The commodity plastics industry is dominated by semicrystalline polymers, which generally display high toughness relative to amorphous polymers but typically suffer from low strength and modulus. Researchers have shown that the addition of nanoparticles (NPs) to these semicrystalline matrices can result in materials with enhanced properties relative to the neat systems. The arrangement of these NPs into anisotropic sheet-like structures appears to endow these processed polymer nanocomposites (PNCs) with further improved mechanical properties relative to PNCs where the NP morphology remains well-dispersed. However, there is currently no appropriate methodology in the literature with which to quantitatively correlate the extent of NP organization to the enhancement in mechanical properties. Additionally, isothermal crystallization (the current processing technique of choice for this class of PNCs) results in numerous grain boundaries. While entanglements across grains can limit issues associated with failure, grain boundaries can also be undesirable for the modulus of the material. In this dissertation, we methodically investigate several key topics related to the above. We first present our modifications to the correlation function approach of Strobl and Schneider, which was originally developed to characterize the structural parameters of neat semicrystalline polymers and their blends, that allow us to apply it to isothermally crystallized poly(ethylene oxide) (PEO) PNCs. We select PEO due to the relative ease with which mobile silica NPs can be dispersed within the matrix. Next, we characterize these materials using the generally used large beam size typical of laboratory-scale and synchrotron X-ray scattering instruments. In this study, we show that our adaptations to the correlation function approach allow for the quantitative evaluation of the NP ordering process as a function of isothermal crystallization temperature. The same systems are then characterized with a microfocus synchrotron X-ray scattering beam guided by an autonomous experimentation protocol, which allows for a detailed, granular mapping of the structural parameters of these materials. The much smaller beam reveals spatial morphological heterogeneity in both the neat and PNC systems due to the grain size being on the order of the dimensions of the microbeam as opposed to those of the larger beam. Hence, the combination of the large and microfocus beam provides a comprehensive view of these systems, with varying degrees of granularity. We also find quantitative evidence that demonstrates that NPs organize parallel to the direction of polymer crystal growth, a phenomenon which has previously only been shown in the literature in a qualitative fashion. Having established the physics of the NP ordering process in isothermally crystallized PNC systems, we turn to the zone annealing (ZA) technique as inspiration to approach more uniform, unidirectionally oriented NP morphologies. ZA, which has found extensive use in the production of ultra-pure semiconductors for electronics applications, proceeds by translating a sample at a constant velocity over a well-defined temperature gradient. This directional processing technique has been shown to result in the reduction of grain boundaries when applied to semicrystalline polymers. Since the PNC is a more complicated system than the neat matrix, we first perform studies of zone annealed neat PEO. Our experimental, analytical, and numerical investigations validate a crucial directional crystallization theory proposed by Lovinger and Gryte, who were among the first to apply ZA to semicrystalline polymers; our experimental evidence confirms the existence of a critical ZA velocity (v_crit) below which directional crystallization occurs and above which the process is closer in spirit to isothermal crystallization. Having determined the mechanism driving the ZA of neat PEO, we then turn to the ZA of PEO-based PNCs. Through our studies, we find that it is imperative to minimize or eliminate sample flow during the procedure, as otherwise the NPs order in disparate directions. Our subsequent redesign of the sample preparation protocol, such that the material is pressed between two glass coverslips separated by Teflon spacers, leads to extensive unidirectional organization of NPs that persists throughout the film at slow enough ZA velocities, as evidenced from X-ray scattering experiments. Hence, this dissertation systematically examines questions relevant to understanding how to obtain uniform, unidirectional NP organization in semicrystalline PNCs, with relevance to applications requiring enhanced properties.

A non-invasive method to quantify the stress distribution in polymer-based materials is presented through the piezospectroscopic calibration of alumina-epoxy nanocomposites. Three different alumina volume fraction nanocomposites were created and loaded under uniaxial compression in order to determine the relationship between applied stress and the frequency shift of the R-lines produced by alumina under excitation. Quantitative values for six piezospectroscopic coefficients were obtained which represent the stress-sensing property of the nanocomposites. The results were applied to an alumina-filled adhesive in a single lap shear configuration demonstrating the capability of the technique to monitor R-line peak positions with high spatial resolution and assess the stress distribution within the material prior to failure. Additionally, particle dispersion and volume fraction were confirmed with spectral intensities, introducing a novel experimental method for the assessment of quality in manufacturing of such nanocomposites. Results were further used to initiate studies in determining the load transfer to the nanoparticles and assessing the fundamental driving mechanisms.

