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Hydrogels are water-swellable cross-linked polymeric networks that are capable of incorporating a variety of functionalities and responsivities. The stable colloidal form of a hydrogel is known as a microgel and ranges in size from the nano- to the micrometer scale. Microgels can exhibit similar properties to hydrogels, but the colloidal size of the microgel creates differences in their responsive behavior, such as faster reaction kinetics, as compared to their macrogel counterpart. Microgels have been explored for a broad range of applications, either as individual entities or within large scale assemblies. Although these materials have shown a great deal of utility and versatility, microgels have also demonstrated a great deal of complexity due to the fact that they exhibit both polymeric and colloidal properties. This so-called polymer/colloid duality creates intricacies in characterizing the behavior of these materials, especially when coupled with an oppositely charged component within multilayered assemblies. In this dissertation, work is focused primarily on building a greater fundamental understanding of microgels and their behavior within large scale assemblies. This is done through the development of new characterization techniques or through a direct visualization of the interactions of microgels with their surrounding environment with emphasis on their interaction with an oppositely charged linear polyelectrolyte. From these studies, a more developed fundamental understanding of microgels and their assembly into complex structures is obtained, and these findings will aide in the development of future applications of microgel assemblies.

Orientador: Maria Valnice Boldrin Zanoni / Banca: Vicente Assis Benedetti / Banca: Mauro Bertotti / Banca: Lauro Tatsuo Kubota / Banca: Sergio Antonio Spinola Machado / Resumo: A formação de filmes do poliaminoácido poli-l-lisina, (PLL), foi investigada sobre eletrodo de carbono de duas formas distintas: pela sua imobilização direta na superfície do eletrodo obtido pela deposição de 10 μL de uma alíquota seguido de secagem a 80oC em estufa e com a utilização do agente de ligação cruzada Glutaraldeído. Filmes de PLL sobre eletrodo de carbono pirolítico apresentaram-se suficientemente estáveis para pré-concentração do fármaco antiasmático cromoglicato disódico com máxima interação em valor de pH 4,0. Utilizando-se filmes do poliaminoácido obtido com soluções a 1,0% m/v de PLL foi possível estabelecer uma curva analítica para monitoramento do composto em valores de concentração entre 2,18x10-7 mol L-1 a 3,29x10-6 mol L-1 e limite de detecção de 2,1x10-8 mol L-1. A aplicação do procedimento proposto foi realizada para a determinação da droga em urina humana segundo o método de adições-padrão apresentando índices de recuperação de 99,8%, compatível com valores obtidos em procedimentos espectrofotométricos. O nitroprussiato de sódio pode ser monitorado voltametricamente com filmes de PLL imobilizados na superfície do eletrodo de carbono vítreo com auxílio do agente de ligação cruzada Glutaraldeído. O fármaco é pré-concentrado na superfície modificada e exibe maior amplificação de corrente em valor de pH 4,0. Utilizando as melhores condições analíticas, uma curva de calibração foi obtida no intervalo de concentração de 1,21x10-6 a 2,06x10-5 mol L-1 e limite de determinação igual a 4,62x10-7 mol L-1. A aplicação da metodologia foi conduzida para a determinação de NIPRIDE® em plasma e urina humana apresentando índices de recuperação de 95,0% e 96,2%, concordante com resultados obtidos por ensaios espectrofotométricos. A investigação sobre o comportamento voltamétrico do iodeto de potássio com...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The formation of polyelectrolyte film, poly-l-lysina (PLL), was investigated using carbon electrode in two distinct manners: by direct surface immobilization of the electrode obtained by depositing 10 μL of aliquot followed by heating at 80ºC; and with the use of a cross linking agent, glutaraldehyde. PLL films subjected to pirolitic carbon electrode presented themselves as sufficiently stable for the pre-concentrated anti-asthmatic pharmaceutical disodium cromoglicate with a maximum interaction value of pH 4.0. Using polyelectrolyte films, obtained with solutions of PLL 1.00 %m/v it was possible to establish an analytic curve for monitoring the composition in varying levels of concentration, between 