Advanced dispersants were discovered for the fabrication of homogeneous suspensions of multi-walled carbon nanotubes (MWCNT), graphene, and manganese dioxide (MnO2) in both ethanol and water. Thin films of MWCNT, graphene, MnO2, composite films of MWCNT-MnO2 and MWCNT-graphene were prepared using electrophoretic deposition (EPD) and electrolytic deposition (ELD) methods. The mechanisms of dispersion and deposition were investigated. Cathodic EPD was achieved for MWCNT and graphene using positively charged dispersants. Co-deposition of MWCNT and MnO¬2 was performed using a co-dispersant, which dispersed both MWCNT and MnO2 in ethanol. Composite films were tested for electrochemical supercapacitor (ES) purposes. Pulse ELD was used to deposit porous MnO2 coatings on Ni foam substrates from KMnO4 solutions. Cathodic deposition offered advantages, compared to anodic deposition, because the problems, related to anodic dissolution of metallic substrates, can be avoided. The pulse ON/OFF times had significant influence on the morphology and structure of MnO2 films, which further determined the capacitive performance. The influence of MnO2 film thickness on specific capacitance was investigated. Porous and conductive vanadium nitride (VN) was synthesized using melamine as a reducing agent. To further improve film conductivity and specific surface area, MWCNT were incorporated into VN matrix during synthesis. VN-MWCNT composite electrodes and VN-MWCNT/MnO2-MWCNT asymmetric supercapacitor cells were fabricated and tested. The electrodes and cells exhibited excellent electrochemical capacitive performance with good cyclic stability. The asymmetric supercapacitor device showed a voltage window up to 1.8 V, which was the combination of voltage window of VN-MWCNT (-0.9 V--0 V) and MnO2-MWCNT (0 V--0.9 V). Polypyrrole (PPy) coated MWCNT were synthesized in ethanol with ammonium peroxydisulfate solution as an oxidant. The effects of dopants to PPy morphology and conductivity was investigated. Dopants with electrochemical active groups were selected for the synthesis of PPy nanoparticles, where dopants also contributed to the capacitance of the polymer based materials. Both PPy-MWCNT/PPY-MWCNT symmetric supercapacitors and VN-MWCNT/PPY-MWCNT asymmetric supercapacitors were fabricated and tested, where the voltage windows were 0.9 V for the former and 1.3 V for the later. The increase of voltage window was ascribed to the asymmetric structure and negative voltage window of VN-MWCNT composite. / Thesis / Doctor of Philosophy (PhD)

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Electrochemical supercapacitors (ESs) have attracted great attention due to the advantages of long cycle life, high charge/discharge rate and high power density compared to batteries. Significant improvement in ES performance has been achieved via development of advanced nanostructured materials, such as MnO2 and composite MnO2-MWCNT and PPy-MWCNT electrodes. In this dissertation, advanced dispersants were developed and investigated for the dispersion, surface modification and electrophoretic deposition (EPD) of metal oxides, multiwalled carbon nanotubes (MWCNT) and polypyrrole (PPy) in different solvents. Nature-inspired strategies have been developed for the fabrication of MWCNT films and composites. The outstanding colloidal stability of MWCNT, dispersed using anionic bile acids, allowed the EPD of MWCNT. Composite MnO2-MWCNT films were obtained by anodic EPD on Ni plaque and Ni foam substrates. Good dispersion of MWCNT during Py polymerization was achieved and allowed the formation of PPy coated MWCNT. The film and bulk electrodes, prepared by EPD and slurry impregnation methods, respectively, showed high capacitance and good capacitance retention at high charge-discharge rates. The mechanisms of dispersion and deposition were investigated. Cathodic and anodic EPD of MWCNT, MnO2, Mn3O4 was achieved using positively and negatively charged dispersants. Co-deposition of MWCNT and MnO2 was performed using a co-dispersant, which dispersed both MWCNT and MnO2 in ethanol. Composite films were tested for ES applications. The efficient dispersion was achieved at relatively low dispersant concentrations due to strong adsorption of the dispersants on the particle surface, which