The phase behavior and phase separation kinetics in polymer solutions in binary mixtures of supercritical carbon dioxide (CO2) and organic solvents were studied for two systems. Solutions of polyethylene (PE) in CO2 + n-pentane were selected as one model system to study both the solid-fluid (S-F) and liquid-liquid (L-L) phase transitions as well as the interplay of these two types of phase separations on the final morphological and thermal properties of PE crystals. Solutions of polysulfone (PSF) in CO2 + tetrahydrofuran (THF) were selected as another model system because of the technological importance of this membrane forming polymer and because of the broad interest in developing new solvent/non-solvent systems for forming microporous materials. These phase boundaries were determined using a high-pressure view-cell and optical techniques over a temperature range of 90-165 oC and pressures up to 55 MPa for PE/n-pentane/CO2 system, and over a temperature range of 25 to 155 oC and pressures up to 70 MPa for PSF/THF/CO2 system. For PE solutions, it has been found that the addition of CO2 to the PE/n-pentane system shifts the L-L phase boundary to significantly higher pressures, but moves the S-F phase boundary only slightly to higher temperatures. The S-F phase boundary which represents the crystallization/melting process in the polymer solution was about 10 oC lower than the crystallization/melting temperatures of the neat polyethylene samples determined by differential scanning calorimetry (DSC). It was further found that the S-F phase boundary in n-pentane displays a unique sensitivity to the pressure-temperature conditions and moves to lower temperatures in the pressure range from 38 to 42 MPa. This effect even though not as augmented remains also for the S-F boundary in the solutions in CO2 + n-pentane mixtures. The miscibility of PSF in THF + CO2 was investigated at CO2 levels up to 14 wt %. This system shows lower critical solution temperature (LCST)-type phase behavior at low CO2 content, which is shifted to upper critical solution temperature (UCST)-type at higher CO2 levels along with an increase in the miscibility pressures. In contrast to the PE system, this system was found to display multiple miscibility windows. A "U"-shaped phase boundary in 92 % THF + 8 % CO2 mixture was observed to transfer to a "W"-shaped phase boundary at 10 wt % CO2, which was further separated into a double "U"-shaped phase boundary at 13 wt % CO2. The specific volume of the polysulfone solutions were found to display a variation parallel to this changing pattern in the phase boundaries, with reduced miscibility being accompanied with an increase in the specific volume. The phase separation kinetics in these two polymer solutions were investigated using time- and angle-resolved light scattering techniques. With the PE solutions, the focus was on the kinetics of S-F phase separation (crystallization) and miscibility and (melting) in n-pentane. Experiments were conducted with relatively dilute solutions at concentrations up to 2.3 wt %. The results show that the crystallization which was induced by cooling at constant pressure is dominated by a nucleation and growth process. In the majority of the experiments the particle growth process was observed to last for about 1 minute with a slight dependence on the crystallization pressure. The phase separation kinetics in PSF solutions were conducted only in a solvent mixture containing 90 wt % THF and 10 wt % CO2. Polymer concentrations were varied up to 3.3 wt %. This system was also observed to undergo phase separation by only nucleation and growth mechanism under these conditions upon reducing the pressure at constant temperature. Several experiments were conducted using a multiple rapid pressure drop technique to identify the depth of the metastable region. PE crystals that were produced by crossing the S-F boundary by different paths were collected and characterized by field emission scanning electron microscopy (FESEM) and DSC. Crystallization was carried out either by cooling at constant pressure, or by cooling without pressure adjustment, or by first crossing the L-L boundary via pressure reduction at a constant temperature followed by cooling. For crystal recovery, the system was depressurized to ambient conditions irrespective of the path. It was found that all of the crystals formed from these solutions show multiple melting peaks in their first DSC heating scans, which however collapse into one crystallization peak in the cooling scans and one melting peak in the second heating scans. The temperatures corresponding to the multiple melting peaks were lower than the single melting temperature of the original PE sample and the melting temperature observed in the second heating scans for all samples. The multiple melting peaks were attributed to the presence of different lamellar thickness that are formed in the crystallization, final depressurization and sample collection stages. Depending upon the crystallization path some differences were noted. The crystals formed by first going through L-L phase separation displayed predominately double melting peaks in the first DSC scan. It was observed that the overall crystallinity is increased by more than 10 % to about 75 % compared to the crystallinity of the original PE sample, which is about 63 %. FESEM characterization showed that the prevailing morphology is composed of plate-like lamellae that show different level of agglomeration depending on the crystallization conditions. The overall structures of the particles were ellipsoid for crystals formed from dilute solutions. For crystals formed from the 1% PE solution, crystal sizes ranged from 4 mm ´ 10 mm for crystals formed at 14 MPa to 30 mm ´ 45 mm at 45 MPa. The crystals formed from 5 wt % solutions in n-pentane at pressures in the range of 38-54 MPa showed different morphologies with features of shish-kebab like structures which were however absent in crystals formed from n-pentane + CO2 solutions. The crystals that were formed from first crossing the L-L phase boundary followed by cooling showed two distinct particle size ranges that were attributed to crystals formed from the polymer-rich and polymer-lean phases that evolve when the L-L phase boundary is crossed. / Ph. D.