2.18x10-7 mol L-1 - 3.29x10-6 mol L-1 and a detection limit of 2.1x10-8 mol L- 1. The proposed application procedure was realized for drug determination in human urine followed by the method of standard additions presenting indexes of recovery, 99.8%, compatible with values obtained by spectrophotometric procedures. The sodium nitroprusside can be monitored voltammetrically with PLL films, immobilized on the surface of a glassy carbon electrode with the assistance of the bonding agent glutaraldheyde. The pharmaceutical is pre-concentrated on the modified surface and exhibited larger current amplification at pH 4.0. Using the best analytic conditions, the calibration curve was obtained at the concentration interval of 1,21x10-6 to 2,06x10-5 mol L-1, and a determination limit equal to 4,62x10-7 mol L-1. The application of this methodology was used to determine NIPRIDE® in plasma and human urine presenting levels of recovery of 95.0% and 96.2%, which agree with the results achieved by spectrophotometric tests...(Complete abstract, click electronic access below) / Doutor

Detection of DNA by electrochemical impedance spectroscopy (EIS) has been reported by many authors and assays have been developed using lab setups. However, as for most detection assay methods there are issues to address to enable the development for the sensor market: Long time-to-result & high complexity for labelled assays and a lack of sensitivity and reproducibility for label-free assays. This work considers two different approaches to address the issues of time-to-result and assay complexity. The first part presents work on achieving rapid sequence-specific electrochemical detection of DNA hybridisation to complementary DNA on an electrode surface. To accomplish assay sensitivity to low DNA target concentrations, a signal amplification strategy is often necessary. One approach is to couple an enzyme to the hybridised target molecules and to deposit insoluble dyes in the subsequent enzymatic reaction, which enhances sensitivity through an increase in the impedance signal in presence of a redox mediator. The time typically taken for this process (20 – 40 min) precludes the use outside lab setups. Therefore, a protocol for sensitive detection in the presence of redox mediator is demonstrated on a practical timescale required for use in sensor applications. Based on these results a model for the fundamental understanding of the amplification reaction is presented which explains the retention of sensitivity at these enhanced timescales. This also enabled further optimisation of the assay for application in single base pair mismatch detection in biologically relevant sequences. Moreover, direct detection of the precipitate formation is demonstrated which enables real-time measurement of the enzymatic reaction without redox agent addition and with enhanced mismatch discrimination. The second part investigates the possibility to detect DNA non-sequence-specifically by non-Faradaic means. This approach aims at reducing assay complexity by establishing whether it is possible to sense the presence of polymeric DNA in solution by measuring changes in the properties of the electrochemical double layer without DNA surface hybridisation. In a sensor setup this approach could be linked to a polymerase chain reaction (PCR) to discriminate polymer from nucleotide monomer and thereby enable PCR progress to be monitored. In this work the response in the electrochemical double layer at the interface of blocked metal electrodes and solutions containing DNA are studied by means of EIS. Blocking layers were applied to the electrode surface to prevent unspecific adsorption of molecules and ions to the metal surface whilst preserving the sensitivity to detection of changes in the double layer. The characteristics of surface blocking layers on disposable electrodes are studied as they are key to understand the double layer properties at a blocked surface. A number of self-assembled monolayers are compared with respect to their temperature stability and their blocking characteristics at different potentials and ion concentrations. This established the basis to study the effect of the presence of, initially, a model polyelectrolyte and, ultimately, DNA on the double layer. Polyelectrolyte detection is successfully shown for the model polyelectrolyte, polyacrylic acid. DNA detection was more challenging and possible causes for deviation from the polyacrylic acid response are discussed.

