Polymer/ceramic nanocomposites benefit by combining high permittivities (r) of metal oxide nanoparticles with high dielectric strength and excellent solution-processability of polymeric hosts. Simple mixing of nanoparticles and polymer generally results in poor quality materials due mainly to the agglomeration of nanoparticles and poor miscibility of nanoparticles in host materials. Surface modification of metal oxide nanoparticles with phosphonic acid-based ligands was found to afford a robust surface modification and improve the processablity and the quality of nanocomposites. The use of phosphonic-acid modified barium titanate (BaTiO₃) nanoparticles in dielectric nanocomposites dramatically improved the stability of the nanoparticle dispersion and the quality of the nanocomposites. Surface modification of BaTiO₃ nanoparticles allowed high quality nanocomposite thin films in ferroelectric polymer hosts such as poly(vinylidene fluoride-co-hexafluoropropylene) with large volume fractions (up to 50 vol. %), which exhibited a remarkable combination of a high permittvity (35 at 1 kHz) and a high breakdown strength (210 V/µm) leading to a maximum energy storage density of 6.1 J/cm³. The effect of nanoparticle volume fractions on the dielectric properties of this nanocomposite system was investigated and compared with theoretical models. At high volume fraction of nanoparticles, the porosity of the nanocomposites was found to have important role in the dielectric performance. A combined effective medium theory and finite difference simulation was used to model the dielectric properties of high volume fraction dielectric nanocomposites with porosity. These results provide a guideline to optimize the volume fractions of nanoparticles for maximum energy density. Nanocomposites based on phosphonic acid-modified BaTiO₃ nanoparticles can also be used as printable high permittivity dielectrics in organic electronics. High volume fractions (up to 37 vol. %) of phosphonic acid-modified BaTiO₃ nanoparticles dispersed in cross-linked poly(4-vinylphenol) allowed solution-processable high permittivity thin films with a large capacitance density (~50 nF/cm²) and a low leakage current (10 8 A/cm²) suitable as a gate insulator in organic field-effect transistors (OFETs). Pentacene-based OFETs using these nanocomposites showed a low threshold voltage (< -2.0 V) and a large on/off current ratio (Ion/off 104 ~ 106) due to the high capacitance density and low leakage current of the gate insulator.

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Publics are facing a great challenge of infections from pathogens. Polyethylene terephthalate (PET) is widely used in health-care settings. It is vital to develop effective and regenerable antimicrobial PET. In this study, effective antibacterial modification of PET was achieved by immobilizing N-halamine biocide poly (N-chloroacrylamide) (PCA) onto PET through the formation of a surface interpenetrating network. The successful and uniform immobilization was confirmed by FTIR and XPS. The immobilization is durable to a 72 hours soxhlet extraction. Surface morphology of the fabrics did not significantly change after modification with IP less than 20%. The modified fabric can bring 100% reduction of 10e6 CFU/ml of several clinical important bacteria in 15 min contact. The regenerability of N-halamine on PAM modified PET was studied by FTIR, titration and N analysis. After 30 regeneration cycles, the PAM-DVB network modified PET was still able to provide 100% reduction of HA-MRSA in 20 min contact.