Mixed-matrix hollow fiber membranes are being developed to offer more efficient gas separations applications than what the current technologies allow. Mixed-matrix membranes (MMMs) are membranes in which molecular sieves incorporated in a polymer matrix do separation between gas mixtures based on the molecular size difference and/or adsorption properties of the component gases vis-à-vis the porous structure and the nature of adsorption sites in the molecular sieve. The development of MMMs to deliver on its promises has however been slow. The major challenges encountered in the efficient development of MMMs are associated with some of the paradigm shifts involved in their processing. For instance, mixed-matrix hollow fiber membranes are prepared by a dry-wet jet spinning method. For an efficient large scale processing of hollow fibers the rheology and kinetics of phase separation of the MMM dopes are important control variables in the process design. Therefore, this research thesis aims to study the rheology and phase separation kinetics of mixed-matrix membrane dopes. In research efforts to develop predictive models for the shear rheology of suspensions of zeolite particles in polymer solutions it was found that MFI zeolite suspensions have relative viscosities that dramatically exceed the Krieger-Dougherty predictions for hard sphere suspensions. Our investigations show that the major origin of this discrepancy is the selective absorption of solvent molecules from the suspending polymer solution into the zeolite pores. Consequently, both the viscosity of the polymer solution and the particle contribution to the suspension viscosity are greatly increased. A predictive model for the viscosity of porous zeolite suspensions incorporating a solvent absorption parameter, α, into the Krieger-Dougherty model was developed. We experimentally determined the solvent absorption parameter and our results are in good agreement with the theoretical pore volume of MFI particles. In addition, fundamental studies were conducted with spherical nonporous silica suspensions to elucidate the role of colloidal and hydrodynamic forces on the rheology of mixed-matrix membrane dopes. Also in this thesis, details of a novel microfluidic device that enables measurements of the phase separation kinetics via video-microscopy are presented. Our device provides a well-defined sample geometry and controlled atmosphere for in situ tracking of the phase separation process. We have used this technique to quantify the phase separation kinetics (PSK) of polymer solutions and MMM dopes upon contact with an array of relevant nonsolvent. For the polymer solution, we found that PSK is governed by the micro-rheological and thermodynamic properties of the polymer solution and nonsolvent. For the MMM dopes, we found that the PSK is increased by increased particles surface area as a result of surface diffusion enhancement. In addition, it was found that the dispersed particles alter the thermodynamic quality of the dope based on the hydrophilic and porous nature of suspended particles.

Title: The Study of Dynamic Behaviour and Interactions During the Tempera- ture-Induced Phase Separation in Polymer Solutions Author: Hana Kouřilová Department / Institute: Charles University in Prague, Faculty of Mathemat- ics and Physics, Department of Macromolecular Physics Supervisor of the doctoral thesis: doc. RNDr. Lenka Hanyková, Dr. Abstract: 1 H and 13 C high-resolution NMR spectroscopies were used for the phase separation investigation in three types of polymer solutions: i) poly(N -isopropylmethacrylamide)/D2O/ethanol with or without negatively charged comonomer sodium methacrylate, ii) random copolymers poly(N -isopro- pylmethacrylamide-co-acrylamide) in D2O, D2O/ethanol and D2O/acetone and iii) D2O solutions of polymer mixtures poly(N -isopropylmethacrylamide)/poly(N - vinylcaprolactam). For i) cononsolvency effect and influence of temperature on the phase separation was studied. Differences between mesoglobules formed as a consequence of cononsolvency effect and of temperature were found. While inside the cononsolvency-induced mesoglobules no bound ethanol molecules were detect- ed, in the mesoglobules formed by the effect of temperature ethanol molecules were present. The charge introduced into the polymer chains strenghtens polymer- solvent interactions. For ii) mesoglobules were found to be...