This thesis studies strong, completely charged polyelectrolyte brushes. Extensive molecular dynamics simulations are performed on different polyelectrolyte brush systems using local compute servers and massively parallel supercomputers. The full Coulomb interaction of charged monomers, counterions, and salt ions is treated explicitly. The polymer chains are anchored by one of their ends to a uncharged planar surface. The chains are treated under good solvent conditions. Monovalent salt ions (1:1 type) are modelled same as counterions. The studies concentrate on three different brush systems at constant temperature and moderate Coulomb interaction strength (Bjerrum length equal to bond length): <br><br> The first system consists of a single polyelectrolyte brush anchored with varying grafting density to a plane. Results show that chains are extended up to about 2/3 of their contour length. The brush thickness slightly grows with increasing anchoring density. This slight dependence of the brush height on grafting density is in contrast to the well known scaling result for the osmotic brush regime. That is why the result obtained by simulations has stimulated further development of theory as well as new experimental investigations on polyelectrolyte brushes. This observation can be understood on a semi-quantitative level using a simple scaling model that incorporates excluded volume effects in a free-volume formulation where an effective cross section is assigned to the polymer chain from where couterions are excluded. The resulting regime is called nonlinear osmotic brush regime. Recently this regime was also obtained in experiments. <br><br> The second system studied consists of polyelectrolyte brushes with added salt in the nonlinear osmotic regime. Varying salt is an important parameter to tune the structure and properties of polyelectrolytes. Further motivation is due to a theoretical scaling prediction by Pincus for the salt dependence of brush thickness. In the high salt limit (salt concentration much larger than counterion concentration) the brush height is predicted to decrease with increasing external salt, but with a relatively weak power law showing an exponent -1/3. There is some experimental and theoretical work that confirms this prediction, but there are other results that are in contradiction. In such a situation simulations are performed to validate the theoretical prediction. The simulation result shows that brush thickness decreases with added salt, and indeed is in quite good agreement with the scaling prediction by Pincus.<br><br> The relation between buffer concentration and the effective ion strength inside the brush at varying salt concentration is of interest both from theoretical as well as experimental point of view. The simulation result shows that mobile ions (counterions as well as salt) distribute nonhomogeneously inside and outside of the brush. To explain the relation between the internal ion concentration with the buffer concentration a Donnan equilibrium approach is employed. Modifying the Donnan approach by taking into account the self-volume of polyelectrolyte chains as indicated above, the simulation result can be explained using the same effective cross section for the polymer chains. The extended Donnan equilibrium relation represents a interesting theoretical prediction that should be checked by experimental data.<br><br> The third system consist of two interacting polyelectrolyte brushes that are grafted to two parallel surfaces. The interactions between brushes are important, for instance, in stabilization of dispersions against flocculation. In the simulations pressure is evaluated as a function of separation D between the two grafting planes. The pressure behavior shows different regimes for decreasing separation. This behavior is in qualitative agreement with experimental data. At relatively weak compression the pressure behavior obtained in the simulation agrees with a 1/D power law predicted by scaling theory. Beyond that the present study could supply new insight for understanding the interaction between polyelectrolyte brushes. / In dieser Arbeit werden vollständig geladene, starke Polyelektrolytbürsten untersucht. Unter Verwendung lokaler Computeserver und massiv paralleler Supercomputer wurden umfangreiche Molekulardynamik Simulationen von verschiedenen