This project aims to discover a new means of overcoming the drawbacks of traditional layer-by-layer dip coating through the use of polyelectrolyte complexes (PECs) and electrophoretic deposition. The layer-by-layer process, by which oppositely charged polyelectrolytes or other charged particle are alternately adsorbed onto a substrate to produce a thin film of precisely controllable thickness, is versatile and simple to implement but suffers from requiring numerous, long deposition steps to produce uniform micron thick films. PECs are small associations of oppositely charged polyelectrolytes that, when mixed in non-stoichiometric ratios, can form charged water- soluble particles. There is much still to be determined about the phase behavior of PECs. However, it has been shown that they can exist over a range of conditions. Electrophoretic deposition is a technique used in many commercial applications for the deposition of charged particles onto a conducting substrate. It has even been shown to enhance the deposition of polyelectrolyte single layers and multilayers. This study examines the phase behavior of PECs made of linear poly(ethyleneimine) (LPEI) and poly(acrylic acid) (PAA). PEC behavior is studied over a pH range of 4.0 to 6.0, with no salt added to the system. This study also reports the results of tests examining how soluble PECs responded to changes in pH and whether solid PECs could be made to dissolve through the addition of different salts. Light scattering is used to examine the particle size distribution and effective diameter of PECs in solution. This information is then used to electrophoretically deposit PECs with 10%, 30%, 70%, and 90% excess LPEI. Stylus profilometry is used to assess the thickness of deposited films. The results showing that PEC layers deposited under an applied voltage were 40% to 400% thicker than PECs deposited with no applied potential.

Thesis (M.S.)--Florida State University, 2003. / Advisor: Dr. Farrukh S. Alvi, Florida State University, FAMU-FSU College of Engineering, Dept. of Mechanical Engineering. Title and description from dissertation home page (Aug. 27, 2004). Includes bibliographical references.

CHARLES UNIVERSITY FACULTY OF PHARMACY IN HRADEC KRÁLOVÉ Department of Pharmaceutical Chemistry and Pharmaceutical Analysis Candidate: Aneta Ptáčková Supervisor: PharmDr. Lukáš Lochman, Ph.D. Title of thesis: Modification of capillary wall by graphene for separation applications Capillary electrophoresis (CE) is a highly efficient separation method. Substances are separated due to their different mobility in an electric field. The CE modes of operation can be modified in different ways, e.g. capillary electrochromatography or micellar electrokinetic capillary chromatography. Modification of the inner wall of the capillary is believed to help improve separation efficiency and selectivity. Graphene is carbon with a hexagonal structure in form of two-dimensional sp2 single-atom-thick sheets. Graphene seems to be a suitable material for separation application due to its excellent properties such as large surface area and affinity to aromatic ring through π-π interactions. Our work is focused on the modification of the capillary wall by graphene. One of the methods of capillary wall modification is the Layer-by-Layer method via layering of differently charged substances bounded by electrostatic forces. Another method is chemical coating employing covalent interactions. Different combinations of polymers...

A variety of functional thin films can be produced using the layer-by-layer assembly technique. In this work, assemblies of anionic clay and cationic polymer were studied with regard to film growth and gas barrier properties. A simple, yet flexible robotic dipping system, for the preparation of these thin films, was built. The robot alternately dips a substrate into aqueous mixtures with rinsing and drying in between. Thin films of sodium montmorillonite clay and cationic polymer were grown and studied on poly(ethylene terephthalate) film or a silicon wafer. After 30 clay polymer bilayers were deposited, the resulting transparent film had an oxygen transmission rate (OTR) below 0.005 cm3/m2/day/atm. This low OTR, which is unprecedented for a clay-filled polymer composite, is believed to be due to a ?brick wall? nanostructure comprised of completely exfoliated clay bricks in polymeric ?mortar?. The growth of polymer and clay assemblies is then shown to be controlled by altering the pH of polyethylenimine (PEI). Growth, oxygen permeability, and mechanical behavior of clay-PEI assemblies were studied as a function of pH in an effort to tailor the behavior of these thin films. Thicker deposition at high pH resulted in reduced oxygen permeability and lower modulus, which highlights the tailorability of this system.