In this work, we studied the electronic behavior of polymer-derived ceramics (PDCs) and applied them for the synthesis of carbon nanotube reinforced ceramic nanocomposites and ceramic MEMS (Micro-Electro-Mechanical Systems) structures. Polymer-derived SiCN ceramics were synthesized by pyrolysis of a liquid polyureasilazane with dicumyl peroxide as thermal initiator. The structural evolution during pyrolysis and post-annealing was studied using FTIR, solid state NMR and Raman. The results revealed that the resultant ceramics consisted of SiCxNx-4 as major building units. These units were connected with each other through C-C/C=C bonds or by shearing N/C. The amount of sp2 free carbon strongly depends on composition and processing condition. Electron paramagnetic resonance (EPR) was used to investigate electronic structure of PDCs; the results revealed that the materials contain unpaired electron centers associated with carbons. Electronic behavior of the SiCN ceramics was studied by measuring their I-V curves, temperature dependence of d.c.-conductivities and impendence. The results revealed that the SiCN ceramics exhibited typical amorphous semiconductor behavior, and their conductivity varied in a large range. The results also revealed that the materials contain more than one phase, which have the different electronic behavior. We explored possibility of using polymer-derived ceramics to make ceramic MEMS for harsh environmental applications with a lithography technique. The cure depth of the polymer precursor was measured as a function of UV intensity and exposure time. The experimental data was compared with the available theoretical model. A few typical SiCN parts were fabricated by lithography technique. We also prepared carbon nanotube reinforced ceramic nanocomposites by using PDC processing. The microstructures of the composites were characterized using SEM and TEM; the mechanical properties were studied characterized using nanoindentation. The significant improvement in mechanical properties was observed for the nanocomposites.

Carbon nanofibers (CNFs) used as nano-scale reinforcement have been extensively studied since they are capable of improving the physical and mechanical properties of conventional fiber reinforced polymer composites. However, the properties of CNFs are far away from being fully utilized in the composites due to processing challenges including the dispersion of CNFs and the viscosity increase of polymer matrix. To overcome these issues, a unique approach was developed by making carbon nanopaper sheet through the filtration of well-dispersed carbon nanofibers under controlled processing conditions, and integrating carbon nanopaper sheets into composite laminates using autoclave process and resin transfer molding (RTM). This research aims to fundamentally study the processing-structure-property-performance relationship of carbon nanopaper-based nanocomposites multifunctional applications: a) Vibrational damping. Carbon nanofibers with extremely high aspect ratios and low density present an ideal candidate as vibrational damping material; specifically, the large specific area and aspect ratio of carbon nanofibers promote significant interfacial friction between carbon nanofiber and polymer matrix, causing higher energy dissipation in the matrix. Polymer composites with the reinforcement of carbon nanofibers in the form of a paper sheet have shown significant vibration damping improvement with a damping ratio increase of 300% in the nanocomposites. b) Wear resistance. In response to the iv observed increase in toughness of the nanocomposites, tribological properties of the nanocomposite coated with carbon nanofiber/ceramic particles hybrid paper have been studied. Due to high strength and toughness, carbon nanofibers can act as microcrack reducer; additionally, the composites coated with such hybrid nanopaper of carbon nanofiber and ceramic particles shown an improvement of reducing coefficient of friction (COF) and wear rate. c) High electrical conductivity. A highly conductive coating material was developed and applied on the surface of the composites for the electromagnetic interference shielding and lightning strike protection. To increase the conductivity of the carbon nanofiber paper, carbon nanofibers were modified with nickel nanostrands. d) Electrical actuation of SMP composites. Compared with other methods of SMP actuation, the use of electricity to induce the shape-memory effect of SMP is desirable due to the controllability and effectiveness. The electrical conductivity of carbon fiber reinforced SMP composites can be significantly improved by incorporating CNFs and CNF paper into them. A vision-based system was designed to control the deflection angle of SMP composites to desired values. The funding support from National Science Foundation and FAA Center of Excellence for Commercial Space Transportation (FAA COE CST) is acknowledged.

