-containing aqueous phase and an immiscible second phase containing large amounts of poorly water-soluble or toxic substrates. Degradation of the bioavailable substrate in the aqueous phase will result in equilibrium-driven partitioning of additional substrate from the immiscible phase into the aqueous phase, theoretically allowing for complete substrate degradation. Fundamental work was undertaken with the PCB-degrading organisms Burkholderia xenovorans LB400 in liquid-liquid and solid-liquid TPPBs. Initially biphenyl was used as the sole carbon source due to its hydrophobic nature and structural similarity to the environmentally relevant PCBs. The critical LogKO/W (octanol/water partitioning coefficient) of the organism was determined to be 5.5 and its growth kinetics on biphenyl were determined in a liquid-liquid TPPB. A polymer selection strategy for solid-liquid TPPBs was developed in the next chapter, and it was shown in the following chapter that biphenyl degradation in solid-liquid TPPBs was mass transfer limited, as described mathematically utilising the previously estimated microbial kinetics. The fundamental knowledge gained in the early chapters was then applied to the degradation of PCBs by the same organism. It was shown that the aqueous phase availability of PCBs is the rate-limiting step in biphasic bioreactors, and not the mass transfer rate. The low specific microbial degradation rates, resulting from substrate-limited growth were addressed with increased biomass concentrations; however, it was also found that an additional carbon source was required to maintain microbial activity over an extended period of time. Pyruvic acid was selected as a carbon source which, once added to actively PCB-degrading cells, maintained the cells’ activity towards PCBs and up to 85 % of 100 mg l-1 was degraded in 15 h. It was shown as the final contribution in this thesis that TPPBs can be combined with a PCB soil extraction step as a potential remediation scheme for PCB contaminated soil. PCBs were extracted from soil with polymer beads (up to 75 % removal), followed by biodegradation of the PCBs in a solid-liquid TPPB in which PCBs were delivered to the degrading organism from the same polymer. / Thesis (Ph.D, Chemical Engineering) -- Queen's University, 2007-08-07 16:11:00.494

The hydrophobicity of a surface is an important property in many areas of science and engineering. This is especially the case in mineral processing, where differences in surface hydrophobicity lie at the heart of the separation process of flotation. Chemicals are used to increase and decrease the natural hydrophobicity of minerals to attain a better separation between valuable and worthless material. Polymers are often used to reduce mineral surface hydrophobicity. Decades of empirically based decision making have produced a list of effective depressants. However the detailed study of how these polymer depressants affect surface hydrophobicity and mineral recovery lags behind applied investigations. The aim of this thesis was to study the adsorption of commonly used depressants on model surfaces and to interrogate the action of these polymers in reducing surface hydrophobicity. We have modelled the degree of hydrophobicity of common minerals in order to study polymer depressants with methods not commonly used in studies of surface characterisation in flotation. The model surfaces (self-assembled monolayers, SAMs) allowed us to use the quartz crystal microbalance with dissipation monitoring (QCM-D) to study the adsorption of polymers. The QCM-D can be used to obtain adsorption isotherms, adsorption kinetics, water content of adsorbed layers, and information on the conformation of the adsorbed polymer. The results from the QCM-D were correlated with the contact angle data from the captive bubble measurements, with which we assessed the hydrophobicity of the surface before and after polymer adsorption. Three of the polymers layers were probed with dynamic dewetting studies, in order to test other modes of depressant action. Three types of polymers were studied - a polyacrylamide (Polymer-H), a polyelectrolyte CMC (carboxymethyl cellulose) and a group of dextrins (Dextrin-TY, a phenyl succinate substituted dextrin (PS Dextrin) and a styrene oxide substituted dextrin (SO Dextrin)). These polymers are commonly used or have potential to be used in the depression of talc and graphite. Polymer-H was used to investigate the hydrophobic bonding between a non-ionic polymer depressant and chemically inert and non charged surfaces by probing the influence of substrate hydrophobicity on polymer adsorption and reduction of contact angle. Three different model surfaces were used (mixed self-assembled 0.5 SAM, 0.7 SAM or single self-assembled 1.0 SAM monolayers) with advancing contact angles between 75?? and 119??. The study of Polymer-H found that the substrate hydrophobicity is an important factor in adsorption of this polymer and the change in contact angle upon adsorption depends on adsorbed amount. The effectiveness of Polymer-H to reduce surface hydrophobicity was established to correlate with its conformation and morphology. CMC was investigated to find out how a stimulus responsive polymer depressant can be used in flotation. It was established that the adsorbed amount and rate of adsorption of CMC increase with decreasing of pH or increasing of ionic strength. It was shown that the surface hydrophobicity of a CMC pre-adsorbed layer changes with the environment and these alterations are fully reversible. A switch of ionic strength (from 10-2 M KCl to 10-1 M KCl) caused partial dehydration of the adsorbed layer and a decrease of the receding contact angle by 20??. A pH switch (pH = 9 to pH = 3) resulted in a 40?? change in receding contact angle. The CMC investigation showed that the use of a stimulus responsive polymer presents opportunities for exploiting solution conditions as a means to effect a better mineral separation in flotation The adsorption of three dextrin-based polymers on a model hydrophobic surface has been characterized using the quartz crystal microbalance with dissipation monitoring (QCM-D). The three polymers (one standard dextrin and two dextrins with different aromatic group substitutions) exhibited varying affinities and capacity for adsorption on the hydrophobic substrate. The effect of the three polymers on the static contact angle of the surface was studied using captive bubble contact angle measurements. The three polymers were seen to reduce the receding contact angle by similar amounts (approximately 14 degrees) in spite of having varying adsorbed amounts and differences in adsorbed layer water content. Although no differences were observed in the ability of the polymers to reduce the static contact angle, measurements of the dewetting dynamics between a rising air bubble and the polymer covered substrate yielded stark differences between the polymers, with one polymer slowing the dewetting dynamics by an order of magnitude more than the other two polymers. The differences in dewetting behaviour correlate with the adsorbed layer characteristics determined by QCM-D. / Thesis (PhD)--University of South Australia, 2010