Polyelektrolytbürsten Systemen ausgeführt. Die vollständige Coulomb Wechselwirkung zwischen geladenen Monomeren, Gegen- und Salzionen wird explizit berücksichtigt. Die Polymerketten – in gutem Lösungsmittel simuliert – sind mit einem Ende an einer ungeladenen, planaren Grenzfläche verankert. Monovalente Salzionen (1:1) werden identisch wie Gegenionen modelliert. Simulationen bei konstanter Temperatur und moderater Stärke der Coulomb Wechselwirkung (Bjerrum Länge etwa gleich der Bindungslänge) konzentrieren sich auf drei Systeme:<br><br> 1. Polyelektrolytbürsten ohne Salzionen mit variabler Ankerdichte der Ketten<br> Die Simulationsergebnisse zeigen, dass die Polyelektrolytketten bis zu 2/3 ihrer Konturlänge gestreckt sind, wobei die Bürstenhöhe mit zunehmender Ankerdichte leicht wächst. Diese schwache Abhängigkeit steht im Widerspruch zu theoretischen Ergebnissen, die Unabhängigkeit von der Ankerdichte im so genannten osmotischen Regime vorhersagen. In der Folge haben die Simulationen sowohl weitergehende theoretische Überlegungen als auch neue experimentelle Untersuchungen an Polyelektrolytbürsten stimuliert. Zwischenzeitlich konnte die Beobachtung auf semi-quantitativer Ebene auf der Basis eines einfachen Skalenmodells verstanden werden, welches das Eigenvolumen der Polymerketten im Rahmen einer freien Volumen Näherung berücksichtigt. Dabei wird der Kette ein effektiver Querschnitt zugeordnet, von dem Gegenionen ausgeschlossen sind. Das resultierende Regime, in dem nichtlineare Entropie und Elastizität berücksichtigt sind, wird als nichtlinear osmotisches Regime bezeichnet. In der Zwischenzeit konnte dieses Regime auch experimentell verifiziert werden.<br><br> 2. Polyelektrolytbürsten im nichtlinear osmotischen Regime mit variabler Salzkonzentration <br> Struktur und Eigenschaften von Polyelektrolyten können in einfacher Weise durch Veränderung der Salzkonzentration beeinflusst werden. Nach Pincus sollte für starke Salzkonzentration (groß gegenüber der Konzentration der Gegenionen) die Bürstenhöhe mit wachsender Konzentration abnehmen, jedoch nur als relativ schwaches Potenzgesetz mit einem Exponenten -1/3. In der Literatur sind experimentelle und theoretische Ergebnisse bekannt, die diese theoretische Vorhersage bestätigen – allerdings auch solche, die dazu im Widerspruch stehen. In einer solchen Situation sind Simulationen ein geeignetes Mittel, um theoretische Vorhersagen zu überprüfen: In der Tat bestätigen die vorliegenden Simulationsergebnisse in eindeutiger Weise die theoretische Vorhersage von Pincus.<br><br> Das Verhältnis zwischen Buffer Konzentration und effektiver Ionenstärke in der Polymerschicht ist nicht nur von theoretischem Interesse, sondern hat ebenso experimentelle Relevanz. Die Simulationen zeigen, dass die mobilen Ionen innerhalb und außerhalb der Polyelektrolytbürste inhomogen verteilt sind. Ein Erklärungsversuch mit Hilfe des Donnan Gleichgewichts liefert nur für sehr kleine Salzkon-zentrationen befriedigende Übereinstimmung, ansonst ein qualitativ unterschiedliches Verhalten. Wird jedoch das Eigenvolumen der Ketten in ähnlicher Weise wie oben skizziert berücksichtigt, können die Simulationsdaten bei identischer Parameterwahl in nahezu perfekter Übereinstimmung reproduziert werden. Der erweiterte Ansatz für das Donnan Gleichgewicht in konzentrierten Systemen stellt eine interessante theoretische Vorhersage dar, die auch experimentell überprüft werden sollte.<br><br> 3. Wechselwirkung zwischen zwei Polyelektrolytbürsten ohne Salz <br> Repulsive Wechselwirkungen zwischen Polymerbürsten haben in unterschiedlichen Zusammenhängen eine große Bedeutung, so z.B. bei der Stabilisierung von Dispersionen oder bei der Reduzierung von Reibungswiderständen in biologischen Systemen. In den vorgestellten Simulationen von zwei Polyelektrolytbürsten, die an gegenüberliegende Grenzflächen verankert sind, wird der osmotische Druck in Abhängigkeit vom Abstand D der Ankerflächen untersucht. Mit abnehmendem Abstand werden unterschiedliche Regime im Verhalten des Druckes beobachtet. Dieses Verhalten stimmt qualitativ mit experimentellen Ergebnissen überein. Für relativ schwache Überlappung folgt das Verhalten des Drucks dem theoretisch vorhergesagten 1/D Skalengesetz. Darüber hinaus liefert die Simulationsuntersuchung neue Daten zum Verständnis der Wechselwirkung zwischen Polyelektrolyt Bürsten.