The development of functionalized membranes with tunable pores and catalytic properties provides us an opportunity to manipulate the membrane pore structure, selectivity and reactivity. By introducing the functional groups into membrane pores, dissolved metal ions and reactive particles can be effectively immobilized within the polymer matrix for toxic chloro-organic and heavy metal remediation in water. A polyelectrolyte functionalized membrane platform with tunable pore size and ion exchange capacity has been developed for iron/iron oxide nano-catalyst synthesis and chlorinated organic compound (trichloroethylene, TCE and polychlorinated biphenyls, PCBs) degradation. Highly robust polyvinylidene fluoride (PVDF) microfiltration membranes are used as the support with cross-linked polyacrylic acid (PAA) filled in the pores. By varying the environmental pH, PAA hydrogels have either swelling or collapsing behavior, resulting in different effective membrane pore sizes for different separation purposes. Cation exchange groups (i.e. carboxyl groups) in PAA chains prevent the aggregation and leaching of nanoparticles (NPs) during in-situ synthesis and reaction. Depending on the catalyst loading and residence time, TCE and PCBs can be completely degraded by reduction of zero-valent iron and bimetallic iron/palladium NPs, or iron oxide catalyzed free radical oxidation at near-neutral pH. Biphenyl from PCB dechlorination can be further oxidized by hydroxyl radicals (OH•) generated from hydrogen peroxide (H2O2) decomposition. Hydroxybiphenyls and benzoic acid are identified as oxidation products. Line scan and elemental mapping in transmission electron microscopy (TEM) and X-ray photo electron spectroscopy (XPS) characterizations are conducted to understand the effect of iron surface transformation on NP reactivity, and to optimize the membrane functionalization. The same platform can also be used to remove toxic metal selenium in the scrubber water of coal-fired power plants. By reducing the salt concentration in water or increasing the residence time and temperature, the concentration of selenium oxyanions in functionalized membrane permeate can be reduced to less than 10 µg/L. Selenium is captured in membranes by both iron reduction to metallic selenium and iron oxide adsorption. The full-scale flat sheet functionalized membrane and spiral wound modules have also been developed. Iron NPs with alterable loadings are successfully synthesized inside the membrane module for real water applications.

Publics are facing a great challenge of infections from pathogens. Polyethylene terephthalate (PET) is widely used in health-care settings. It is vital to develop effective and regenerable antimicrobial PET. In this study, effective antibacterial modification of PET was achieved by immobilizing N-halamine biocide poly (N-chloroacrylamide) (PCA) onto PET through the formation of a surface interpenetrating network. The successful and uniform immobilization was confirmed by FTIR and XPS. The immobilization is durable to a 72 hours soxhlet extraction. Surface morphology of the fabrics did not significantly change after modification with IP less than 20%. The modified fabric can bring 100% reduction of 10e6 CFU/ml of several clinical important bacteria in 15 min contact. The regenerability of N-halamine on PAM modified PET was studied by FTIR, titration and N analysis. After 30 regeneration cycles, the PAM-DVB network modified PET was still able to provide 100% reduction of HA-MRSA in 20 min contact.

Pollution of water by herbicides and heavy metals has caused world wide concern because of the adverse effects of these pollutants on the environment, humans and wildlife. This has resulted in tighter legislation being imposed on the levels of these pollutants in drinking water. For example, the European Union (EU) has set the legislation in the drinking water Directive Admissible Concentration for a single herbicide to a maximum of 0.1 ppb. Despite the tight environmental pollution controls, isolated cases of pollutants exceeding their limits are still encountered. This would suggest that research towards the efficient and effective removal of these pollutants will be an on-going process. In this study, sorption of copper and some selected herbicides e.g. atrazine, benazolin and 2,4-dichlorophenoxyacetic acid (2,4-D) was undertaken on a conventional activated carbon and its modified series. A low level detection method was developed using High Performance Liquid Chromatography (HPLC) and this system was used to quantify the sorption capacity of the herbicides. In order to understand the sorption mechanism of the targeted pollutants, physical and chemical characterisation of the adsorbents was undertaken using a variety of techniques. These include, Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), Fourier Transform Infrared (FT-IR) method, pore size distribution and surface area measurements, elemental analysis, sodium capacity determination, zeta potential and pH titration. The sorption data were presented and analysed by conventional adsorption isotherms. Sorption of the herbicides was favoured on carbon samples with least oxygen content while the uptake of copper was strongest in oxidised carbons. Kinetic experimental data were analysed by a pseudo second order model and the Boyd kinetic model. Molecular structural configurations and the physico-chemical properties of the adsorbent played a crucial role in the sorption behaviour of the herbicides.

