This study deals with the association of trace elements with colloids and particles in surface waters and groundwaters of mining and smelting district of Příbram. Colloids were studied using combination of cascade filtration a tangential flow ultrafiltration method to separate individual colloid fractions. Colloids were separated by filtration membranes with nominal pore size 0,8 μm, 0,45 μm, 0,1 μm, 100 kDa, and 5 kDa. Water samples were analyzed using ICP-OES, ICP-MS and HPLC. The data were used for thermodynamic modeling using PHREEQC-2 programme. The results show that major and trace elements can be divided into several groups, based on their abundance in individual size fractions. Most elements dominate in fraction of truly dissolved matter as dissociated ions (< 5 kDa), maximum concentration in colloid fraction is 5-20 % and almost exclusively in fraction 5 kDa - 100 kDa. Gradual decrease of concentration in all fractions at low ionic strength (1,2 mmol/l) was observed in case of elements such as As, Co, Cr, Si, Sb and U. Gradual decrease of concentration in several samples was observed for Cd, Fe, Pb, Mn and Zn. Dominant binding to colloids and particles in surface waters was observed for Fe and Pb, where these fractions accounted for over 90 %. The main factor influencing colloid...

In dieser Arbeit wurde die Rolle selektiver, nicht-kovalenter Wechselwirkungen bei der Selbstorganisation von Diblockcopolymeren untersucht. Durch Einführung elektrostatischer, dipolarer Wechselwirkungen oder Wasserstoffbrückenbindungen sollte es gelingen, komplexe Mesostrukturen zu erzeugen und die Ordnung vom Nanometerbereich auf größere Längenskalen auszuweiten. Diese Arbeit ist im Rahmen von Biomimetik zu sehen, da sie Konzepte der synthetischen Polymer- und Kolloidchemie und Grundprinzipien der Strukturbildung in supramolekularen und biologischen Systemen verbindet. Folgende Copolymersysteme wurden untersucht: (i) Blockionomere, (ii) Blockcopolymere mit chelatisierenden Acetoacetoxyeinheiten und (iii) Polypeptid-Blockcopolymere. / In this work, the basic principles of self-organization of diblock copolymers having the in&#172;herent property of selective or specific non-covalent binding were examined. By the introduction of electrostatic, dipole&ndash;dipole, or hydrogen bonding interactions, it was hoped to add complexity to the self-assembled mesostructures and to extend the level of ordering from the nanometer to a larger length scale. This work may be seen in the framework of biomimetics, as it combines features of synthetic polymer and colloid chemistry with basic concepts of structure formation applying in supramolecular and biological systems. The copolymer systems under study were (i) block ionomers, (ii) block copolymers with acetoacetoxy chelating units, and (iii) polypeptide block copolymers.

Kolloidpartikel die von zwei nicht mischbaren Fluiden benetzt werden, tendieren dazu sich an der fluiden Grenzfläche aufzuhalten um die Oberflächenspannung zu minimieren. Bei genügender Anzahl solcher Kolloide werden diese zusammengedrückt und lassen die fluide Grenzfläche erstarren. Das gesamte System aus Fluiden und Kolloiden bildet dann eine spezielle Emulsion mit interessanten Eigenschaften. In dieser Arbeit wird ein kontinuum Model für solche Systeme entwickelt, basierend auf den Prinzipien der Massenerhaltung und der themodynamischen Konsistenz. Dabei wird die makroskopische Zwei-Phasen-Strömung durch eine Navier-Stokes Cahn-Hilliard Gleichung modelliert und die mikroskopischen Partikel an der fluiden Grenzfläche durch einen Phase-Field-Crystal Ansatz beschrieben. Zur Evaluation des verwendeten Strömungsmodells wird ein Test verschiedener Navier-Stokes Cahn-Hilliard Modelle anhand eines bekannten Benchmark Szenarios durchgeführt. Die Ergebnisse werden mit denen von anderen Methoden zur Simulation von Zwei-Phasen-Strömungen verglichen. Desweiteren wird eine neue Methode zur Simulation von Zwei-Phasen-Strömungen in komplexen Gebieten vorgestellt. Dabei wird die komplexe Geometrie implizit durch eine Phasenfeldvariable beschrieben, welche die charakteristische Funktion des Gebietes approximiert. Die Strömungsgleichungen werden dementsprechend so umformuliert, dass sie in einem größeren und einfacheren Gebiet gelten, wobei die Randbedingungen implizit durch zusätzliche Quellterme eingebracht werden. Zur Einarbeitung der Oberflächenkolloide in das Strömungsmodell wird schließlich die Variation der freien Energie des Gesamtsystems betrachtet. Dabei wird die Energie der Partikel durch die Phase-Field-Crystal Energie approximiert und die Energie der Oberfläche durch die Ginzburg-Landau Energie. Eine Variation der Gesamtenergie liefert dann die Phase-Field-Crystal Gleichung und die Navier-Stokes Cahn-Hilliard Gleichungen mit zusätzlichen elastischen Spannunngen. Zur Validierung des Ansatzes wird auch eine sharp interface Version der Gleichungen hergeleitet und mit der zuvor hergeleiteten diffuse interface Version abgeglichen. Die Diskretisierung der erhaltenen Gleichungen erfolgt durch Finiten Elemente in Kombination mit einem semi-impliziten Euler Verfahren. Durch numerische Simulationen wird die Anwendbarkeit des Modells gezeigt und bestätigt, dass die oberflächenaktiven Kolloide die fluide Grenzfläche hinreichend steif machen können um externen Kräften entgegenzuwirken und das gesamte System zu stabilisieren. / Colloid particles that are partially wetted by two immiscible fluids can become confined to fluidfluid interfaces. At sufficiently high volume fractions, the colloids may jam and the interface may crystallize. The fluids together with the interfacial colloids compose an emulsion with interesting new properties and offer an important route to new soft materials. Based on the principles of mass conservation and thermodynamic consistency, we develop a continuum model for such systems which combines a Cahn-Hilliard-Navier-Stokes model for the macroscopic two-phase fluid system with a surface Phase-Field-Crystal model for the microscopic colloidal particles along the interface. We begin with validating the used flow model by testing different diffuse