The layer-by-layer assembly (LBL) of polyelectrolytes has been extensively studied for the preparation of ultrathin films due to the versatility of the build-up process. The control of the permeability of these layers is particularly important as there are potential drug delivery applications. Multilayered polyelectrolyte microcapsules are also of great interest due to their possible use as microcontainers. This work will present two methods that can be used as employable drug delivery systems, both of which can encapsulate an active molecule and tune the release properties of the active species. <br><br> Poly-(N-isopropyl acrylamide), (PNIPAM) is known to be a thermo-sensitive polymer that has a Lower Critical Solution Temperature (LCST) around 32oC; above this temperature PNIPAM is insoluble in water and collapses. It is also known that with the addition of salt, the LCST decreases. This work shows Differential Scanning Calorimetry (DSC) and Confocal Laser Scanning Microscopy (CLSM) evidence that the LCST of the PNIPAM can be tuned with salt type and concentration. Microcapsules were used to encapsulate this thermo-sensitive polymer, resulting in a reversible and tunable stimuli- responsive system. The encapsulation of the PNIPAM inside of the capsule was proven with Raman spectroscopy, DSC (bulk LCST measurements), AFM (thickness change), SEM (morphology change) and CLSM (in situ LCST measurement inside of the capsules). The exploitation of the capsules as a microcontainer is advantageous not only because of the protection the capsules give to the active molecules, but also because it facilitates easier transport. <br><br> The second system investigated demonstrates the ability to reduce the permeability of polyelectrolyte multilayer films by the addition of charged wax particles. The incorporation of this hydrophobic coating leads to a reduced water sensitivity particularly after heating, which melts the wax, forming a barrier layer. This conclusion was proven with Neutron Reflectivity by showing the decreased presence of D2O in planar polyelectrolyte films after annealing creating a barrier layer. The permeability of capsules could also be decreased by the addition of a wax layer. This was proved by the increase in recovery time measured by Florescence Recovery After Photobleaching, (FRAP) measurements. <br><br> In general two advanced methods, potentially suitable for drug delivery systems, have been proposed. In both cases, if biocompatible elements are used to fabricate the capsule wall, these systems provide a stable method of encapsulating active molecules. Stable encapsulation coupled with the ability to tune the wall thickness gives the ability to control the release profile of the molecule of interest. / Verkapselung ist ein vielseitiges Werkzeug, das zum Schutz und zum Transport von Molekülen ebenso eingesetzt werden kann, wie zur Verbindung von Reaktionspartnern in einem gemeinsamen, von der Umgebung abgeschirmten Raum. Es basiert auf einem einfachen Vorbild der Natur. Pflanzen schützen ihren Samen zum Beispiel durch eine harte, nahezu undurchdringbare Schale (Nüsse) oder durch eine selektiv durchlässige Hülle, wie bei Weizen, der sobald er feucht wird zu keimen beginnt. Die Natur setzt durch den Einsatz des Hülle-Kern Prinzips sehr effizient die Kontrolle über Durchlässigkeit und Anpassung an bestimmte Aufgaben um. <br><br> Wird das Hülle-Kern-Prinzip zum Schutz oder Transport von Molekülen eingesetzt, so sind die zu verwendenden Kapseln nur wenige Mikrometer groß. Sie werden dann als Mikrokapseln bezeichnet. Zur Erzeugung dieser Mikrokapseln werden verschiedene Methoden verwendet. Der heute übliche Weg geht von einer ca. 5-10 Mikrometer großen Kugel (Kern) aus, die mit einer stabilen und an die gewünschten Eigenschaften angepassten Schicht von wenigen Nanometern versehen wird. Im Anschluss wird der Kern herausgelöst und eine hohle, stabile Kapsel erhalten. <br><br> Schichten von wenigen Nanometern Dicke können aus Polyelektrolyten durch das Layer-by-Layer-Verfahren (LbL) hergestellt werden. Dieses Verfahren eignet sich auf Grund seiner vielen Anpassungsmöglichkeiten besonders zum Aufbau der Schichten für Mikrokapseln, da sich die Eigenschaften der Beschichtung bereits beim Aufbau der Schicht auf die Bedürfnisse maßschneidern lassen. Diese Arbeit befasst sich mit der Erzeugung von Mikrokapseln, deren Eigenschaften temperaturabhängig sind. Dies wurde auf zwei Wegen erreicht. Zum einen wurden Kapseln aus Polyelektrolyten und Wachs aufgebaut. Bei Temperaturerhöhung schmilzt das Wachs und versiegelt die Kapsel. Zum anderen werden Kapseln mit einem Wärme empfindlichen Polymer gefüllt. Bei Temperaturerhöhung kollabiert das Polymergerüst. Der enthaltene Wirkstoff wird freigesetzt.