A variety of materials were used to fabricate nanocoatings using layer-by-layer (LbL) assembly to reduce the flammability of cotton fabric. The most effective brominated flame retardants have raised concerns related to their toxicity and environmental impact, which has created a need for alternative flame retardant chemistries and approaches. Polymer nanocomposites typically exhibit reduced mass loss and heat release rates, along with anti-dripping behavior, all of which are believed to be due to the formation of a barrier surface layer. Despite these benefits, the viscosity and modulus of the final polymeric material is often altered, making industrial processing difficult. These challenges inspired the use of LbL assembly to create densely layered nanocomposites in an effort to produce more flame-retardant coatings. Laponite and montmorillonite (MMT) clay were paired with branched poly(ethylenimine) to create thin film assemblies that can be tailored by changing pH and concentration of aqueous deposition mixtures. Both films can be grown linearly as a function of layers deposited, and they contained at least 70 wt percent of clay. When applying these films to cotton fabric, the individual fibers are uniformly coated and the fabric has significant char left after burning. MMT-coated fabric exhibits reduced total heat release, suggesting a protective ceramic surface layer is created. Small molecule, POSS-based LbL thin films were also successfully deposited on cotton fabric. With less than 8 wt percent added to the total fabric weight, more than 12 wt percent char remained after microscale combustion calorimetry. Furthermore, afterglow time was reduced and the fabric weave structure and shape of the individual fibers were highly preserved following vertical flame testing. A silica-like sheath was formed after burning that protected the fibers. Finally, the first intumescent LbL assembly was deposited on cotton fabric. SEM images show significant bubble formation on fibers, coated with a 0.5 wt percent PAAm/1 wt percent PSP coating after burning. In several instances, a direct flame on the fabric was extinguished. The peak HRR and THR of coated fabric has 30 percent and 65 percent reduction, respectively, compared to the uncoated control fabric. These anti-flammable nanocoatings provide a relatively environmentally-friendly alternative for protecting fabrics, such as cotton, and lay the groundwork for rendering many other complex substrates (e.g., foam) flame-retardant without altering their processing and desirable mechanical behavior.

Layer-by-layer (LbL) assembly was used to produce highly conductive thin films with carbon black (CB) and polyelectrolytes. The effects of sonication and pHadjustment of the deposition mixtures on the conductivity and transparency of deposited films were studied. Drying temperature was also evaluated with regard to thin film resistance. Sonication and oven drying at 70oC produced films with the lowest sheet resistance (~ 1500 Ω/sq), which corresponds to a bulk resistivity of 0.2 Ω⋠cm for a 14- bilayer film that is 1.3 μm thick. Increasing the pH of the PAA-stabilized mixture and decreasing the pH of the PEI-stabilized mixture resulted in films with 70% transparency due to thinner deposition from increased polymer charge density. Varying the number of bilayers allows both sheet resistance and optical transparency to be tailored over a broad range. Variation of deposition mixture composition led to further reduction of sheet resistance per bilayer. A 14 bilayer film, made from mixtures of 0.25wt% carbon black in 0.05wt% PAA and plain 0.1wt% PEI, was found to have a sheet resistance of approximately 325 Ω/sq. Bulk resistivity was not improved due to the film being 8 μm thick, but this combination of small thickness and low resistance is an order of magnitude better than carbon black filled composites made via traditional melt or solution processing. Applications for this technology lie in the areas of flexible electronics, electrostatic charge dissipation, and electromagnetic interference shielding.

Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 70-74). Also available via the Internet.