Title: Spectroscopic Study of the Dynamical Behavior and Interactions in Supramolecular and Macromolecular Systems Author: Marek Radecki Department: Department of Macromolecular Physics Supervisor: Doc. RNDr. Lenka Hanyková, Dr., Department of Macromolecular Physics Abstract: In this thesis, the temperature-induced phase transition in liner polymer solutins and hydrogels of semi-interpenetrating (SIPNs) and interpenetrating (IPNs) polymer networks was studied with respect to various composition, network architecture and procedure. Thermoresponsive linear polymers based on poly(vinyl methyl ether) (PVME) in water and with terc-buthyl based additives, IPNs of polyacrylamide (PAAm), poly(N -isopropylacrylamide) (PNIPAm), poly(N - vinylcaprolactam) (PVCL) and IPNs and SIPNs of poly(N,N -diethylacrylamide) (PDEAAm) were investigated by the methods of nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), optical microscopy (OM) and swelling experiments. The effect of polymer concentration and presence of additives on the dynamics during the phase separation as well as interactions between the water and the polymer in aqueous solutions of PVME and PVME/additives were established. The increasing content of hydrophilic PAAm component in SIPNs and IPNs shifts the transition toward...

[pt] Com o objetivo de aumentar a capacidade dos poços petrolíferos, métodos convencionais de recuperação são utilizados, os quais consistem na injeção de água ou gás para a manutenção da pressão do reservatório. A produção do óleo ocorre através do deslocamento do mesmo no espaço poroso, onde a água, fluido deslocante, é injetada para ocupar gradualmente o espaço do óleo, fluido deslocado. Devido aos efeitos capilares e às heterogeneidades do meio poroso, uma parcela de óleo residual acaba ficando retida no reservatório, apresentando baixo fator de recuperação de óleo devido a elevada viscosidade do óleo em relação à viscosidade do fluido injetado e altas tensões interfaciais entre os fluidos. A adição de polímeros à água garante um aumento na sua viscosidade, melhorando a razão de mobilidade água/óleo no meio poroso. Uniformizando a frente de avanço e melhorando a eficiência de varrido devido à melhora no deslocamento do óleo. O presente trabalho analisa o comportamento viscoelástico do polímero, isolando o efeito viscoso e elástico em função das taxas de cisalhamento e extensão, implementado em um modelo de simulação de injeção de polímeros na escala de reservatórios. O efeito das propriedades reológicas da solução polimérica mostram nos resultados de produção uma frente de avanço mais estável e consequentemente uma melhora na taxa de recuperação de óleo quando avaliou-se o comportamento puramente cisalhante. Entretanto uma melhora na taxa de recuperação e na estabilidade da frente de avanço para o comportamento puramente extensional só pode ser observado quando o número de capilaridade foi aumentado consideravelmente. / [en] Aiming to increase the capacity of oil fields, conventional recovery methods are used. These methods consist in the injection of water or gas to maintain the reservoir pressure. The oil production typically takes place by displacing this oil in the porous media, where the displacing fluid (water) is injected to gradually occupy the space of the displaced fluid (oil). Since due to capillary effects and the heterogeneity of the porous media, a residual oil portion ends up trapped in the reservoir. These methods lead to low values of oil recovery factor, which occurs mainly by two factors: high viscosity of the reservoir s oil in relation to the viscosity of the injected fluid and high interfacial tension between the fluids. The addition of polymers to the water ensures an increase in the viscosity of the injected fluid, improving mobility ratio between water and oil in the porous media. Thus, standardizing forward swept and improving the swept efficiency due to improved oil displacement, which reduces the formation of preferential paths in the reservoir, usually called fingers. This paper analyzes the viscoelastic behavior of the polymer, by isolating the viscous and elastic effect in function of its extension and shear rates, implemented in a polymer injection simulation model in a reservoir scale. The effect of the rheological properties of the polymer solution show in the production results a more stable injection front and consequently an oil recovery rate improvement when evaluated as a purely shear behavior. However an improvement in the recovery rate and stability of the injection front for pure extensional behavior can only be observed when the capillary number is increased considerably.