The first part of the study deals with the preparation of carbon nanotube/polymer nanocomposite materials. The dispersion of multi-walled carbon nanotubes (MWNTs) using trifluoroacetic acid (TFA) as a co-solvent and its subsequent use in polymer nanocomposite fabrication is reported. The use of carbon nanotube/ polymer nanocomposite system for the fabrication of organic solar cells is also studied. TFA is a strong but volatile acid which is miscible with many commonly used organic solvents. Our study demonstrates that MWNTs can be effectively purified and readily dispersed in a range of organic solvents including dimethyl formamide (DMF), tetrahydrofuran (THF), and dichloromethane when mixed with 10 vol% trifluoroacetic acid (TFA). X-ray photoelectron spectroscopic analysis revealed that the chemical structure of the TFA-treated MWNTs remained intact without oxidation. The dispersed carbon nanotubes in TFA/THF solution were mixed with poly(methyl methacrylate) (PMMA) to fabricate polymer nanocomposites. A good dispersion of nanotubes in solution and in polymer matrices was observed and confirmed by SEM and optical microscopy study. Low percolation thresholds of electrical conductivity were observed from the fabricated MWNT/PMMA composite films. A carbon nanotube/ polymer nanocomposites system was also used for the fabrication of organic solar cells. A blend of single-wall carbon nanotubes (SWNTs) and poly3-hexylthiophene (P3HT) was used as the active layer in the device. The device characteristics showed that the fabrication of the solar cells was successful without any shorts in the circuit. The second part of the study deals with the preparation and characterization of electrode and electrolyte materials for lithium ion batteries. A system of lithium trifluoroacetate/ PMMA was used for its study as the electrolyte in lithium battery. A variety of different processing conditions were used to prepare the polymer electrolyte system. The conductivity of the electrolyte plays a critical role in the high power output of a battery. A high power output requires fast transport of lithium ions for which the conductivity of the electrolyte must be at least 3 x 10^-4 S/cm. Electrochemical Impedance Spectroscopy (EIS) was used to determine the conductivity of the polymer electrolyte films. Among the different processing conditions used to prepare the polymer electrolyte material, wet films of PMMA/salt system prepared by using 10vol% of TFA in THF showed the best results. At about 70wt% loading of the salt in the polymer, the conductivity obtained was about 1.1 x 10^-2 S/cm. Recently, the use of vanadium oxide material as intercalation host for lithium has gained widespread attention. Sol-gel derived vanadium oxide films were prepared and its use as a cathode material for lithium ion battery was studied. The application of carbon nanotubes in lithium ion battery was explored. A carbon nanotube /block copolymer (P3HT-b-PS) composite was prepared and its potential as an anode material was evaluated.