involved the polydentate bonding. We found the possibility of efficient dispersion of MWCNT in ethanol using efficient anionic dispersants. The electrostatic assembly method has been developed, which offers the benefit of improved mixing of MnO2 and MWCNT. The use of different anionic and cationic dispersants allowed the fabrication of electrodes with enhanced capacitance and improved capacitance retention at high charge–discharge rates and high active mass loadings. The asymmetric devices, containing positive MnO2–MWCNT and negative AC–CB electrodes showed promising performance in a voltage window of 1.6 V. We proposed another novel concept based on electrostatic heterocoagulation of Mn3O4- MWCNT composites in aqueous environment. In this case, various dispersants were selected for adsorption and dispersion of MWCNT and Mn3O4 and this allowed the formation of stable aqueous suspensions of positively charged MWCNT and negatively charged Mn3O4, which facilitated the formation of advanced composites with improved mixing of the components. Testing results showed promising performance of Mn3O4–MWCNT composites for applications in electrodes of electrochemical supercapacitors. / Thesis / Doctor of Philosophy (PhD)

Cellulose wet adhesives are applied to enhance the wet strength of paper products by binding individual paper fibers together. However, the recycling of the wet strength paper is a challenge as the fibers are hard to re-disperse in water. This project demonstrates new strategies for developing cellulose wet adhesives with controllable degradability, facilitating the recycling of wet strength papers. In this project, regenerated cellulose membranes were used to simulate paper fibers. In adhesion measurements, two wet cellulose membranes were laminated with a thin layer of adhesive (1–30 mg/m2), and the 90-degree wet-peel was used as a measure of cellulose wet adhesion. It was shown that the wet-peel was a simple and reliable method to evaluate the wet adhesives for paper products. Cellulose wet adhesives, in the form of microgels or linear polymers, were synthesized by incorporation of hydrazide, amine or azetidinium functional groups that can form covalent bonds to cellulose surfaces. Two strategies to design degradable adhesives were demonstrated in this project. 1) Reductant-responsive microgel adhesives were created by introducing cleavable disulfide linkages, either in the polymer chains tethering adhesive groups or as the microgel crosslinks. More than 70% reduction in wet adhesion was achieved after exposure to a reductant. 2) Degradable polymer cohesive bonds were used to “switch off” the cellulose wet adhesion. This adhesive was created by introducing labile boronate-dextran complexes to the PVAm adhesive layer between cellulose surfaces. The introduction of this new interaction between PVAm chains enhanced the cellulose wet adhesion. In response to subtle pH changes or the presence of monosaccharides, the wet adhesion decreased by 60%. / Thesis / Doctor of Philosophy (PhD) / Wet strength is important for paper products such as paper towels and paper packaging. In paper manufacturing, cellulose wet adhesives are applied to enhance the strength of wet papers by “gluing” together individual cellulose fibers. However, the recycling of wet strength papers is a challenge because the current adhesives prevent the easy disintegration of waste paper back to a suspension of discrete cellulose fibers. As an important part of the bio-based economy, the next generation of paper products are required to be both strong in water and easy to recycle. This thesis explores new designs for wet-strength adhesives that will facilitate recycling. Both nanoparticles and linear polymers were synthesized in this study as cellulose wet adhesives. Many important properties of wet adhesives were probed, including the size of nanoparticles, the pre-treatment of cellulose surfaces, the dosage of adhesives and the choice of adhesive chemistries. A few types of novel cellulose wet adhesives with controllable degradability were synthesized and evaluated. I demonstrated that the cellulose wet adhesion can be “switched off” in response to subtle pH changes, reducing agents or sugars, showing a promising start for the recycling of wet strength papers.