interface models on a benchmark configuration for a two-dimensional rising bubble and compare the results with reference solutions obtained by other two-phase flow models. Furthermore, we present a new method for simulating two-phase flows in complex geometries, taking into account contact lines separating immiscible incompressible components. In this approach, the complex geometry is described implicitly by introducing a new phase-field variable, which is a smooth approximation of the characteristic function of the complex domain. The fluid and component concentration equations are reformulated and solved in larger regular domain with the boundary conditions being implicitly modeled using source terms. Finally, we derive the thermodynamically consistent diffuse interface model for two-phase flow with interfacial particles by taking into account the surface energy and the energy associated with surface colloids from the surface PFC model. The resulting governing equations are the phase field crystal equations and Navier-Stokes Cahn-Hilliard equations with an additional elastic stress. To validate our approach, we derive a sharp interface model and show agreement with the diffuse interface model. We demonstrate the feasibility of the model and present numerical simulations that confirm the ability of the colloids to make the interface sufficiently rigid to resist external forces and to stabilize interfaces for long times.

‘Soft condensed matter’ is a newly-emerged sub-discipline of physics concerned with the study of systems that are mechanically soft such as colloids, emulsions, surfactants, polymers, liquid crystals, granular media and various biomaterials including DNA and proteins. These materials display a broad range of interesting microstructures and phase behaviours and have a myriad of applications in the materials, food, paint and cosmetic industries as well as medical technologies. Soft condensed matter physics presents new opportunities and challenges for the development of new ideas and concepts in experimental and theoretical physics alike. Because the field overlaps with many different disciplines, the study of soft matter also offers promising developments to other fields of science including chemistry, chemical engineering, materials science, biology, and environmental science. The behaviour of these systems is dominated by one simple fact: they contain mesoscopic structures in the size range 10 nm to 1 µm that are held together by weak entropic forces. The elastic constants of these materials are 109 times smaller than the conventional atomic materials and hence are easily deformable by external stresses, electric or magnetic fields, or even by thermal fluctuations. We have studied two important classes of soft matter systems in this thesis -colloidal suspensions and surfactant systems. The thesis is divided into two main themes: (a) Effects of electric field on the colloidal suspensions, and (b) Effects of shear on surfactant solutions. Motions of colloidal particles under the influence of applied electric field were observed under a microscope and were studied using image analysis and particle tracking. We have also used tracking of thermal fluctuations of colloidal particles embedded in surfactant gels to study microrheology of surfactant solutions. Linear and non-linear rheology of aqueous solutions of cationic cetyltrimethyl ammonium bromide (CTAB) and anionic sodium-3-hydroxynapthalene-2-carboxylate (SHNC) were studied using bulk rheology in a commercial rheometer. Rheological studies of an anionic surfactant sodium dodecyl sulphate (SDS) in the presence of strongly binding counterion p-toluidine hydrochloride (PTHC) has also been done. Chapter 1 starts with a general introduction to soft condensed matter systems and then we proceed to describe two specific class of soft condensed materials which we have studied in this thesis -colloidal suspensions and surfactant/water systems. After describing different types of colloids, we discuss why colloids are suitable as model systems in condensed matter physics. This is followed by a discussion on the chemical structure, phase behaviour and self assembling properties of surfactant molecules in water. We then discuss the inter-macromolecular forces such as van der Waals interaction, the screened Coulomb repulsion, hydrogen bond, hydrophobic and hydration forces and steric repulsion which are the major players in the interaction in soft condensed matter systems. The systems that have been the subject of our experimental studies, viz. polystyrene colloidal suspensions, CTAB+SHNC, SDS+PTHC and CTAT have also been discussed in detail. Then we have given an overview of effects of electric field on the colloidal suspensions. Two types of geometries have been discussed: one in which the field is parallel to the plates and another when the field is perpendicular to the electrodes. Application of colloidal particles in diagnostic tests (Latex Agglutination Tests) has been discussed after this. Some methods used to enhance the sensitivity of LATs have also been reviewed. This is followed by a theoretical background of linear and non-linear rheology. We have also given an introduction to digital video microscopy, its advantages and discussed few quantities like pair correlation function, structure factor which can be extracted using digital video microscopy and particle tracking. The concluding part of this chapter describes the organization of this thesis. Chapter 2 discusses the experimental apparatus and techniques used in our studies. We describe our setup for applying the electric field to the colloidal particles and imaging and tracking their motion. We also discuss the image processing and analyzing methods for extracting the useful quantities from the digitized images. We have described the various components of the MCR-300 stress-controlled rheometer (Paar Physica, Germany) and the AR-1000N stress-controlled rheometer (T. A. Instruments, U. K.) followed by different experimental geometries that we have used for our experiments. Next we have described the various experiments that can