There has been growing interest in designing and development of suitable micro or nano drug delivery system with the ability to target site specifically and release the payload in a predetermined fashion. Recently a new type of system called polyelectrolyte microcapsules and thin films have been proposed and developed for applications such as, biomedical devices to micro sensing and drug delivery. Owing to its advantages of mild preparation conditions, multifunctionality, with programmable characteristics and to encapsulate large amount of materials, it has shown immense potential. In the present research, multilayer polyelectrolyte thin films composed of Poly(methacrylic acid) (PMA) and Poly (vinyl pyrrolidone) (PVP) were deposited on the flat substrates using layer by layer (LBL) technique. The film growth and its deconstruction under physiological conditions were characterized using UV Visible spectrophotometer and Scanning Electron Microscopy (SEM). Hollow microcapsules composed of PMA and PVP were also produced with the help of sacrificial silica template using the same LBL adsorption technique. After coating the desired number of PVP and PMA layers, the colloidal template was removed with a buffer system composed of Hydrofluoric acid (HF) and Ammonium fluoride (NH4F). The obtained capsules were characterized for its surface morphology using SEM and Atomic Force Microscopy (AFM). The hydrogen bonding in capsule formation was confirmed by Fourier Transform Infrared Spectroscopy (FTIR). Encapsulation and release with the microcapsules was carried out using Rifampicin (Antitubercular drug) as a model drug. The interaction of empty and drug loaded capsules with Mycobacterium Smegmatis cell line was investigated. It was found that the empty capsules did not affect the cell growth indicating their biocompatibility. Confocal microscopy studies with Doxorubicin (anticancer drug), which is a naturally fluorescent molecule, showed the drug is indeed encapsulated inside the hollow capsule. From the above studies, it was concluded that polyelectrolyte capsules have the potential to be used for delivering drugs.

Electrostatic self-assembly is a simple, yet versatile and environmentally friendly technique. This technique has been widely used in different areas and recently it has also been used to make nano-structured separating layers for composite polyelectrolyte pervaporation membranes. Non-porous substrates are usually employed for electrostatic self-assembly depositions, but porous substrates have to be used for membrane applications because the composite membranes fabricated with non-porous substrates will have low permeation fluxes. When porous substrates were used to make composite membranes for pervaporation, it was reported that 60 double-layers were needed to get a membrane with suitable separation performance. The deposition of each double-layer needed about one hour, and the fabrication of reported self-assembled membranes with porous substrates was time-consuming and, from an industrial point of view, not practical. <br /><br /> The aim of this work was to make self-assembled composite membranes in a more practical way. The methodology used here is to find appropriate materials and suitable preparation conditions to make self-assembled composite membranes that have less than 10 self-assembled double layers but still have good performance for the dehydration of isopropyl alcohol (IPA)/ water mixtures by pervaporation. <br /><br /> A hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane is a permanently charged porous material. In this work, this porous material was, for the first time, used as a substrate for the fabrication of a composite self-assembled membrane. It was found that the hydrolyzed porous PAN membranes were good substrates for making self-assembled membranes for pervaporation. <br /><br /> In order to reduce the number of the depositions required for making composite membranes with suitable separation performance, a new deposition technique, concentration-changing deposition technique, has been developed. To obtain more extended conformations of polyelectrolytes to prevent them from going into the pores on a porous substrate, dilute deposition solutions were used for the first several depositions. After these first depositions, the pore size of the porous substrate had been reduced and more concentrated solutions (but still dilute solutions) could be used for the subsequent depositions. By using more concentrated deposition solutions, the number of the polyelectrolyte coils adsorbed by the charged substrate was increased and the thickness of each deposited layer was increased. In this way, the total number of deposition layers needed for a good membrane would be decreased. It has been proved in this work that the number of deposition layers in a composite membrane can be reduced by using the concentration-changing deposition technique. <br /><br /> By selecting appropriate materials and by selecting proper preparation conditions, composite polyelectrolyte membranes with less than 10 self-assembled double layers have been successfully fabricated. The obtained membranes had good performance for the dehydration of IPA/water mixtures by pervaporation. The lowest number of double layers in a composite membrane was 2 and this composite membrane had both a high flux and a high selectivity. It was also found that using polyelectrolytes with high molecular weights and a porous substrate with fine pores were the prerequisites for making composite polyelectrolyte membranes with less