Plasma spray processing is a technique that is used extensively in thermal barrier coatings on gas and steam turbine components, biomedical implants and automotive components. Many processing parameters are involved to achieve a coating with certain functionality. The coating could be required to function as thermal barrier, wear resistant, corrosion resistant or a high temperature oxidation resistant coating. Various parameters, such as, nozzle and electrode design, powder feeding system, spray distances, substrate temperature and roughness, plasma gas flow rates and others can greatly alter the coating quality and resulting performance. Feedstock (powder or solution precursor) composition and morphology are some of the important variables, which can affect the high end coating applications. The amount of heat a plasma plume has to offer to the particles being processed as a coating depends primarily on the dissociation of the atoms of gaseous mixtures being used to create the plasma and the residence time required for the particle to stay in the flame. The parameters that are conducive for nanostructured retention could be found out if the residence time of the particles in the flame and the available heat in the plume for various gas combinations could be predicted. If the feedstock is a liquid precursor instead of a powder feedstock, the heat that has to be offered by the plasma could be increased by suitable gas combination to achieve a good quality coating. Very little information is available with regard to the selection of process parameters and processing of nano materials feedstock to develop nanostructured coatings using plasma spray. In this study, it has been demonstrated that nano ceramics or ceramic composites either in the form of coatings or bulk free form near net components could be processed using DC plasma spray. For powder feedstock, analytical heat transfer calculations could predict the particle states for a given set of parameters by way of heat input from the plasma to the particles. The parameter selection is rendered easier by means of such calculations. Alumina nano ceramic particles are processed as a coating. During Spray drying, a process of consolidation of nano alumina particles to spherical agglomerates, parameter optimization for complete removal of moisture has been achieved. The parameters are tested for alumina nanoparticles with a plasma torch for the veracity of calculations. The amount of heat transfer from the surface of the agglomerates to the core has been quantified as a function of velocity of particles. Since preparation of nanostructured feedstock for plasma spray is expensive and cumbersome, alternative solution precursor route for direct pyrolysis of precursor to coating has been studied in case of nanocrystalline rare earth oxides. Thus, it has also been shown by this research that nanostructured coatings could be either from a powder feedstock or a solution precursor feedstock. MoSi2-Si3N4, Ni-Al2O3, W-HfC nano ceramic composite systems have been processed as a bulk free form nanocomposite with 60-70% retained nanostructures. The importance of selection of substrates, roughness and the substrate temperature for development of free form bulk components has been highlighted. The improvement in mechanical and high temperature properties associated with having such nanostructured coatings or bulk nanocomposites are revealed. These nanostructured coatings are known for their low thermal conductivity, high wear resistance and can be potentially used as steam and gas turbines coatings for improved thermal efficiency. In summary, bulk nanocomposite through plasma spray processing is a viable alternative to conventional processes such as sintering, HIP for high fracture toughness and hardness applications.

Nanotechnology is the manipulation of matter and devices on the nanometer scale. Below the critical dimension length of 100nm, materials begin to display vastly different properties than their macro- or micro- scale counterparts. The exotic properties of nanomaterials may trigger the start of a new technological revolution, similar to the electronics revolution of the late 20th century. Current applications of nanotechnology primarily make use of nanoparticles in bulk, often being made into composites or mixtures. While these materials have fantastic properties, organization of nano and microstructures of nanoparticles may allow the development of novel devices with many unique properties. By analogy, bulk copper may be used to form the alloys brass or bronze, which are useful materials, and have been used for thousands of years. Yet, organized arrays of copper allowed the development of printed circuit boards, a technology far more advanced than the mere use of copper as a bulk material. In the same way, organized assemblies of nanoparticles may offer technological possibilities far beyond our current understanding. In the first project, 1D assemblies of nanoparticles were explored. 