be done using a commercial rheometer. Calculation of surface charge of colloidal particles using a conductivity meter has been demonstrated for our colloidal particle suspensions. We also describe the sample preparation methods employed in different experiments. In Chapter 3, we have discussed our study of clustering of colloidal particles under the influence of an ac electric field as a function of frequency. The field was applied in a direction perpendicular to the confining walls. Two regimes are observed, a low frequency regime where the clusters are isotropic with a local triangular order and a new high-frequency regime where the clusters are highly elongated (anisotropic) with no local order. The crossover from one regime to the other occurs at a critical frequency, fc. The formation of elongated clusters seen at high frequencies is explained in terms of rotation of particles due to a phase lag between the polarization of the electric double layer around a particle and the applied electric field that arises because of inhomogeneities of the conducting surface. We have also observed that the threshold field for the cluster formation, Eth, increases with frequency in both the regimes. We did these studies on two different sizes of particles and found that both Eth and fc were lower for the larger particles. Our model based on particle rotation was able to estimate the value of fc correctly for both the sizes of the particles. Chapter 4 describes a method employing an ac electric field applied perpendicular to the confining walls to increase the sensitivity of recognition of ligands by their corresponding receptors grafted on Brownian latex particles. Application of electric field assists the colloidal micro-particles grafted with receptors to come nearer due to electro-hydrodynamic drag. This increase in the local concentration of the latex particles results in improving the chances of ligand-receptor interaction leading to the aggregation of the latex particles. With this technique we have been able to increase the sensitivity of the ligand-receptor recognition by a factor as large as 50. We have demonstrated the utility of our method using streptavidin as the model receptor and biotinylated RNase A as the model ligand. We have also applied our technique to a commercially available kit for rheumatoid factor (RF) with successful results. The same method was also successfully applied for the detection of typhoid whose antibodies were purified and attached to polystyrene particles by our collaborators from DRDE Gwalior. In Chapter 5, we have studied the statics and dynamics of colloidal particles at different applied electric fields from zero to beyond the threshold field. We have taken a series of time-lapsed images and calculated out the pair-correlation function, mean squared displacement, structure factor, non-Gaussian parameter etc. We have studied both mono-dispersed colloidal system and binary colloidal system (mixture of two different sizes of particles). The aggregates formed in the two cases were analysed with the help of Voronoi polygons to quantify the microscopic structure. In mono-dispersed system, the aggregates formed were two-dimensional hexagonal crystals and we have used this system to study the freezing transition in 2-dimension. The properties of the system in the liquid and the crystalline state satisfy various criteria for the 2-d freezing transition. The first maximum of the structure factor at the voltage at which freezing occurs, is 5.5 as has been suggested for the 2-d freezing. This is reflected in the dynamics of the system also, where the ratio D/D0 falls below 10%, in accordance with the LPS (L¨owen, Palberg, Simon) criterion for freezing in 2-d colloidal systems [Phys. Rev. Lett. 70, 1557 (1993)]. However, in the binary colloidal system the clusters formed were not crystalline but more like 2-d dense liquids. A closer inspection of these clusters reveals that the motion of a smaller subset of particles is cooperative and follows string-like paths. The mean square displacement of such a system shows a plateau in the intermediate times which indicates the “caging” of particles by its neighbours. A peak in non-gaussian parameter indicates the presence of dynamical heterogeneities in the system. In Chapter 6, we have described the use of multiple particle tracking to study the microrheology of semidilute solutions of wormlike micelles and compared the results with those from macrorheology experiments done on the same samples. Two concentrations of CTAT (1.3% and 2%) were used. We observed that, in spite of the mesh size being much smaller than the size of the probe particles, the viscoelastic response function calculated using the one-point microrheology does not match with that measured from macrorheology. This can be attributed to the fact that there is another important length scale in the system, the mean micellar length, and it is comparable to the probe particle size. Two-point microrheology was successful in verifying the macrorheology results for CTAT 1.3% but it fails to do so for CTAT 2%. We attribute this to the fact that in a higher viscosity sample (2%), the hydrodynamic force propagate to a lesser distance, thereby limiting the measurable correlation between the particles and precluding the success of two-point microrheology. Chapter 7 describes a rheological study of aqueous solutions of varying concentration of cationic cetyltrimethyl ammonium bromide (CTAB) and anionic sodium-3-hydroxynapthalene-2-carboxylate (SHNC) kept at a fixed molar concentration ratio [CTAB]/[SHNC] = 2. At this molar ratio, the surfactants self-assemble into wormlike micelles which get entangled above the overlap concentration to form viscoelastic gel. The range of the total surfactant concentration φ varies from 1.17% to 5.16% by weight. We found that, plateau modulus, G0, shows a power law dependence on the surfactant concentration, φ, with an exponent 3, which is higher than the expected value of 2.25 observed for the one-component wormlike micelles. Zero shear viscosity, η0, and relaxation time, τR show a maximum at the