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Polymers --- Polyelectrolytes

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This PhD dissertation focuses on gathering more insights in fundamental aspects related to high-speed, small volume dosing of complex fluids, as encountered during the filling of mono-dose pouches of highly concentrated detergent. In such a dosing process, two characteristic flows are observed: shear flow in the tubing and nozzle, and a surface tension driven extensional flows leading to jet break-up. Compared to a regular bottle-filling process, the shear rates and shear stress in the nozzle are more than an order of magnitude larger, and the break-up needs to happen within only fractions of a second. This leads to significant scientific challenges in processing and product formulation, which form the starting point of this PhD dissertation. Following the division of the dosing process in two distinctly different flows this PhD dissertation is likewise split in two parts.The first part of this thesis looks into the surface tension driven, capillary break-up of liquid filaments, in case of fast break-up. High-speed and high-resolution imaging is used to visualize the fast capillary thinning process and subsequently the images are analyzed to extract valuable information. Although image processing algorithms are already available inhouse to detect the filament and its minimal radius, in this dissertation the effort is made to extend the capabilities of the existing algorithms, to allow a more thorough analysis of fast-breaking fluids. The developed analysis routines combine pixel and subpixel accuracy edge detection algorithms, Canny edge detection and Laplacian of Gaussian respectively, to obtain a robust filament shape analysis while maintaining the subpixel accuracy, even in presence of sharp corners and heterogeneities in the fluid filament. Furthermore routines are developed to process jetting images with a significant reduction of noise on the data. At last, a protocol is developed to determine the axial velocity profile in a thinning filament, allowing to perform a local Reynolds number analysis, as well as self-similar scaling. The improved image analysis toolbox subsequently has been used to perform an in-depth investigation of two scientific challenges for which the capillary thinning behaviour is not completely understood.A first scientific challenge aims at finding the origin behind the particle induced accelerated break-up. More specifically, individual particles are observed to accelerate break-up through an active stretching in the filament, making it a potential mechanism to accelerate break-up in dosing processes. With well-thought experiments, an ideal case in which a single particle induces the accelerated thinning, is created and analyzed, allowing us to explain the origin of the active stretching force. Indeed, a force-balance on this so-called bead-on-a-viscous-string geometry explains that the subtle balance between line tension and viscous stresses in the filament above and below the central bead cause the active stretching force and hence the accelerated thinning.The second scientific challenge consists of the analysis of capillary break-up of otherwise fast-breaking liquids in case of modified thinning conditions, i.e. the presence of a outer immiscible liquid. The outer immiscible liquid reduces the surface tension and slows down the capillary break-up, thereby allowing to investigate liquids that show fast break-up when thinning in air. However, this rather new liquid-liquid approach still lacks a solid basis regarding the exact effect of the outer fluid. Hence, in this part a wide range of liquid viscosities and viscosity ratios is investigated to map out the liquid-liquid capillary break-up behaviour. Using the newly developed image analysis tools combined with simulations and an determination of the dominating stresses in both fluids, two distinct scenarios can be distinguished. For low viscosity ratios initially the outer fluid dominates the thinning and leads to a parabolic instead of an unidirectional flow field in the inner fluid. While passing through two transitional linear regimes after the initial exponential growth regime, eventually the self-similar, universal, two-fluid Stokes regime is reached. For large viscosity ratios, the flow inside the filament is initially not influenced by the outer fluid, leading to a self-similar viscous thinning after the initial exponential thinning. However, at a critical point the outer fluid begins to affect the flow inside the filament and transitions via a transient linear regime towards the self-similar two-fluid Stokes regime. At last, taking a deeper look into the initial exponential stage, the magnitude of imposed disturbance to create the unstable liquid filament as well as the viscosity ratio are observed to have a direct effect on the exponential growth rate.The behaviour under flow for these suspensions of long rod-like or fiber-like HCO crystals is investigated with different rheological protocols. The HCO suspensions are observed to show a remarkable negative shear stress after intermediate shear rates, a strong elastic recoil, and negative normal stresses during flow. The power-law dependence of plateau modulus and critical strain indicate that the HCO network responsible for this behaviour is in a transient regime in which the interfloc and the intrafloc strength are of the same order of magnitude, as confirmed by confocal laser scanning microscopy images. With wide angle X-ray scattering it was made possible to observe that the crystals can partially orient when subject to intermediate shear rates. Altogether, this lead to the conclusion that the HCO crystal suspension thus forms an open microstructural network with comparable strength of interfloc and intrafloc links, composed of high aspect ratio particles that are able to partially orient under flow allowing to maintain a stress-bearing chain in the sample spanning network even after intermediate shear rates. However, in a high-speed dosing process these shear rates are largely exceeded, and network breakdown is expected to be irreversible.