1D anisotropic assemblies of nanoparticles are the simplest organized nanostructures which may be fabricated. One of the greatest difficulties in developing commercial products is in the transfer of a process from the laboratory to manufacturing scale. While many techniques may be used to develop 1D assemblies in lab, simple techniques are needed to allow the fabrication of these assemblies on a large, cost effective scale. Use of shear, shown previously to induce colloidal ordering in solutions, is a technique that may be readily adapted from the coatings industry as a process for forming 1D assemblies, if the optimal conditions can be found. Atomic force microscopy was used to study the role of shearing forces produced by drawdown and spraying application in the formation of 1D assemblies of nanoparticles. Formation of 1D strings was observed to increase with greater application of simple shear, but greater spraying forces were found to decrease formation of strings. This is explained in terms of greater simple shear providing a greater driving force for string formation, while greater spraying shear acted to irreversibly disperse the particles. The second project focused on the development of a learning module for education of students at various academic levels on the significance of the surface area of nanomaterials. This project was commissioned by the Global Waste Research Institute, a multidisciplinary organization based at Cal Poly, concerned with performing research and education in areas related to waste management, particularly of emerging waste streams. As nanotechnology and nanoparticles become more prevalent in consumer products and industrial processes, the volume of nanowaste is increasing rapidly. To address challenges associated with processing this unique form of waste, understanding of the fundamental processes controlling the unique properties of nanoparticles is necessary. A learning module was developed using a laboratory demonstration and video presentation to illustrate concepts related to differences in the properties between microparticles and nanoparticles. The laboratory demonstration was designed to be simple to understand, and quick, simple, and inexpensive to perform. The video presentation was designed to be a 15 minute presentation relating the concepts of nanotechnology, nanoparticles, surface area, and fundamental differences as compared to conventional materials. Dispersions of particles within aqueous media were used as a framework for the discussion, in a manner comprehensible by students ranging from 12th grade high school students to graduate students in relevant programs. The third and final project focused on self-assembly of particles in nematic liquid crystalline colloids. Dispersions of colloidal particles in liquid crystals (LCs) are a relatively new set of composite materials, host to a variety of interactions not seen in colloids in isotropic media. Presence of colloidal particles disrupts the local nematic director, resulting in a loss of long-range elastic energy. Interactions between particles and LC molecules results in dipolar or quadrupolar defects, depending on the nature of the interactions between particle and LC. The loss of long-range elastic energy can be minimized through aggregation of particles. The defects formed by interactions between particles and LC stabilize these aggregations as linear chains, either along the nematic director in the case of dipolar defects, or at an offset angle in the case of quadrupolar defects. Dispersions of silica microspheres in the nematic phase of a thermotropic liquid crystal were studied using polarizing light microscopy. Strong homeotropic anchoring was observed, indicated by the abundant formation of hedgehog defects. These defects were found to play a role in self-assembly of particles along the nematic director, resulting aggregates containing up to a dozen aligned particles. In addition, particles were observed to aggregate in chains along grain boundaries in the liquid crystal, acting to stabilize the high energy interface between different grain directions, an effect not previously reported in the scientific literature for nematic colloids.

As a preliminary starting point for the present study, physical and mechanical properties of polypropylene nanocomposites (PPNCs) for samples received from Queen's University Belfast have been evaluated. Subsequently, polymer/clay nanocomposite material has been produced at Bradford. Mixing and processing routes have been explored, and mechanical properties for the different compounded samples have been studied. Clay intercalation structure has received particular attention to support the ultimate objective of optimising tensile and fracture behaviour of isotropic and die-drawn PPNCs. Solid-state molecular orientation has been introduced to PPNCs by the die-drawing process. Tensile stress-strain measurements with video-extensometry and tensile fracture of double edge-notched tensile specimens have been used to evaluate the Young¿s modulus at three different strain rates and the total work of fracture toughness at three different notch lengths. The polymer composite was analyzed by differential scanning calorimetry, thermogravimetric analysis, polarizing optical microscopy, wide angle x-ray diffraction, and transmission electron microscopy. 3% and 5% clay systems at various compatibilizer (PPMA) loadings were prepared by three different mixing routes for the isotropic sheets, produced by compression moulding, and tensile bars, produced by injection moulding process. Die-drawn oriented tensile bars were drawn to draw ratio of 2, 3 and 4. The results from the Queen's University Belfast samples showed a decrement in tensile strength at yield. This might be explained by poor bonding, which refers to poor dispersion. Voids that can be supported by intercalated PP/clay phases might be responsible for improvement of elongation at break. The use of PPMA and an intensive mixing regime with a two-step master batch process overcame the compatibility issue and achieved around 40% and 50% increase in modulus for 3% and 5% clay systems respectively. This improvement of the two systems was reduced after drawing to around 15% and 25% compared with drawn PP. The work of fracture is increased either by adding nanoclay or by drawing to low draw ratio, or both. At moderate and high draw ratios, PPNCs may undergo either an increase in the size of microvoids at low clay loading or coalescence of microvoids at high clay loading, eventually leading to an earlier failure than with neat PP. The adoption of PPMA loading using an appropriate mixing route and clay loading can create a balance between the PPMA stiffness effect and the degree of bonding between clay particles and isotropic or oriented polymer molecules. Spherulites size, d-spacing of silicate layers, and nanoparticles distribution of intercalated microtactoids with possible semi-exfoliated particles have been suggested to optimize the final PPNCs property. / SABIC