surfactant concentration, φmax = 1.9% in contrast to a monotonic increase with φ. We propose that this non-monotonic behaviour is due to the unusual dependence of the average micellar length L ¯on φ, showing a maximum in average micellar length L at φmax. This argument provides a strong support to the model of micellar growth in the presence of electrostatic interactions developed by Mackintosh et. al [Europhys. Lett. 12, 697 (1990)]. The presence of electrostatic interactions also appears in the behaviour of the plateau modulus G0 that exhibits a larger φ dependence than in highly screened micelles. In the non-linear flow experiments, a minimum observed in critical shear rate (the shear rate at which shear thinning starts), ˙γc, at φmax strengthens our arguments. In Chapter 8, we describe the phase behaviour and rheology of SDS+PTHC (sodium dodecyl sulphate + p-toluidine hydrochloride) micellar solutions at different molar ratios α=[PTHC]/[SDS]) of the two components. At low values of α, polarizing microscopy observations reveal a transition from an isotropic to a nematic phase of disk-like micelles, whereas a transition to a lamellar phase occurs at higher α values > 0.5, on increasing the surfactant content. Linear rheology of the isotropic micellar solution reveal a viscous behaviour over a large range of surfactant concentrations. Surprisingly, this also extends to the nematic phase of disk-like micelles observed at α =0.2 and φ =0.35. These systems also exhibit a viscoelastic behaviour over a narrow range of surfactant concentration as reported in earlier studies. The extent of the viscoelastic region of the isotropic micellar solution also decreases with increase in α. Frequency sweep curves in this region, scaled on to a master curve is reminiscent of dilute suspensions of hard spheres or rigid Brownian rods. Consistent with the results from oscillatory shear measurements, the f;ow behaviour examined under steady shear is Newtonian over a large range of surfactant content in the isotropic micellar solution. An interesting result in these studies is the non-monotonic behaviour of the viscosity with increase in surfactant concentration. It is likely that the sharp rise in viscosity arises from a jamming effect of the rigid rods. Dynamic light scattering studies suggest that the drop in viscosity is due to the decrease in the length of the micellar aggregates. This is followed by a change in the morphology of the micelles from rods to disks as indicated by the transition to a nematic phase of disk-like micelles or a lamellar phase. A change in the morphology of micellar aggregates with increase in α is expected in mixed surfactant systems with strongly binding counterions. However, the surprising result is the change in morphology of the micellar aggregates with surfactant content. Such a behaviour is seen in mixed surfactant systems for the first time. The thesis concludes with a summary of our main results and a brief discussion of the scope of future work in Chapter 9.

Im Grundwasser mobile Feststoff-Partikel stehen im Verdacht, den Transport schwerlöslicher Schadstoffe zu begünstigen. Die Partikel-Konzentration im Wasser lässt sich aber nur mittels einer aufwändigen Probenahme bestimmen. Vor diesem Hintergrund wurden im Rahmen dieser Arbeit Feld- und Laborversuche durchgeführt. In Feldversuchen zur Probenahme wurde festgestellt, dass für eine Stabilisierung der Partikel-Anzahl-Konzentration (CN in Partikel&amp;gt;Nachweisgrenze/L) die Dauer der Probenahme ausschlaggebend ist, nicht das insgesamt geförderte Volumen. Eine hohe Förderrate hat dabei nicht automatisch eine stärkere Mobilisierung von Partikeln aus dem Partikel-Depot im Umfeld der Messstelle zur Folge, wie es häufig postuliert wird. Die Gewinnung einer repräsentativen Partikelprobe macht eine Probenahme-Dauer von mindestens 5, häufig sogar über 10 oder 12 Stunden erforderlich. Empfehlungen zur Probenahme wurden erarbeitet. Es wurde aber festgestellt, dass sich stabilisierte Werte für CN als Funktion der Förderdauer (t in min) nach CN = a ? t^(-½) ungefähr abschätzen lassen, wenn der Parameter a über CN nach ca. 60 Minuten ermittelt wird. Bei Wässern mit Sauerstoff-Konzentrationen über ca. 1 mg/L kann überdies auch die Verteilung der Partikel auf einzelne Größenklassen bereits nach dieser Zeit ermittelt werden; bei sauerstoffärmeren Wässern verändert sie sich später noch. Angesichts einer starken Variation von CN einer Messstelle ist es generell aber nur möglich, eine Größenordnung für die Hintergrundkonzentration anzugeben. Von Messstelle zu Messstelle sind große Unterschiede bei CN festzustellen. Die Konzentration ist dabei nicht eindeutig abhängig von der Lithologie des Grundwasserleiters oder der Zusammensetzung des Grundwassers. Allerdings konnte eine schwache Korrelation mit dem Redox-Potential (Eh in mV) des Wassers gefunden werden (CN = 1,8?10^6?e^( 0,0087?Eh) [Partikel&amp;gt;2,58µm/L]; r² &amp;amp;#8776; 0,46). Hierüber besteht die Möglichkeit, CN eines Grundwassers auch ohne Partikelmessung abzuschätzen. Insgesamt bewegen sich die Partikel-Massen-Konzentrationen (C in mg/L) der beprobten Wässer meist im Bereich von &amp;lt;1 mg/L, öfters sogar &amp;lt;0,1 mg/L, wenn die im Verlaufe von Probenahme und Messung ausgefällten Fe- und Mn-Oxide nicht berücksichtigt werden. Solche Konzentrationen sind vermutlich kaum in der Lage, relevante Mengen selbst sehr hydrophober Schadstoffen aufzunehmen und zu transportieren. Versuche mit Phenanthren ergaben zudem, dass es anscheinend weniger an bereits in Suspension befindliche Partikel sorbiert, sondern vielmehr in sorbiertem oder kristallinen Zustand aus dem Depot erodiert wird. In Laborversuchen wurde weiter gezeigt, dass in natürlichen Sedimenten ein großes Depot mobilisierbarer Partikel vorhanden ist, das Partikel über einen sehr langen Zeitraum kontinuierlich abgeben kann. Durchbruchsversuche ergaben außerdem, dass ein Großteil zugegebener Partikel bei der Passage durch eine Sedimentprobe zurückgehalten und nur sehr allmählich wieder abgegeben wird. Allerdings war auch ein schneller (präferentieller) Durchbruch zu verzeichnen. In