In the past decade there has been increasing interest in exploring the use of nanocellulose in medicine. However, the influence of the physicochemical properties of nanocellulose on the material´s biocompatibility has not been fully investigated.  In this thesis, thin films of nanocellulose from wood (NFC) and from Cladophora algae (CC) were modified by the addition of charged groups on their surfaces and the influence of these modifications on the material´s physicochemical properties and on cell responses in vitro was studied. The results indicate that the introduction of charged groups on the surface of NFC and CC results in films with decreased surface area, smaller average pore size and a more compact structure compared with the films of unmodified nanocelluloses. Furthermore, the fibres in the carboxyl-modified CC films were uniquely aggregated and aligned, a state which tended to become more prevalent with increased surface-group density. The biocompatibility studies showed that NFC films containing hydroxypropyltrime-thylammonium (HPTMA) groups presented a more cytocompatible surface than unmodified NFC and carboxymethylated NFC regarding human dermal fibroblasts. Carboxymethyl groups resulted in NFC films that promoted inflammation, while HPTMA groups had a passivating effect in terms of inflammatory response.  On the other hand, both modified CC films behaved as inert materials in terms of the inflammatory response of monocytes/macrophages and, under pro-inflammatory stimuli, they suppressed secretion of the pro-inflammatory cytokine TNF-α, with the effects of the carboxylated CC film more pronounced than those of the HPTMA CC material.  Carboxyl CC films showed good cytocompatibility with fibroblasts and osteoblastic cells. However, it was necessary to reach a threshold value in carboxyl-group density to obtain CC films with cytocompatibility comparable to that of commercial tissue culture material.  The studies presented here highlight the ability of the nanocellulose films to modulate cell behaviour and provide a foundation for the design of nanocellulose-based materials that trigger specific cell responses. The bioactivity of nanocellulose may be optimized by careful tuning of the surface properties. The outcomes of this thesis are foreseen to contribute to our fundamental understanding of the biointerface phenomena between cells and nanocellulose as well as to enable engineering of bioinert, bioactive, and bioadaptive materials.

The combined use of additive manufacturing (AM), biocompatible and biodegradable materials, cells and biomolecular signals is the most common biomanufacturing strategy applied in scaffold fabrication. AM processes offer a better control and the ability to actively design the porosity and interconnectivity of the scaffolds. When combined with clinical imaging data, these fabrication techniques can be used to produce constructs that are customised to the shape of the defect or injury. However, due to the hydrophobicity of the commonly used synthetic biopolymers, cell-seeding and proliferation efficiency are limited. Moreover, due to the tortuosity of the scaffolds, non-uniform cell distribution with rare cell adhesion in the core region also commonly exists. Additionally, the commercial available machines are not able to create multi-material and material gradient scaffolds that are required to mimic the nature of nature tissues. To overcome the above limitations, this thesis describes the development of a hybrid bio-additive manufacturing system, called plasma-assisted bioextruson system (PABS), to produce smart scaffold by combining multi-head polymer extrusion and the plasma surface modification layer by layer, in the same chamber. PABS allows not only multiple biomaterials printing with the multi-extrusion heads, but also enables in-process plasma surface modification for zonal plasma-treated scaffolds fabrication. The in-house user interface enables a high degree of scaffold design freedom as it allows users to create single or multi-material constructs with uniform pore size or pore size gradient by changing process parameters such as lay-down pattern, filament distance, feed rate and layer thickness. Water contact angle tests and in vitro biological tests confirm that the hydrophilicity of synthetic polymers is improved and cell attachment and proliferation are enhanced after the in-process plasma modification. The effect of plasma treatment is also investigated by using different plasma modification strategies and various plasma modification parameters, including the plasma deposition velocity and the distance between the plasma jet and the printed scaffolds. The biological results also show dependence between the surface modification strategies and cell proliferation. The mechanical compression results show that for a fixed plasma deposition velocity, the effect of changing the distance between the plasma head and the deposited material is not significant. However, for a fixed distance, the compressive modulus increases with the increase in the plasma deposition velocity.