Solid surfaces featuring a spatial variation of surface wettability along particular directions on their surface, referred to as wettability gradient surfaces, are becoming increasingly important in practical applications such as enhancement of boiling and condensation heat transfer and separation of immiscible liquids in smart micro-fluidic devices. With the aid of an external energy input, such as mechanical vibration or impact kinetic energy, a liquid drop on such surfaces gets propelled towards more wettable region on the surface. A fundamental study of impact dynamics of liquid drops on such solid surfaces is relevant in understanding their effectiveness. The present thesis reports a combined experimental and theoretical study on the impact dynamics of liquid drops on solid surfaces comprising a smooth portion and a groove-textured portion separated by a junction line (dual-textured surfaces). Three different dual-textured surfaces – two made of intrinsically hydrophilic stainless steel and one of intrinsically hydrophobic poly-di-methyl-siloxane (PDMS) – are considered. Liquid drops, with Weber number (We) in the range 1–100, are impacted on the junction of the dual-textured surfaces and the entire impact dynamics across the junction is captured using a high speed video camera. Experiments of drop impact on the homogeneous surface portions of dual-textured surfaces (far away from the junction) are also conducted. The temporal variation of drop contact radius measured from the junction line on smooth and groove-textured portions of the dual-textured surfaces exhibits four distinct stages – primary spreading, primary receding, secondary spreading on more wettable surface portion, and final equilibrium – with the final outcome being the bulk movement and deposition of liquid drop away from the junction towards the more hydrophilic surface portion. Secondary parameters characterizing each of these different stages are extracted from these measurements and a one-to-one comparison between dual-textured and homogenous surfaces is presented. A significant effect of dual-texture nature is seen on the receding process of impacting drops. On the dual-textured surfaces, the receding velocity of impacting drop on the groove-textured portion is always greater than that on the smooth portion. The asymmetry in drop receding results in a drop drift velocity towards the more wettable surface portion leading to an enhanced secondary drop spreading on the more wettable smooth portion. The drop drift velocity shows a decrease with We at low We and remains almost constant at higher We after a particular value of We. Correspondingly, the ratio of the maximum drop spread factor achieved during the secondary spreading (βm2) to that during the primary spreading (βm) is seen to decrease with We at low We and remains constant at higher We. Owing to the differences in the static equilibrium wetting difference, βm2/βm is more on the stainless steel dual-textured surfaces than on the PDMS dual-textured surface. The presence of dual-texture results in a higher final spread on more wettable smooth portion and smaller final spread on less wettable textured portion of the dual-textured surfaces and this difference decreases with We. The difference in final spread factors between the smooth and textured portions is more on the stainless steel dual-textured surfaces than the PDMS dual-textured surface. The bulk drop movement (ξ), characterized in terms of distance measured from the junction to the final drop center, decreases with We at low We and remains constant at higher We on the stainless steel dual-textured surfaces whereas it remains constant at low We and decreases at higher We on the PDMS dual-textured surface. ξ on the PDMS dual-textured surface is always less than that on the stainless dual-textured surface due to the lower wetting difference across the junction of the former. Comparison of the trends of secondary parameters with the predictions from theoretical models reported in literature showed a lack of agreement. This is due to various physical processes encountered by impacting drop on the groove-textured surface, identified through experiments of drop impact on homogeneous groove-textured surfaces, such as (i) convex shape of liquid-vapor interface near contact line at maximum spreading, (ii) impregnation of drop liquid into the grooves during impact, and (iii) contact line pinning of spreading drop at the asperity edges of surface texture, as well as the wetting difference in dual-textured surfaces. The inclusion of these physical processes under conventional energy conservation approach is seen to predict the experimentally observed trends of maximum drop spread factor on the groove-textured portions. A force balance model, applied to the liquid drop configuration at the beginning of drop receding on the dual-textured surfaces, predicts the qualitative trend of ξ with We on all surfaces. Drop liquid impregnation into the grooves of textured portion at We > Wecr (critical We corresponding to transition from Cassie to impaled state) is proposed as a possible physical mechanism to account for the explanation of the specific trends of ξ with We. A theoretical model formulated using force balance at the three phase contact line beneath impacting drop on groove-textured surface is presented for the prediction of Wecr.