Modellrechnungen konnte gezeigt werden, dass sich ein solcher Partikeltransport weder über eine Filterfunktion noch über die Transportgleichung zufrieden stellend berechnen lässt. Daher ist es nötig, einerseits einen bevorzugten Transport und andererseits eine starke Retardation zu berücksichtigen. Letzteres kann am besten über verschiedene Retardationsfaktoren oder ein dynamisches Partikel-Depot mit Anlagerungs- und Ablösungskonstanten geschehen. / Solid particles that are mobile in groundwater are suspected to enhance the transport of hardly soluble contaminants. But particle concentrations in water can only be measured using time-consuming sampling-procedures. On this background field- and laboratory-experiments were conducted in this work. In field experiments on sampling it turned out, that sampling time is crucial for stabilizing particle number-concentration (CN in particles&amp;gt;detection limit/L), not the volume sampled. A high sampling rate does not -as often argued- automatically result into higher mobilization of particles from the particle-depot in the vicinity of the sampling-well. Obtaining a representative particle sample requires a sampling-time of at least 5, often even more than 10 or 12 hours. In this work recommendations on sampling are given. It was noticed that stabilized values of CN can be estimated as function of sampling time (t in min) by CN = A ? t^(-½), if parameter A is calculated using CN after about 60 minutes. In waters having oxygen-concentrations above approximately 1 mg/L even distribution of the particles into size classes can be estimated after this time; in oxygen-poor waters size-distributions stabilized much later. Because of strong variations of CN in a single measuring well it is generally only possible to give the magnitude of the background-particle-concentration. But among several measuring wells CN may differ by several magnitudes. The concentrations do neither definitely depend upon the lithology of the aquifer nor on the groundwater-composition. But a weak correlation to the redox-potential (Eh in mV) can be found (CN = 1.8 ? 10^6 ? e^( 0.0087 ? Eh) [particles&amp;gt;2.58µm/L]; r² &amp;amp;#8776; 0,46). Using this connection it is possible to estimate a magnitude of CN of a groundwater without even measuring particles. Over all particle mass-concentrations (C in mg/L) of all sampled groundwaters were almost always &amp;lt;1 mg/L, often even &amp;lt;0.1 mg/L, at least if iron- and manganese-oxides that precipitated during measurements were ignored. Such particle concentrations are probably hardly capable of adsorbing and carrying relevant amounts of contaminants, even very hydrophobic ones. Experiments using phenanthrene in contaminated sand additionally showed that it is probably hardly adsorbed onto already suspended particles, but mostly eroded from the particle depot in adsorbed or crystalline state. In laboratory experiments it was further shown that there is a huge depot of mobilizable particles in natural sediments that can continually release particles over a very long period of time. Break-through-experiments showed in addition that a large part of particles fed into the system are retained during the passage through a sediment sample and that they are re-released only very slowly. However, there also was a fast (preferential) break-through. In model calculations it could be shown that such a particle transport can neither be sufficiently described by the filter-function nor by the transport equation. Because of that it is necessary to take into consideration a preferential transport on the one hand and a strong retardation on the other. The last one can at the best be described by several retardation-factors or a dynamic particle-depot having constant attachment- and detachment rates.

Suspension flows in varied settings and at different concentrations of particles are studied theoretically using various modeling techniques. Particulate suspension flows are dispersion of particles in a continuous medium and their properties are a consequence of the interplay among hydrodynamic, buoyancy, interparticle and Brownian forces. The applicability of continuum modeling techniques to suspension flows at different particle concentration was assessed by studying systems at different time and length scales. The first two studies involve the use of modeling techniques that are valid in systems where the forces between particles are negligible, which is the case in dilute suspension flows. In the first study, the growth and progradation of deltaic geologic bodies from the sedimentation of particles from dilute turbidity currents is modeled using the shallow water equations or vertically averaged equations of motions coupled with a particle conservation equation. The shallow water model provides a basis for extracting grain size and depositional history information from seismic data. Next, the Navier-Stokes equations of motion and the convection-diffusion equation are used to model suspension flow in a biomedical application involving the flow and reaction of drug laden nanovectors in arteries. Results from this study are then used prescribe the best design parameters for optimal nanovector uptake at the desired sites within an artery. The third study involves the use of macroscopic two phase models to describe concentrated suspension flows where interparticle hydrodynamic forces cannot be neglected. The isotropic form of both the diffusion-flux and the suspension balance models are solved for a buoyant bidisperse pressure-driven flow system. The model predictions are found to compare fairly well with experimental results obtained previously in our laboratory. Finally, the power of discrete type models in connecting macroscopic observations to structural details is demonstrated by studying a system of aggregating colloidal particles via Brownian dynamics. The results from the simulations match experimental shear rheology and also provide a structural explanation for the observed macroscopic behavior of aging. / text