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This thesis investigates the incorporation of the biopolymer pullulan (PUL), both in regular powder form and as elongated particles, in a capsular device in order to enhance drug delivery. The drug release of PUL powder in a matrix of ethyl cellulose and a plasticizer was compared to previous works with KIR particles. Bad dispersion as well as degradation ocurred during micro-injection molding of the PUL powder mixture, which hindered the desired enhanced drug release with respect to the one of KIR. Thermal analysis and extrusion with rheological measurements was executed to analyze the aforementioned problems and possible solutions are suggested. Next a rheological characterization was carried out on different concentrations of PUL water solutions in view of continuous fibre production via electrospinning, in particular examining the viscoelastic behaviour of the solutions. The solution with highest concentration and molecular weight proved to be most suitable for electrospinning. Indeed, uniform and defect free fibres were obtained from this solution. When making a large amount of fibres, their high surface to volume ratio disrupted the separation process because of too large adhesion of the fibres. Division of the fibre mats was ineffectively tried with an ultrasounds and ball milling. To avoid this difficult separation, creation of short fibres seemed to be a solution. For this reason sprayspinning was implemented, however solvent evaporation was not sufficient, as still a lot of water droplets were obtained. Use of an environmental controlled chamber is proposed as a solution. To cope with these issues, it was decided to mechanically reduce the electrospun fibre mats to small flake-like structures. Due to time reasons, it was not possible to test the effectiveness of these flakes of nanofibres and compare it to the powder form. This part would then be addressed to future works.

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Quantum dots (QDs) are nanometer sized semiconductor materials that are regularly used in modern optical applications like cancer-imaging technologies and high quality displays. A major drawback is the loss of photoluminescence and quantum yield as a result from degradation reactions due to oxygen contact and high temperatures. To withstand oxygen rich environments a high demand for QD protection systems is perceived. The development of a core-shell structure that encapsulates QDs while having a minimal impact on its optical properties is therefore desired. This thesis forms a foundation for the coaxial electrospraying pathway towards core-shell protection particle development. Based on the literature and single nozzle experiments, a material choice was made and effects of parameter changes during electrospraying were studied. A 3 wt.% PMMA/ethylacetate solution is used to form a solid PMMA shell. For the core, a cross-linked 3D network of poly-(LMA-co-EGDMA) was chosen because of the better photothermal stability for QDs in comparison to linear polymers, and ability to create chemical bonds between polymer chains and ligands on the surface of modified QDs. Due to the requirement of the polymerization and cross-linking step, the core solution of LMA and EGDMA monomers was first encapsulated by the PMMA shell during coaxial electrospraying, thus creating a liquid-core/solid-shell of LMA+EGDMA+initiator/PMMA. After that, a thermal initiation reaction was conducted to polymerize the liquid core, avoiding a more conservative UV curing that deactivates the QDs, and resulted in the core-shell structure of poly-(LMA-coEGDMA)/PMMA. Since the electrospraying process depends on a multitude of interrelated parameters, the optimization of this process forms a major challenge. Based on SEM and confocal microscopy analysis on particle sizes and morphologies, the selected optimal conditions were the following: environmental temperature of 30 °C, relative humidity of 45 %, tip-to-collector distance of 17 cm, applied voltage of 18 kV, core flow rate of 0.2 mLh and a shell flow rate of 0.8 mLh. Changes in parameter values have a significant influence on particle shape. Especially with the applied voltage, the environmental parameters and the flow rates, the changes were most influential. Planned core-shell structures were reached and the phenomenon of dye diffusion was witnessed. The influence of polymerization temperature and polymerization time on the thermal properties was analyzed using TGA and DSC. Complete core polymerization was reached by applying a temperature of 65 °C for 90 min, 75 °C for 40 min and 85 °C for 20, 40 and 60 min. DSC curves confirmed the presence of a polymerization reaction for the non-polymerized sample at temperatures evolving towards 100 °C. The degradation temperatures were higher for polymerized core-shell particles (124 - 132 °C) than for non-polymerized core-shell particles (113 °C). Further research with the inclusion of QDs is recommended since both electrospraying and polymerization experiments produce promising results regarding the morphology and thermal stability of the core-shell structure.

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Electrospraying and -spinning is a polymer processing technique with very specific applications in the pharmaceutical, clothing, membrane and biochemical industry. The technique is popular for its good size-control capabilities of the small particles and fibres it produces. The process induces high strain rates, what could possible cause changes in the molecular weight of the sample. This is problematic, because a change in the molecular weight will change the end properties of the produced polymer. This thesis first discusses the effect of concentration and molecular weight of the polymer PEO (polyethylene oxide) dissolved in water on the amount of degradation created during the process. In general, increasing concentration and decreasing molecular weights result in less degradation and for the samples processed with a molecular weight Mv of 0.3·10^6 g/mol indicated that for small chains almost no degradation is taken place. For the largest molecular weights Mv > 4·10^6 g/mol the effect changed and was concluded that an increase in concentration results in more degradation. Afterwards this thesis overviewed three different mechanisms that could instigate this effect. The strain rate and the change in Hencky strain produced similar results. Whenincreasingvaluesaremeasuredintheprocessanincreaseindegradationoccurs, but similar values could result in different amount of degradation between different molecular weights. The last mechanism discussed is the Weissenberg number, for which a change in molecular weight does not effect the ratio of degradation as much, but the method is viewed to have more outlier data.