No description available.

Master of Science

[pt] O processo de manufatura de fitas adesivas geralmente envolve uma etapa de retirada dos solventes presentes na solução revestida e formação de uma camada de material semi- sólido sobre um substrato impermeável. Devido a alta espessura de adesivo requerida no produto final e a alta concentração de solventes característica da solução revestida, a secagem se torna, muitas vezes, o gargalo do processo produtivo. Ganhos de produtividade em linhas que podem produzir centenas de milhares de metros quadrados de fita adesiva por mês são importantes para viabilizar incrementos na oferta ou redução dos custos operacionais. Esta dissertação apresenta a análise do processo de secagem de soluções poliméricas revestidas sobre substratos impermeáveis através do desenvolvimento de um modelo matemático para representar os fenômenos de transferência de calor e massa. Também propõe uma metodologia para atingir ganhos de produtividade utilizando um programa computacional especialmente desenvolvido para simulação do processo de secagem. A utilidade da metodologia e da simulação é demostrada por um estudo de caso realizado na manufatura de fitas adesivas da 3M do Brasil. / [en] In the manufacturing process of adhesive tapes usually there is a step where the solvents of solution are evaporated in order to allow the formation of a semisolid layer of material over a suitable substrate. As the final product requires high coating weight and solvent concentration on adhesive solution is high as well, the drying becomes, most of the time, the constraint of the overall process. Productivity increase on machines that can produce hundred of thousands of square meters of adhesive tapes per month can represent additional sale volumes or possibility to reduce operating costs. This dissertation presents the analysis of drying process of polymeric solutions coated over impermeable substrates through the development of a mathematical model to represent the heat and mass transfer. It also proposes a methodology to achieve productivity increases using a computer code specially developed to simulate the drying process. The power of this methodology and of the computer- aided simulation is showed by a case study in the manufacturing department of adhesive tapes at 3M Brazil.

After the advent of nanotechnology, self-assembly has become an active area of research, as it being one of the few efficient methods to generate ensembles of nanostructures. In this thesis, we present studies on two dimensional self-assembly of polymer grafted nanoparticle (PGNPs) and thin film modelling approach to understand the physics involved in the self-assembly mechanism of polymeric nanoparticles. The two dimensional, hierarchical assemblies of PGNPs are created from evaporating solution films spread at the air-water interface using Langmuir-Blodgett technique. A transition in the patterns is observed with increase in concentration which is followed by a remarkable re-entrance of initial patterns with further concentration increment. The pattern is long length scale network type at low and high concentrations whereas it is short length scale distribution of clusters at intermediate concentrations. Clusters are composed of lateral arrangement of individual PGNPs. The characteristics of clusters are tailored by changing various experimental conditions such as molecular weight of the grafted chains, concentration, temperature and evaporation rate. The patterns are unaffected by the transfer surface pressure, suggesting that the self-assembly occurs in the presence of solvent via solution thin film instabilities and the resulting structures of PGNPs are frozen upon complete evaporation. Films of neat polystyrene also exhibit similar morphology and transitions in pattern length scales with initial solution concentration as observed in PGNP films. This confirms that the self-assembly of PGNPs is driven by the intrinsic nature of the grafted polymer chains. Gradient dynamics model is employed to study the stability and dynamics of polymer solution thin films by incorporating Flory Huggins free energy and concentration dependent Hamaker constant. Dispersion curves obtained from linear stability analysis of thin film equations show existence of bimodal instability in the film that corresponds to dewetting and decomposition. Phase diagram spanned by concentration and Flory parameter indicate that the thin film instability transits from dewetting to decomposition and then re-enters to dewetting with increase in concentration of the solution. Using the material parameters of the PGNP thin films for linear stability analysis, experimental observations of bimodal length scale of patterns and re-entrant nature are well explained. Nonlinear simulations which are performed to capture the evolution of patterns in the film show that the decomposition progresses through different pathways depending upon the concentration of the solution. This is explained by analyzing the local variation of spinodal parameter (curvature of the free energy per unit area) in the film. The gradient dynamics model is extended to study the stability and dynamics of evaporating solution thin films. Nonlinear simulations demonstrate that the film undergoes evaporative thinning without any significant growth of dewetting or decomposition instability initially and becomes unstable at a certain intermediate thickness where the spinodal parameter of dewetting or decomposition changes the sign. The rupture of the film (dewetting) or the phase segregation (decomposition) occurs explosively and subsequently evaporation progresses till the film attains chemical equilibrium with the ambient vapour phase. Rate of evaporation significantly affect the intermediate thickness at which the patterns emerge and thereby determines the length scale of initial patterns and instability growth rate. Quasi-steady analysis and nonlinear simulations show that the length scales of patterns of dewetting and decomposition decrease with evaporation rate and exhibit a power law behaviour. Thin films in which the solvent quality drops down with confinement due to evaporation are modelled by assuming a simple functional dependence of Flory parameter on mean film thickness. Quasi-steady analysis demonstrates that the dominating instability of such films switches from dewetting to decomposition and then returns to dewetting with increase in the initial concentration of the solution. We note that even though the functional form of Flory parameter with confinement is not exact, it represents the essential nature of the expected variation. We presume that the phenomenon discussed above is quite generic and may manifest itself in many situations where thin films of colloidal solutions undergo a decrease in the solvent quality due to confinement effects resulting in a competition between spinodal dewetting and decomposition instabilities. This will result in a competition and interplay of the different instability scales and by choosing appropriate control parameters novel self-assembled patterns can be created.