[pt] A incorporação de óleo em formulações cosméticas apresenta vários desafios, pois diferentes parâmetros podem afetar sua preparação e propriedades. Por exemplo, diversos métodos exigem alto fornecimento de energia ou não são adaptáveis para escalas grandes, principalmente em um contexto de aplicações industriais. Se nanopartículas com uma alta incorporação de óleo forem desejadas, os desafios são ainda maiores. Além disso, é essencial formular com produtos químicos já utilizados em cosméticos ou utilizar aqueles que são biocompatíveis. Uma possível estratégia para contornar esses problemas envolve o uso de poli (óxido de etileno) -poli(óxido de propileno)-poli(óxido de etileno) (EOxPOyEOx), que já são aprovados para formulações cosméticas e farmacêuticas. Sua disponibilidade em diferentes comprimentos de cadeia e proporções de grupos EO/PO permite controlar diversas propriedades, como aumentar a estabilidade em meio aquoso ao aumentar o tamanho da cadeia EO. A presente tese tem como objetivo projetar, obter e caracterizar diferentes coloides usando copolímeros tribloco para absorção de ingredientes hidrofóbicos em formulações aquosas, em quatro estudos diferentes. Empregando métodos de preparo simples, exploramos uma variedade de estruturas coloidais, desde nanopartículas até microcápsulas, com o objetivo de entender como a estrutura do copolímero influencia as propriedades desses sistemas. Esses métodos incluíram desde a formação espontânea de cápsulas por complexação eletroestática até o uso de copolímeros para estabilizar dispersões de cristais líquidos. No primeiro estudo, partículas núcleo-casca foram obtidas por complexação entre nanofibrilas de celulose oxidadas (OCNF) e poli(dialildimetilamônio) (PDADMAC), com copolímeros tribloco promovendo a estabilidade e a carga de óleo. Esse método resultou em partículas estáveis e com alta capacidade de incorporação de óleo, adequadas para a liberação controlada de ingredientes ativos. No segundo estudo, a dispersão de fases lamelares formadas por sulfato de laurila de sódio e álcoois graxos em copolímeros tribloco permitiu obter nanopartículas com viscosidade ajustável e boa estabilidade, adequadas para produtos com texturas leves. O terceiro estudo utilizou complexação entre surfactantes e polímeros de cargas opostas para formar nanopartículas com alta capacidade de carga de óleo, onde o copolímero tribloco aumentou a estabilidade e a eficiência de carga. Finalmente, o quarto estudo explorou o uso de betaína cocamidopropil como surfactante, formando micelas que podem ser utilizadas em formulações de cuidados pessoais. Os resultados destacam o potencial desses sistemas para aplicações em produtos cosméticos, onde a estabilidade e a incorporação de ingredientes ativos são essenciais. / [en] Oil loading in aqueous formulations is a constant challenge when developing cosmetics with new claims, and different parameters may affect their preparation and properties. For instance, several methods require high energy input or are not adaptable to large-scale production in an industrial context. If nanoparticles with a high amount of oil loading are desired, this becomes even more challenging. Formulating with chemicals already used in cosmetics or using biocompatible ones is also essential. A possible strategy to avoid these issues involves using poly(ethylene oxide)-poly(propylene oxide)- poly(ethylene oxide) (EOxPOyEOx), which are already approved for cosmetics and pharmaceutical formulations, their availability in different chain lengths and proportions of EO/PO groups can allow the control of different properties, such as enhancing stability in an aqueous medium by increasing the EO chain length. This thesis aims to design, obtain, and characterize different colloids, in four different papers, using triblock copolymers to uptake hydrophobic ingredients in aqueous formulations. By employing simple preparation methods, we explore a range of colloidal structures, from nanoparticles to microcapsules, aiming to understand how the copolymer’s structure influences the final properties. These methods included spontaneous capsule formation through charge-driven complexation to the use of copolymers to stabilize liquid crystals dispersions. In the first study, core-shell particles were obtained through complexation between oxidized cellulose nanofibrils (OCNF) and poly(diallyldimethylammonium chloride) (PDADMAC), with triblock copolymers enhancing stability and oil loading. This method resulted in stable particles with high oil incorporation capacity, suitable for controlled release of active ingredients. In the second study, dispersing lamellar phases formed by sodium lauryl sulfate (SDS) and fatty alcohols using triblock copolymers enabled the formation of nanoparticles with water like viscosity and high stability, suitable for products with light textures. The third study utilized complexation between oppositely charged surfactants and polymers to form nanoparticles with high oil loading capacity, where the triblock copolymer improved stability and loading efficiency. Finally, the fourth study explored the use of cocamidopropyl betaine as a surfactant, forming micelles that can be used in personal care formulations. The results highlight the potential of these systems for applications in cosmetic products, where stability and active ingredient incorporation are essential.