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Η φασματοσκοπία Raman θεωρείται αξιόπιστη μέθοδος χαρακτηρισμού της μοριακής δομής της ύλης. Τελευταία δε καταβάλλεται μεγάλη προσπάθεια να αναδειχθεί και ως μη επεμβατική τεχνική ανίχνευσης ουσιών φαρμακευτικού και βιολογικού ενδιαφέροντος. Επειδή όμως το φαινόμενο Raman είναι ασθενές και τα όρια ανίχνευσης των ουσιών αυτών ιδιαίτερα χαμηλά, η συμβατική φασματοσκοπία Raman ανταποκρίνεται με μεγάλη δυσκολία στις απαιτήσεις μιας μη επεμβατικής τεχνικής. Τα τελευταία χρόνια με την ανακάλυψη της επιφανειακής ενίσχυσης της σκέδασης Raman (Surface Enhanced Raman Scattering) και την ανάπτυξη της ομώνυμης τεχνικής SERS αυξήθηκε η πιθανότητα του φαινομένου κατά τάξεις μεγέθους. Στο πλαίσιο αυτό, έχουν αναφερθεί και μελέτες SERS με ανίχνευση σκέδασης Raman ακόμη και από ένα μόνο μόριο (single molecule detection). Προϋπόθεση όμως ανάπτυξης φαινομένου SERS είναι η γειτνίαση της εξεταζόμενης ουσίας με νανοσωματίδια αργύρου (Ag) ή χρυσού (Au). Τα νανοσωματίδια αυτά χρησιμοποιούνται κυρίως είτε υπό μορφή κολλοειδών διαλυμάτων είτε υπό την μορφή νανοδομημένων επιφανειών. Μια επιπλέον παράμετρος που πρέπει να συνυπολογισθεί ώστε η μέθοδος αυτή να χαρακτηριστεί αναλυτική είναι η δυνατότητα πραγματοποίησης με SERS ποσοτικών μετρήσεων. Στην παρούσα εργασία ως “υπόστρωμα” εμφάνισης του φαινομένου SERS χρησιμοποιήθηκαν κολλοειδή διαλύματα Au και Ag (~2 mL), στα οποία προστίθεντο 25-100 μL διαλύματος της προς ανίχνευσης ουσίας. Η χρησιμοποίηση της γεωμετρίας σκέδασης 90ο, της πλέον ενδεδειγμένης για λήψη φασμάτων Raman από υγρά και κολλοειδή διαλύματα νανομετρικής κλίμακας (10-100 nm), έδωσε τη δυνατότητα ανίχνευσης συγκεντρώσεων ουσιών-στόχων ακόμη και της τάξης των fg/mL. Επιπλέον, η χρησιμοποίηση μιας κυψελίδας με συνεχή ταλάντωση σε κάθετη ως προς το επίπεδο σκέδασης διεύθυνση (oscillating or shaking cell), επέτρεψε την πραγματοποίηση ποσοτικών μετρήσεων SERS σε συγκεντρώσεις της τάξης των (sub)-ng & (sub)-pg/mL. Η διάταξη αυτή φωταψίας δείγματος και συλλογής σκεδαζόμενης ακτινοβολίας εφαρμόστηκε σε αντικαρκινικά φάρμακα (Novantrone® & Doxorubicin), αντιβιοτικό (Ciproxin®) και βάσεις του DNA. Στην περίπτωση του αντιβιοτικού με ενεργή ουσία το Ciprofloxacin ελήφθησαν ποσοτικά αποτελέσματα σε διαλύματα τεχνητών δακρύων της τάξης των ng/mL, κάτω από την συνολική κλίμακα της μέσης ανασταλτικής πυκνότητας (minimum inhibitory concentration range) του φαρμάκου. Στόχος και φιλοδοξία είναι η τεχνική αυτή να αναδειχθεί ως μια ταχεία μη επεμβατική αναλυτική μέθοδος μέτρησης φαρμακευτικών ή/και βιολογικών ουσιών σε σωματικά υγρά (π.χ. σίελος, δάκρυα, …), για την μελέτη της φαρμακοκινητικής, την έγκαιρη διάγνωση ασθενειών καθώς και τη μελέτη ελεγχόμενης αποδέσμευσης ενεργών ουσιών από πολυμερικές μήτρες σε πολύ μικρές συγκεντρώσεις. Επιπλέον, έγινε προσπάθεια μελέτης/ανίχνευσης μορίων Ε18 primary rat cortical cells με την χρήση του SERS σε συνθήκες προσομοίωσης ηλεκτροχημικού εμφυτεύματος. Για τον λόγο αυτό σχεδιάστηκε και αναπτύχθηκε ένας μικρο-επωαστής (micro-incubator) που επιτρέπει αφ’ ενός μεν τη συντήρηση των κυττάρων σε περιβάλλον κατάλληλο για τη μελέτη τους (layer of Neurobasal-culture medium with a 95% air & 5% CO2 gas flow at 37oC), αφ’ ετέρου δε την προσαρμογή του σε χώρο υποδοχής δείγματος ενός φασματοφωτόμετρου μικρο-Raman για τη λήψη φασματοηλεκτροχημικών μετρήσεων Raman/SERS. Το κύριο σημείο ενδιαφέροντος στο οποίο εστιάσαμε στην παρούσα εργασία αναφέρεται στην διερεύνηση ανίχνευσης βασικών/θεμελιωδών μορίων των κυττάρων στo θρεπτικό υγρό του πειράματος για την ταχεία εκτίμηση ενδεχόμενης αποδέσμευσης DNA που θα αντικατόπτριζε την κατάσταση των κυττάρων. / Laser Raman spectroscopy plays an increasing important role in polymer science, biophysics/biochemistry and life science. Based on vibrational transitions, it has long been regarded as a valuable non destructive tool for the identification of chemical and biological samples as well as the elucidation of molecular structure, surface processes and interface reactions. Spontaneous Raman scattering is however an inherently weak process characterized by extremely small cross sections. Even so, the Raman signal can be highly enhanced when the analyte is placed on or near either to nano-rough noble-metal substrates or to nano-structured colloidal clusters of noble metals. This nano-enhanced scattering process is known as Surface Enhanced Raman Scattering, SERS. With SERS, extremely small amounts of substances can be detected; even single molecule detection has been reported. This constitutes a challenge of applying SERS to extremely low concentration measurements. Nevertheless, the quantitative evaluation by means of SERS was proved difficult, due largely to lack of nano-sized noble metal structures with analytically suitable stability and reproducibility. The commonly used SERS substrates are nanostructured colloids or roughened surfaces of mainly silver and gold undergoing visible or NIR excitation. A note is made of the fact that the Raman scattering geometry that is actually largely used is the backscattering geometry. For solids this is better achieved via a microscope objective, while for liquids via a macro lens. However, the best scattering geometry for Raman light collection from liquids and nanostructured colloids is the right angle scattering; that is, the scattered light is collected at 90o from the excitation light. Having all above in mind, in order to perform quantitative SERS measurements we have designed and developed an oscillating cell making use of the right angle Raman scattering geometry. Originally, the development of the oscillating or “shaking” cell allows large sample sectional surface monitoring, better mixing and homogeneity giving rise to SERS signal reproducibility. In addition, the application of the advantageous for nanocolloidal solutions right angle Raman scattering collection geometry enables SERS measurements at extremely low concentrations. We demonstrated the use this new surface enhanced Raman scattering excitation/collection configuration to monitor the level of the antitumor drugs mitoxantrone and doxorubicin as well as the antibiotic ciprofloxacin at very low concentrations performing fast SERS & SERRS