than 10 self-assembled double layers, while using a polyelectrolyte pair with high charge densities was the prerequisite for making composite membranes with a high selectivity. The successful fabrication of polyelectrolyte membranes with less than 10 double layers makes self-assembled membranes more practical because self-assembled composite membranes can be easily fabricated. <br /><br /> The data reproducibility and the stability of self-assembled composite membranes with less than 10 double layers have been discussed in this work. Random defects in the self-assembled separating layer and low repeatability of thickness in the first several deposition layers are believed to be the major reasons for the relatively low data reproducibility of single composite membranes, while the conformation change of adsorbed polyelectrolytes is one of the reasons for the flux reduction of composite membranes with less than 10 self-assembled double layers. Though the flux reproducibility of single membranes is barely acceptable (relative error about 25%), the average fluxes of several membranes made under the same conditions show good reproducibility. All composite membranes with less than 10 self-assembled double layers, from a structure point of view, were stable because the fluxes of polyelectrolyte membranes didn?t increase as time passed. <br /><br /> The separation performance of the self-assembled composite membranes developed in this work is not as good as it was originally expected, but it is still better than that of commercial poly(vinyl alcohol) (PVA) membranes for the dehydration of IPA/water mixtures, which indicates that new self-assembled composite membranes could be used for practical dehydration of IPA. The flux of the self-assembled composite membrane with 2 double layers was two times higher than that of reported self-assembled membrane in the literature when an IPA/water feed mixture with 10. 0 wt% of water was used at 60&deg;C. The composite membrane with 2 self-assembled double layers is a high performance membrane for IPA dehydration. <br /><br /> The formation of a single self-assembled layer on a non-porous substrate has been studied, but nothing has been reported about the formation of a self-assembled multilayer on a porous substrate. Based on the separation performance of different self-assembled composite membranes made from different materials and at different fabrication conditions, a two-stage process is proposed to explain the formation of a self-assembled multilayer on a porous substrate. Polyelectrolyte molecules, in the first stage, will deposit on the non-porous portion of the surface of a porous substrate while polyelectrolyte molecules will go into and fill the pores on the surface of a porous substrate to change a porous substrate into a "non-porous" substrate. In the second stage, polyelectrolyte molecules will deposit on a "non-porous substrate" to form a multilayer. This process can also be used to explain the formation of a multilayer on a non-porous substrate.

Electrostatic self-assembly is a simple, yet versatile and environmentally friendly technique. This technique has been widely used in different areas and recently it has also been used to make nano-structured separating layers for composite polyelectrolyte pervaporation membranes. Non-porous substrates are usually employed for electrostatic self-assembly depositions, but porous substrates have to be used for membrane applications because the composite membranes fabricated with non-porous substrates will have low permeation fluxes. When porous substrates were used to make composite membranes for pervaporation, it was reported that 60 double-layers were needed to get a membrane with suitable separation performance. The deposition of each double-layer needed about one hour, and the fabrication of reported self-assembled membranes with porous substrates was time-consuming and, from an industrial point of view, not practical. <br /><br /> The aim of this work was to make self-assembled composite membranes in a more practical way. The methodology used here is to find appropriate materials and suitable preparation conditions to make self-assembled composite membranes that have less than 10 self-assembled double layers but still have good performance for the dehydration of isopropyl alcohol (IPA)/ water mixtures by pervaporation. <br /><br /> A hydrolyzed polyacrylonitrile (PAN) ultrafiltration membrane is a permanently charged porous material. In this work, this porous material was, for the first time, used as a substrate for the fabrication of a composite self-assembled membrane. It was found that the hydrolyzed porous PAN membranes were good substrates for making self-assembled membranes for pervaporation. <br /><br /> In order to reduce the number of the depositions required for making composite membranes with suitable separation performance, a new deposition technique, concentration-changing deposition technique, has been developed. To obtain more extended conformations of polyelectrolytes to prevent them from going into the pores on a porous substrate, dilute deposition solutions were used for the first several depositions. After these first depositions, the pore size of the porous substrate had been reduced and more concentrated solutions (but still dilute solutions) could be used for the subsequent depositions. By using more concentrated deposition solutions, the number of the polyelectrolyte coils adsorbed by the charged substrate was increased and the thickness of each deposited layer was increased. In this