[pt] A injeção de soluções poliméricas tem sido utilizada em muitas aplicações para aumentar a viscosidade da fase aquosa e, por conseguinte, reduzir a elevada razão de mobilidade durante o deslocamento de óleo num meio poroso. Evidências experimentais mostraram também que o comportamento viscoelástico de algumas soluções poliméricas pode contribuir para um melhor deslocamento do óleo na escala de poros, reduzindo assim, a saturação de óleo residual. Este comportamento na escala de poros não é claramente compreendido já que a modelagem de um fluxo viscoelástico de uma solução polimérica em meios porosos é extremamente desafiadora. O comportamento do escoamento em escala macroscópica está diretamente associado com o fluxo extensional dominante através das gargantas e poros que formam o meio poroso. Muitos modelos têm sido desenvolvidos com o objetivo de descrever o efeito extensional observados no fluxo de soluções poliméricas de elevado peso molecular. O modelo desenvolvido neste trabalho baseia-se na relação entre a vazão e a queda de pressão do escoamento de soluções poliméricas através de capilares com garganta que servem como um modelo simples da geometria das gargantas de poro. Um modelo de rede de capilares bidimensional foi desenvolvido para obter os parâmetros macroscópicos do escoamento a partir do entendimento do comportamento microscópico. No modelo monofásico, os resultados apresentam efeitos de diferentes parâmetros reológicos no comportamento macroscópico do escoamento. Para estudar o escoamento bifásico, um modelo de rede dinâmico foi desenvolvido. Os resultados obtidos fornecem uma descrição mais detalhada do processo de deslocamento de óleo pela fase aquosa. / [en] Injection of a polymer solution is used in many applications to increase the viscosity of the water phase and therefore reduce the high mobility ratio during oil displacement in porous media. Experimental evidence has shown that the viscoelastic behavior of some polymer solutions may contribute to a better oil displacement at the pore-level, reducing the residual oil saturation. This pore-level behavior is not clearly understood. Modeling viscoelastic flow of polymeric solutions in porous media is extremely challenging. The macroscopic flow behavior is directly associated with the extensional dominant flow through pore throats that form the porous media. Accurate models should be able to describe the extensional thickening effect observed in the flow of dilute high molecular weight polymer solutions. The model developed in this work is based on the flow rate-pressure drop relationship of polymer solution flow through constricted capillaries that serves as a simple model of the geometry of pore throats. A two-dimensional capillary network model is constructed in order to obtain macroscopic parameters from upscaling of the microscopic behavior. In single-phase flow, results show the effect of different rheological parameters on the macroscopic flow behavior. To study a two-phase flow, a dynamic network model was developed. The results obtained provide a more detailed description of the oil displacement by the water phase.