Aerodynamic flow control can improve aerofoil performance by influencing the natural growth of boundary layers, which develop on the surface of vehicles moving in viscous fluids. Many active and passive techniques have been developed to reduce drag and/or increase the lift of aerofoil sections. The work presented in this thesis is concerned with the active excitation of the boundary layer on the suction side of aerofoil sections through momentum transfer via a secondary flow. The secondary flow was achieved by air passing through an air breathing device (ABD) which was implemented in the aerofoil surface. This resulted in an almost tangential and uni-directional fluid interaction. Numerical and experimental work showed a beneficial influence of the secondary flow on the aerodynamic characteristics of the studied aerofoil sections. A Taguchi analysis was initially used to confirm findings from previous work on the use of an ABD on a NACA0012 aerofoil section. The resulting parameter ranking showed general agreement with previous data in that the most important parameters are the gap-size i.e. the length over which the two fluids are in contact and the velocity gradient between the two fluids. However, it also raised questions that required an additional in-depth analysis of the parameters governing the flow control process. Due to the greater importance to the modern aviation industry of the NACA65-415 aerofoil section this particular cambered aerofoil section was used for further investigations. This study highlighted the importance of the velocity gradient between the main and secondary flows as well as the location of interaction of the ABD. In addition the gap-size is also important. Consideration of the power requirements for the ABD indicated that this may limit exploitation of the device. An evolutionary search strategy based on genetic algorithms, was employed to optimize the air breathing geometry. This optimisation produced non-intuitive geometries which revealed the importance of promoting an inner fluid recirculation in the device. Finally experimental data in a closed loop wind-tunnel showed trends which were in general agreement with the numerical predictions. However, the measurements indicated significantly greater enhancements of lift forces than those predicted by thenumerical investigation.