Este trabalho foi desenvolvido em duas etapas: i) síntese, caracterização e aplicação de pontos quânticos de CdS, CdSe e CdTe em células solares. ii) modificação da superfície dos pontos quânticos de CdSe através de troca de ligante, seguida de caracterização e aplicação em células solares. Os pontos quânticos foram sintetizados utilizando acetatos de cádmio, selênio, telúrio e enxofre como precursores e ácido oleico como agente de estabilização. Na segunda etapa o ácido oleico foi substituído por ligantes com maior afinidade eletrônica pelos sítios de Cd2+: ácido 3-mercaptopropiônico, 4-ácido-mercaptobenzóico e ácido 11-mercaptoundecanóico. As amostras foram caracterizadas por UV-Vis, fluorescência, microscopia eletrônica de transmissão, difratometria de raios-X e voltametria cíclica. Adicionalmente, testes de solubilidade, análises de TGA e de RMN foram realizadas para confirmar a troca de ligante. Através dos resultados, verificou-se que todos os pontos quânticos sintetizados são adequados para sensibilização de TiO2 em dispositivos fotovoltaicos. No entanto, os pontos quânticos de CdSe e CdTe apresentaram fatores que evidenciam maior confinamento quântico, sendo que a maior estabilidade do éxciton foi obtida para o CdSe. Através das análises de RMN foi possível verificar que não existe apenas uma confirguração espacial preferencial para a adsorção do ligante sobre a superfície deste ponto quântico enquanto que curvas de corrente versus potencial e de eficiência de conversão de fóton incidente mostraram que a eficiência do dispositivo é fracamente dependente do ligante. Contudo, a troca de ligantes favorece a solubilidade em solventes com diferentes polaridades, inclusive água, o que amplia as possibilidades de aplicação dos pontos quânticos sintetizados neste trabalho. / This work was developed in two stages: i) synthesis, characterization and application of CdS, CdSe and CdTe quantum dots to assemble solar cells, ii) surface modification, characterization and application of CdSe quantum dots to assemble solar cells. The quantum dots were synthesized by using cadmium acetate, Se, S or Te as precursors and oleic acid as stabilizing agent. In the second stage the oleic acid capping layer was replaced by other ligands with higher electron affinity to Cd2+: 3-mercaptopropionic acid, 4-mercaptobenzoic acid and 11-mercaptoundecanoic acid. The samples were characterized by UV-Vis, fluorescence, transmission electron microscopy, x-ray diffractometry and cyclic voltammetry. Additionally, solubility tests, TGA analysis and NMR were performed to evaluate the CdSe surface modification. The results showed that all quantum dots synthesized are adequate to sensitize TiO2 in photovoltaic devices. However, CdSe and CdTe quantum dots presented better quantum confinement and the exciton generated in CdSe presented the higher stability. NMR analysis provided information about the non-preferential orientation for adsorption of the ligands on the CdSe surface, meanwhile measurements of current vs. potential and incident photon current efficiency showed a weak dependence of photovoltaic device efficiency with the nature of the ligand. On the other side, the surface modification favors the solubility in solvents with different polarizabilities, including water, widening the range for applications of the quantum dots synthesized in this work.