Les infections associées au milieu hospitalier demeurent une cause majeure de mortalité et de morbidité dans le monde, malgré plusieurs décennies dédiées à promouvoir une meilleure surveillance et des méthodes de désinfection plus complètes. La capacité des bactéries pathogènes à survivre sur des substrats solides a été identifiée comme un facteur clé de la pathogenèse de ces infections, en multipliant les sources de transmission et de contamination. Au niveau de la recherche, cette situation s’est récemment traduite par un intérêt marqué pour le développement de revêtements antibactériens novateurs pouvant constituer une ligne de défense complémentaire contre la colonisation bactérienne de surfaces, pourvu qu’ils puissent résister à l’environnement rigoureux des établissements de santé. Dans cette thèse, nous avons émis l'hypothèse qu'un revêtement antibactérien avec une stabilité supérieure pouvait être déposé en utilisant un procédé plasma modulable, de sorte que les propriétés du revêtement résultant pourraient être adaptées aux exigences de différentes situations ou applications. Par conséquent, des revêtements nanocomposites de carbone amorphe adamantin contenant de l'argent (Ag-DLC) ont été développés et étudiés comme plate-forme polyvalente pour des surfaces antibactériennes. L’intérêt de ce matériau réside dans la combinaison des excellentes propriétés mécaniques, de la résistance à l'usure et de l'inertie chimique du carbone amorphe adamantin avec les propriétés antibactériennes à large spectre des nanomatériaux d'argent au sein d’un même revêtement déposé par plasma. Ce travail a d'abord identifié les défis de conception spécifiquement associés au développement de revêtements antibactériens pour le milieu hospitalier. Des analyses approfondies des revêtements Ag-DLC ont ensuite démontré une bonne efficacité antibactérienne in vitro ainsi qu’une stabilité des propriétés, de la structure et de l’état chimique des revêtements dans le temps. L'étendue de la polyvalence des revêtements Ag-DLC a été évaluée au travers de l’identification des mécanismes de croissance principaux, permettant d’obtenir des informations essentielles sur la façon dont les propriétés des films, telles que la dureté, la teneur et la distribution d’argent, pouvaient être contrôlées en ajustant des paramètres spécifiques du dépôt plasma. De plus, un traitement de surface in situ a été développé pour surmonter les problèmes de délamination et a montré la capacité de favoriser l'adhérence de revêtements DLC sur des substrats métalliques. Dans l'ensemble, cette étude a mis en évidence l'importance de la stabilité dans l'application des revêtements antibactériens et a démontré le vaste potentiel des procédés plasma pour le dépôt de revêtements antibactériens stables avec des propriétés adaptables. / Healthcare-associated infections remain a major cause of mortality and morbidity worldwide, with a substantial financial burden on society, despite decades of monitoring and disinfection efforts. The ability of pathogenic bacteria to survive on solid substrates has emerged as a key contributing factor in the pathogenesis of these infections by multiplying the sources of transmission and contamination. This has prompted investigations into the development of innovative antibacterial coatings, which could provide a complementary barrier against bacterial colonization of surfaces provided that they can withstand the harsh operating environment of healthcare facilities. In this thesis, we hypothesized that an antibacterial coating with superior stability could be deposited using a tailorable plasma process, so that the resulting coatings’ properties could be adapted to match the requirements of different situations or applications. Therefore, silver-containing diamond-like carbon (Ag-DLC) nanocomposite coatings were developed and investigated as a versatile platform material for antibacterial surfaces. The interest of this material lies in the combination of the excellent mechanical properties, wear-resistance and chemical inertness of diamond-like carbon with the broad-spectrum antibacterial properties of silver nanomaterials in a single, plasma-deposited coating. This work first identified the specific design challenges associated with the development of antibacterial coatings for healthcare environments. Thorough investigations of Ag-DLC coatings then revealed good antibacterial efficacy in vitro as well as stability of the coatings’ properties, structure, and chemistry over time. The extent of the tailorability of Ag-DLC coatings was also assessed through the identification of the main growth mechanisms, providing insights on how the film’s properties, such as the hardness, silver content, and silver distribution, could be controlled by adjusting specific plasma deposition parameters. Furthermore, an in situ interface plasma treatment was developed to overcome delamination issues and showed the ability to promote the adhesion of high stress DLC coatings on metallic substrates. Overall, this study highlighted the importance of stability in the application of antibacterial coatings and demonstrated the vast potential of plasma processes for the deposition of stable antibacterial coatings with tunable properties.