measurements. We have also quantified the concentration of the active agents in aqueous solutions as well as in artificial tears by a partial least-squares (PLS) chemo metric regression algorithm. All above reveal the potential of this technique in the monitoring of the controlled release of active agents from polymeric matrices as well as in the quantitative analysis of drugs in corporal fluids. The only need is to add in a test tube containing 0.5 mL of a nanocolloidal noble metal solution3 about 25-100 μL of a sampling fluid. Finally, in an attempt to detect “living” cells by SERS, to identify DNA components released in a cell culture medium as a “touch mark” of cell death and to perform even single molecule detection, a home-made micro-incubator was designed to allow Raman measurements of neuron cells under the microscope. Commercial micro incubators feature higher optical path between coverslips than the required (<1-1,5 cm) for typical micro-Raman systems even bearing long working distance objectives. It was at that sense a prerequisite to design, construct and optimize a micro-incubator to fit a conventional micro-Raman configuration. The designed micro-incubator meets well-defined stable conditions (temperature, culture solution and atmosphere).

The work presented in this doctoral thesis employs colloidal suspensions to explore key open problems in condensed matter physics. Colloidal suspensions, along with gels, polymers, emulsions and liquid crystals belong to a family of materials that are collectively labelled as soft matter. Compositionally, colloidal suspensions consist of particles whose size ranges from a few nanometers to a few microns, dispersed in a solvent. A hallmark feature of these systems is that they exhibit Brownian motion, which makes them suitable for investigating statistical mechanical phenomena. Over the last fifteen years or so, colloids have been used extensively as model systems to shed light on a wide array of such phenomena typically observed in atomic systems. The chief reason why colloids are good mimics of atomic systems is their large size and slow dynamics. Unlike atomic systems, the dynamics of colloids can be probed in real time with single-particle resolution, which allows one to establish the link between macroscopic behavior and the microscopic processes that give rise to it. Yet another important feature is that colloidal systems exhibit various phases of matter such as crystals, liquids and glasses, which makes them versatile model systems that can probe a broad class of condensed matter physics problems. The work described in this thesis takes advantage of these lucrative features of colloidal suspensions to gain deeper insights into the physics of glass formation as well as shear-induced anisotropic grain growth in polycrystalline materials. The thesis is organized into two preliminary chapters, four work chapters and a concluding chapter, as follows. Chapter 1 provides an introduction to colloidal suspensions and reviews the chief theo-retical concepts regarding glass formation and grain boundary dynamics that form an integral part of subsequent chapters. Chapter 2 describes the experimental methods used for performing the work presented in the thesis and consists of two parts. The first part describes the protocols followed for synthesizing the size-tunable poly (N-isoprolypacrylamide) (PNIPAm) particles used in our study of shear-induced grain growth. The second part describes the instrumentation and techniques, such as holographic optical tweezers, confocal microscopy, rheology and Bragg diffraction microscopy, used to perform the measurements described in the thesis. Chapter 3 deals with our work on the dynamical facilitation (DF) theory of glass forma-tion. Despite decades of research, it remains to be established whether the transformation of a liquid into a glass is fundamentally thermodynamic or dynamic in origin. While obser-vations of growing length scales are consistent with thermodynamic perspectives, the purely dynamic approach of the DF theory has thus far lacked experimental support. Further, for glass transitions induced by randomly freezing a subset of particles in the liquid phase, theory and simulations support the existence of an underlying thermodynamic phase transi-tion, whereas the DF theory remains unexplored. In Chapter 3, using video microscopy and holographic optical tweezers, we show that dynamical facilitation in a colloidal glass-forming liquid grows with density as well as the fraction of pinned particles. In addition, we observe that heterogeneous dynamics in the form of string-like cooperative motion, which is consid-ered to be consistent with thermodynamic theories, can also emerge naturally within the framework of facilitation. These findings suggest that a deeper understanding of the glass transition necessitates an amalgamation of existing theoretical approaches. In Chapter 4, we further explore the question of whether glass formation is an intrinsi-cally thermodynamic or dynamic phenomenon. A major obstacle in answering this question lies in determining whether relaxation close to the glass transition is dominated by activated hopping, as espoused by various thermodynamic theories, or by the correlated motion of localized excitations, as proposed in the Dynamical Facilitation (DF) approach. In Chapter 4, we surmount this central challenge by developing a scheme based on real space micro-scopic analysis of particle dynamics and applying it to ascertain the relative importance of hopping and facilitation in a colloidal glass-former. By analysing the spatial organization of excitations within cooperatively rearranging regions (CRRs) and examining their parti-tioning into shell-like and core-like regions, we establish the existence of a crossover from a facilitation-dominated regime at low area fractions to a hopping-dominated one close to the glass transition. Remarkably, this crossover coincides with the change in morphology of CRRs predicted by the Random First-Order Transition theory (RFOT), a prominent ther-modynamic framework. Further, we analyse the variation