Neste trabalho exploramos o uso de diferentes técnicas de microestruturação de materiais poliméricos a laser, visando a obteção de superfícies que podem ser aplicadas tanto no desenvolvimento de dispositivos fotônicos quanto de materiais biomédicos. Primeiramente, estudamos a influência da energia de pulso e velocidade de translação sobre as microestruturas produzidas na superfície de filmes de poli(2-metóxi-5-(2-etil-hexiloxi)-1,4-fenileno vinileno) (MEH-PPV). Observamos que a rugosidade da superfície microestruturada aumentou significativamente com o aumento da energia de pulso e velocidade de translação. Além disso, determinamos o limiar de energia para remoção de material, distinguindo o intervalo de energia para a remoção do polímero daquele que causa somente alterações morfológicas. Uma vez que as condições de microestruturação com pulsos laser de femtossegundos foram determinadas, aplicamos tal abordagem para fabricar um dispositivo eletroluminescente microestruturado, sem danificar o polímero e a camada de óxido de índio-estanho, utilizada como contato. Em uma segunda vertente do trabalho, estudamos a influência da energia do pulso ultracurto sobre as propriedades físico-químicas de filmes de quitosana. Neste caso, determinamos o limiar de energia para que ocorra mudança estrutural e remoção de material polimérico. Com isso, produzimos microestruturas com características mais hidrofílicas, além de superfícies com diferentes estruturações superficiais, que foram utilizadas para investigar seu potencial no estudo da formação de biofilme de Staphylococcus aureus. Neste caso, produzimos microestruturas com dimensões de 500 &#956;m2 e diferentes periodicidades (variando de 4 a 12 &#956;m) na superfície de filmes de quitosana e polimetilmetacrilato (PMMA). Com essas microestruturas, observamos distintos comportamentos para a formação de biofilme; no caso do PMMA, não houve distinção de desenvolvimento; quanto às amostras de quitosana, observamos uma preferência das bactérias por superfícies mais rugosas e regiões de bordas das microestruturas. Por fim, em uma terceira vertente do trabalho, utilizamos o método de estruturação direta por interferência para fabricar microestruturas periódicas em membranas de poliuretano, usando pulsos de nanossegundos. Com esse método, produzimos microestruturas de alta qualidade na superfície de membranas de poliuretano, com diferentes periodicidades (variando de 500 nm até 5 &#956;m). Essa microestruturação permitiu a obtenção de amostras com comportamento de molhamento anisotrópico. De maneira geral, os resultados aqui apresentados, além de demonstrar a potencialidade das técnicas de microfabricação a laser, fornecem importantes informações sobre os parâmetros ótimos para microfabricação em filmes poliméricos, visando aplicações tanto em dispositivos fotônicos e optoeletrônicos quanto em biomateriais. / In this work we explored the use of laser micromachining methods to structure polymeric materials, aiming to obtain surfaces that can be applied in the development of photonic devices as well as biomedical materials. Firstly, we investigated the influence of pulse energy and translation speed on microstructures fabricated on the surface of poly[2-methoxy-5- (2\'-ethylhexyloxy)-p-phenylenevinylene] (MEH-PPV) films. We observed that the roughness of the microstructured surface significantly increased with the pulse energy and translation speed. Besides, we determined the energy threshold for material removal, distinguishing the energy range for polymer removal from that causing only structural changes. Once the proper laser micromachining conditions were determined, we were able to apply such approach to fabricate a functional microstructured electroluminescent device, without disrupting the indium tin oxide layer used as the contact for the devices. In the second part of the work, we studied the influence of femtosecond pulses on the structuring process of chitosan films. In this case, we determined the threshold energy that leads to structural change and material removal. We have been able to produced microstructures with hydrophilic characteristics, in addition to surfaces with different structuring that were used to study the formation of Staphylococcus aureus biofilm. For such purpose we produced microstructured areas of 500 &#956;m2 and different periods (ranging from 4 to 12 &#956;m) on the surface of chitosan and poly(methyl methacrylate)(PMMA) films. With these microstructures we observed different behaviors in the biofilm formation; in the case of PMMA, there was not distinction of development; concerning the chitosan samples we observed preferential bacterial growth on the rougher regions of the microstructures. Lastly, in a third part of the study, we used the method of direct laser interference patterning to fabricate periodic microstructures on polyurethane membranes, using nanosecond pulses. With this method, we produced high quality microstructures on the surface of polyurethane with different periodicity (from 500 nm to 5.0 &#956;m). This approach allowed obtaining samples with anisotropic wetting behavior. In general, the results presented here, in addition to demonstrating the potential of the laser micromachining methods to structure polymeric samples, provides important information about the optimal parameters to micromachining of polymer films, aiming at applications in photonic devices, optoelectronics and biomaterials.