Submitted by DANIELA BRANCO TAVARES MASCAGNI null (danibtmascagni@gmail.com) on 2017-07-19T19:56:50Z No. of bitstreams: 1 TESE final.pdf: 4219528 bytes, checksum: 2e34e6b34687082855e27d79457027bc (MD5) / Approved for entry into archive by Luiz Galeffi (luizgaleffi@gmail.com) on 2017-07-19T20:03:40Z (GMT) No. of bitstreams: 1 mascagni_dbt_dr_bauru.pdf: 4219528 bytes, checksum: 2e34e6b34687082855e27d79457027bc (MD5) / Made available in DSpace on 2017-07-19T20:03:41Z (GMT). No. of bitstreams: 1 mascagni_dbt_dr_bauru.pdf: 4219528 bytes, checksum: 2e34e6b34687082855e27d79457027bc (MD5) Previous issue date: 2017-04-24 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Neste trabalho, foram desenvolvidos biossensores eletroquímicos enzimáticos fabricados com óxido de grafeno reduzido (rGO) e funcionalizado depositados pelas técnicas LbL (Layer-by-Layer) e Langmuir-Blodgett (LB) para a detecção de glicose. Para isso, primeiramente foi sintetizado quimicamente o óxido de grafeno (GO) pela oxidação do grafite, em seguida, o GO foi reduzido para aumentar a sua condutividade elétrica e foi funcionalizado em meio estabilizante contendo cloridrato de poli(dialildimetilamônio), formando o GPDDA, ou poli(4-estireno sulfônico) PSS, formando GPSS. Com isso, foi possível formar dispersões aquosas estáveis das nanofolhas de grafeno, essencial para a fabricação de filmes LbL. Em um primeiro momento, foram fabricados biossensores com filmes LbL contendo GPDDA, GPSS e a enzima glucose oxidase (Gox). O desempenho desses biossensores na detecção de glicose foi avaliado em função do número de bicamadas contendo Gox. O melhor desempenho na detecção de glicose foi apresentado pelo biossensor com o filme LbL com a arquitetura (GPDDA/GPSS)/(GPDDA/GPSS)2. Este biossensor apresentou limite de detecção de 13,4 µmol.L-1, sensibilidade 2,47 μA.cm-2.mmol-1.L e faixa analítica entre 0,04 e 0,95 mmol.L-1. Este biossensor foi eficiente na detecção de glicose na presença de interferentes comumente encontrados em fluidos corporais, alimentos e fármacos. Quando avaliado na detecção de glicose em amostras reais, recuperou 100,8% para uma solução eletrolítica comercial e 88,8% para leite sem lactose. Em um segundo momento, foram fabricados biossensores a partir de filmes LB contendo os mesmos materiais utilizados para fabricar os biossensores com filmes LbL (GPDDA, GPSS e Gox), com a finalidade de comparar os dois métodos de fabricação de filmes no desempenho dos biossensores. O desempenho dos biossensores fabricados com filmes LB foi avaliado em relação à quantidade de monocamadas (GPDDA/GPSS/Gox) depositadas. O melhor desempenho na detecção de glicose entre os biossensores com filme LB foi apresentado pelo biossensor de arquitetura (GPDDA/GPSS/Gox)3. Este biossensor apresentou limite de detecção 0,54 µmol.L-1, sensibilidade de 8,69 μA.cm-2.mmol-1.L e faixa analítica entre 0,0018 e 1,5 mmol.L-1. Também se mostrou eficiente na detecção de glicose na presença de interferentes e na detecção de glicose em amostra real, com recuperação de 101,2 % para o leite sem lactose. A partir dos resultados de desempenho dos biossensores com filme LbL e LB foi possível concluir que a técnica LB promoveu uma maior sinergia entre os nanomateriais, atribuída ao maior ordenamento dos nanomateriais proporcionado pela técnica LB. / In this work, enzymatic electrochemical biosensors fabricated with reduced graphene oxide (rGO) and functionalized deposited by the LbL (Layer-by-Layer) and LangmuirBlodgett (LB) techniques were developed for the detection of glucose. Firstly, to get this, graphene oxide (GO) was chemically synthesized by the oxidation of graphite and after GO was reduced to increase its electrical conductivity and it was functionalized in stabilizing medium containing the poly (diallyl dimethyl ammonium chloride) PDDA, forming the GPDDA, or poly (4-styrene sulphonic) PSS, forming GPSS. Hence, stable aqueous dispersions of graphene nanosheets were formed, essential for the fabrication of LbL films. In a first moment, biosensors with LbL films containing GPDDA, GPSS and the enzyme glucose oxidase (Gox) were fabricated. The performance of these biosensors in the detection of glucose was evaluated as a function of the number of bilayers containing Gox. The best performance in the detection of glucose was presented by the biosensor with the LbL film with the architecture (GPDDA/GPSS)/(GPDDA/GPSS)2. It presented a detection limit of 13.4 μmol.L-1 , sensitivity 2.47 μA.cm-2 .mmol-1 .L and analytical range between 0.04 and 0.95 mmol.L-1 . This biosensor was efficient in detecting glucose in the presence of interferents commonly found in body fluids, foods and drugs. When evaluated in the detection of glucose in real samples, it recovered 100.8% for a commercial electrolytic solution and 88.8% for lactose-free milk. In a second moment, biosensors were fabricated from LB films containing the same materials used to fabricate the biosensors with LbL films (GPDDA, GPSS and Gox), in order to compare the two methods of films deposition in the performance of the biosensors. The performance of biosensors fabricated with LB films was evaluated in relation to the amount of deposited monolayers (GPDDA/GPSS/Gox). The best performance on the detection of glucose among LB film biosensors was presented by the architecture biosensor (GPDDA/GPSS/Gox)3. The detection limit was 0.54 μmol.L-1 , sensitivity of 8.69 μA.cm- 2 .mmol-1 .L and analytical range between 0.0018 and 1.5 mmol.L-1 . This biosensor was also efficient in the detection of glucose in the presence of interferents and in the detection of glucose in a real sample, with a recovery of 101.2% for lactose-free milk A conclusion derived from the performance results of the biosensors with LbL and LB films, may support that LB technique promoted a greater synergy among the nanomaterials, attributed to the best arrangement of nanomaterials provided by LB technique.

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