Hydrophobic interaction plays an important role in biology, daily lives, and a variety of industrial processes such as flotation. While the mechanisms of hydrophobic interactions at molecular scale, as in self-assembly and micellization, is relatively well understood, the mechanisms of macroscopic hydrophobic interactions have been controversial. It is, therefore, the objective of the present work to study the mechanisms of interactions between macroscopic hydrophobic surfaces in H-bonding liquids, including water, ethanol, and water-ethanol mixtures. The first part of the present study involves the measurement of the hydrophobic forces in the thin liquid films (TLFs) confined between two identical hydrophobic surfaces of contact angle 95.3o using an atomic force microscope (AFM). The measurements are conducted in pure water, pure ethanol, and ethanol-water mixtures of varying mole fractions. The results show that strong attractive forces, not considered in the classical DLVO theory, are present in the colloid films formed with all of the H-bonding liquids tested. When an H-bonding liquid is confined between two hydrophobic surfaces, the vicinal liquid molecules form clusters in the TLFs and give rise to an attractive force. The cluster formation is a way to minimize free energy for the molecules denied of H-bonding with the substrates. Thus, solvophobic forces are the result of the antipathy between the CH2- and CH3-coated surface and H-bonding liquid confined in the film. A thermodynamic analysis of the solvophobic forces measured at different temperatures support this mechanism, in which solvophobic interactions entail decreases in the excess film enthalpy and entropy. The former represents the energy gained by building clusters, while the latter represents loss of entropy due to structure building. Thus, hydrophobic interaction may be a subset of solvophobic interaction. The solvophobic forces are strongest in pure water and pure ethanol, and decrease when one is added to the other. Adding a very small amount of ethanol to water sharply reduced the solvophobic force due to the adsorption of the former with an inverse orientation. An exposure of the OH-group toward the aqueous phase decreases the antipathy between the surface and H-bonding liquid and hence causes the hydrophobic (or solvophobic) forces to decrease. The second part of the study involves the measurement of the hydrophobic forces in the wetting films of water using the force apparatus for deformable surfaces (FADS). This new instrument recently developed at Virginia Tech is designed to monitor the deformation of bubbles to determine the surface forces in wetting films. In effect, an air bubble is used a force sensor. The measurements have been conducted with gold, chalcopyrite, and galena as substrates. The results obtained with all three minerals show that hydrophobic force increases with increasing water contact angle, suggesting that hydrophobic forces are inherent properties of hydrophobic surfaces rather than created from artifacts such as preexisting nanobubbles and/or cavitation. A utility of the intrinsic relationship between hydrophobic force and contact angle is to predict flotation kinetics from the hydrophobicity of the minerals of interest. / Ph. D.

No / Make it connected! 2D close-packed layers of inorganic nanoparticles are interconnected by organic fibrils of oleic acid as clearly visualized by electron holography. These fibrils can be mineralised by PbS to transform an organic-inorganic framework to a completely interconnected inorganic semiconducting 2D array.