of the concentration of excitations with distance from an amorphous wall and find that the evolution of these concentration profiles with area fraction is consistent with the presence of a crossover in the relaxation mechanism. By identifying regimes dominated by distinct dynamical processes, our study offers microscopic insights into the nature of structural relaxation close to the glass transi-tion. In Chapter 5, we extend our investigation of the glass transition to systems composed of anisotropic particles. The primary motivation for this is to bridge a long-standing di-vide between theories and simulations on one hand, and experiments on molecular liquids on the other. In particular, theories and simulations predominantly focus on simple glass-formers composed of spherical particles interacting via isotropic interactions. Indeed, even the prominent theory of Dynamical Facilitation has not even been formulated to account for anisotropic shapes or interactions. On the other hand, an overwhelming majority of liquids possess considerable anisotropy, both in particle shape as well as interactions. In Chapter 5, we mitigate this situation by developing the DF theory further and applying it to systems with orientational degrees of freedom as well as anisotropic attractive interactions. By analyzing data from experiments on colloidal ellipsoids, we show that facilitation plays a pivotal role in translational as well as orientational relaxation. Further, we demonstrate that the introduction of attractive interactions leads to spatial decoupling of translational and rotational facilitation, which subsequently results in the decoupling of dynamical het-erogeneities. Most strikingly, the DF theory can predict the existence of reentrant glass transitions based on the statistics of localized dynamical events, called excitations, whose duration is substantially smaller than the structural relaxation time. Our findings pave the way for systematically testing the DF approach in complex glass-formers and also establish the significance of facilitation in governing structural relaxation in supercooled liquids. In Chapter 6, we turn our attention away from the glass transition and address the problem of grain growth in sheared polycrystalline materials. The fabrication of functional materials via grain growth engineering implicitly relies on altering the mobilities of grain boundaries (GBs) by applying external fields. While computer simulations have alluded to kinetic roughening as a potential mechanism for modifying GB mobilities, its implications for grain growth have remained largely unexplored owing to difficulties in bridging the disparate length and time scales involved. In Chapter 6, by imaging GB particle dynamics as well as grain network evolution under shear, we present direct evidence for kinetic roughening of GBs and unravel its connection to grain growth in driven colloidal polycrystals. The capillary fluctuation method allows us to quantitatively extract shear-dependent effective mobilities. Remarkably, our experiments reveal that for sufficiently large strains, GBs with normals parallel to shear undergo preferential kinetic roughening resulting in anisotropic enhancement of effective mobilities and hence directional grain growth. Single-particle level analysis shows that the anisotropy in mobility emerges from strain-induced directional enhancement of activated particle hops normal to the GB plane. Finally, in Chapter 7, we present our conclusions and discuss possible future directions.

Made available in DSpace on 2015-05-14T12:14:08Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 1022891 bytes, checksum: c086e09a9f99e06278f85a5575162e2b (MD5) Previous issue date: 2009-11-27 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Geometry, topology and elasticity are found in various branchs of physics and they play important roles in the understanding of many physical phenomena. In this work, we present three diferent systems where we can see such importance. First, a quantum neutral particle, constrained to move on a conical surface, is used as a toy model to explore bound states due to both a inverse squared distance potential and a delta-function potential, which appear naturally in the model due the geometry and topology of the cone. In the second one, we propose a method for probing the effects of curved 3-space by using materials with large coefficients of thermal expansion. Studying their fluctuations can be naturally cast in terms of a nonflat background geometry. In the last one, we determine the elastic-mediated interaction between colloidal nanoparticles adsorbed on the surface of free-standing smectic films. In contrast with the short-range character of the elastic- mediated force between particles adsorbed on smectic films supported by a solid substrate, the effective force acquires a long-range character in free-standing films, thus playing an important role in the formation of self-assembly structures in these systems. / A geometria, topologia e elasticidade estão presentes em vários ramos da física, e desempemham papel fundamental no entendimento de vários fenômenos físicos. Nesse trabalho, apresentamos três sistemas distintos onde podemos ver esse papéis. No primeiro, uma partícula quântica neutra confinada a mover-se em uma superfície cônica é usada como modelo para explorar estados ligados devido a um potencial proporcional ao inverso do quadrado da distância e devido a um potencial tipo delta. Ambos potenciais aparecem naturalmente devido a geometria e topologia do cone. No segundo, propomos um método de sondar os efeitos de um espaço curvo tridimensional usando materiais de grande coeficiente de expansão térmica. Neste caso, os três ingredientes citados acima são importantes para o entendimento do problema. Por fim, determinamos a interação entre nanocolóides adsorvidos na superfície de um filme esmético livremente suspenso. Essa interação é mediada por deformações elásticas no filme esmético; ela é de longo alcance, o que é importante para a formação de estruturas coloidais auto organizadas na superfície de tal filme.