Ce travail de recherche comprenait deux volets. Le premier volet avait comme objectif général d’améliorer les propriétés barrières et mécaniques de la couche de surface devant constituer le revêtement multicouche (MC) pour le bois. L’objectif général du second volet visait quant à lui à augmenter l’adhérence du système [MC/surface du bois]. Dans le premier volet, des revêtements polymérisés sous ultraviolets (UV) pour la couche de surface ont été préparés en utilisant trois grades de nanoargile commerciale dispersés (1 et 3 % en masse totale dans la formulation) dans un oligomère commercial du type époxy acrylate. La morphologie des revêtements nanocomposites a été étudiée par diffraction des rayons X et par microscopie électronique à transmission (MET). La propriété barrière, la clarté optique ainsi que les propriétés mécaniques de ces revêtements ont également été évalués. Dans le deuxième volet, les surfaces de bois du bouleau jaune (Betula alleghaniensis Britton) ont été protégées avec six types de MC. Les formulations polymérisables sous UV pour la couche d’imprégnation et la couche de surface contenaient respectivement la nanosilice (NS : 0 et 0,5 %) et la nanoargile (NA : 0, 1 et 3 %). La morphologie de la section transversale du système [MC/surface du bois] a été étudiée par microscopie électronique à balayage (MEB) et par MET. Enfin, l’adhérence du système [MC/surface du bois] a été investiguée en fonction de l’humidité relative (HR). Les images de MET révèlent que la C30B a été moins bien dispersée que la C10A et la C15A, lesquelles ont donné lieu à l’obtention des revêtements nanocomposites dont la morphologie serait du type intercalée. Les nanoargiles ont un effet autant sur la propriété barrière que sur la clarté optique. Parmi les trois grades de nanoargiles, la C10A serait idéale pour une application pratique (salles de bains) et a été utilisée comme agent de renfort pour la couche de surface des MC. La contrainte d’adhérence du système [MC/surface du bois] a été plus élevée pour les échantillons conditionnés à 80% d’HR que pour ceux conditionnés à 40% d’HR. Le revêtement multicouche 5 (0,5% NS – 1% NA) serait idéal comme système de protection. / This research consists in two sections. The main objective of the first section was to improve barrier and mechanical properties of topcoats for wood furniture; while for the second section, the main objective was to increase the adhesion of multilayer coatings on wood surfaces. In the first section, free standing UV-cured coatings were prepared by using three different types of commercial organoclays. These nanoparticles were dispersed (1 and 3 wt % into the formulation) into a commercial epoxy acrylate oligomer. The morphology of these nanocomposites was studied by X-ray diffraction and by transmission electron microscopy (TEM). The barrier property (WVTR: water vapor transmission rate), optical clarity and mechanical tests of these nanocomposites were also assessed. In the second section, surfaces of yellow birch wood (Betula alleghaniensis Britton) were protected with six different types of multilayer coatings (MCs). Prepared primer and topcoat UV-curable formulations constituting these MCs contained, respectively nanosilica (NS: 0 and 0.5 wt %) and nanoclay (NC: 0, 1 and 3 wt %). The morphology of the cross-section of coated wood samples was studied by means of both scanning and transmission electron microscopy (SEM and TEM analysis respectively). The adhesion strength of these MCs on wood surfaces was assessed as a function of relative humidity (RH). TEM images reveal that C30B was not found to be dispersible into the acrylate matrix; while both UV-cured nanocomposites containing C10A and C15A respectively seemed to have an intercalated morphology. All the organoclays used in this study have had an effect on both WVTR and optical clarity. Among the three different types of organoclays, C10A appears to be the ideal reinforcing agent for practical application (bathrooms) and was used for topcoat constituting MCs on wood surfaces. The adhesion strength of coated wood samples conditioned at 80% RH was higher than that obtained on those conditioned at 40% RH. Multilayer coating 5 (0.5% NS–1% NC) appears to be the ideal protection system.