way, the total number of deposition layers needed for a good membrane would be decreased. It has been proved in this work that the number of deposition layers in a composite membrane can be reduced by using the concentration-changing deposition technique. <br /><br /> By selecting appropriate materials and by selecting proper preparation conditions, composite polyelectrolyte membranes with less than 10 self-assembled double layers have been successfully fabricated. The obtained membranes had good performance for the dehydration of IPA/water mixtures by pervaporation. The lowest number of double layers in a composite membrane was 2 and this composite membrane had both a high flux and a high selectivity. It was also found that using polyelectrolytes with high molecular weights and a porous substrate with fine pores were the prerequisites for making composite polyelectrolyte membranes with less than 10 self-assembled double layers, while using a polyelectrolyte pair with high charge densities was the prerequisite for making composite membranes with a high selectivity. The successful fabrication of polyelectrolyte membranes with less than 10 double layers makes self-assembled membranes more practical because self-assembled composite membranes can be easily fabricated. <br /><br /> The data reproducibility and the stability of self-assembled composite membranes with less than 10 double layers have been discussed in this work. Random defects in the self-assembled separating layer and low repeatability of thickness in the first several deposition layers are believed to be the major reasons for the relatively low data reproducibility of single composite membranes, while the conformation change of adsorbed polyelectrolytes is one of the reasons for the flux reduction of composite membranes with less than 10 self-assembled double layers. Though the flux reproducibility of single membranes is barely acceptable (relative error about 25%), the average fluxes of several membranes made under the same conditions show good reproducibility. All composite membranes with less than 10 self-assembled double layers, from a structure point of view, were stable because the fluxes of polyelectrolyte membranes didn?t increase as time passed. <br /><br /> The separation performance of the self-assembled composite membranes developed in this work is not as good as it was originally expected, but it is still better than that of commercial poly(vinyl alcohol) (PVA) membranes for the dehydration of IPA/water mixtures, which indicates that new self-assembled composite membranes could be used for practical dehydration of IPA. The flux of the self-assembled composite membrane with 2 double layers was two times higher than that of reported self-assembled membrane in the literature when an IPA/water feed mixture with 10. 0 wt% of water was used at 60&deg;C. The composite membrane with 2 self-assembled double layers is a high performance membrane for IPA dehydration. <br /><br /> The formation of a single self-assembled layer on a non-porous substrate has been studied, but nothing has been reported about the formation of a self-assembled multilayer on a porous substrate. Based on the separation performance of different self-assembled composite membranes made from different materials and at different fabrication conditions, a two-stage process is proposed to explain the formation of a self-assembled multilayer on a porous substrate. Polyelectrolyte molecules, in the first stage, will deposit on the non-porous portion of the surface of a porous substrate while polyelectrolyte molecules will go into and fill the pores on the surface of a porous substrate to change a porous substrate into a "non-porous" substrate. In the second stage, polyelectrolyte molecules will deposit on a "non-porous substrate" to form a multilayer. This process can also be used to explain the formation of a multilayer on a non-porous substrate.

ABSTRACT A water-soluble rigid-rod polyelectrolyte sPBI-PS(Li+) could be doped with LiI and cast as a freestanding film from aqueous solution showing a room-temperature in-plane DC conductivity (s|| ) of 8.3¢®10-3 S/cm. However, the cast film assumed an anisotropic microstructure due to preferential orientation of the rigid-rod backbone leading to an out-of-the plane DC conductivity (s^) which was three orders smaller than those of the s||, and severely limited its applications as a solid polyelectrolyte for thin-film battery. In addition to synthesizing rigid-rod polyelectrolyte sPBI-PS(Li+) for comparison, this study used 2-sulfo-terephthalic acid and isophthalic acid in ratios of 15¡G1, 25¡G1, or 50¡G1 for copolycondensation reaction making the rigid-rod backbone of sPBI-PS(Li+) become articulated. Further reaction with 1,3-propanesultone pendants, the rigid-rod polyelectrolyte was changed into a new water-soluble articulated rigid-rod polyelectrolyte A-sPBI-PS(Li+). Various analyses were applied to ascertain chemical structure, purities, thermal properties and molecular weight of synthesized monomers and polymers. Freestanding films of sPBI-PS(Li+) and A-sPBI-PS(Li+) were cast from aqueous solutions doped with LiI, LiBF4, or LiCF3SO3 for various concentrations up to 5 wt.%. Thin-film room-temperature s|| of sPBI-PS(Li+) could be 3.15&#x00B4;10-3 S/cm, and of A-sPBI-PS(Li+) could be 2.76&#x00B4;10-3 S/cm. X-ray scattering and electron microscopic results suggested that the sPBI-PS(Li+) cast film was in-plane isotropic but out-of-the plane anisotropic, and the A-sPBI-PS(Li+) cast film was three-dimensionally isotropic.