Thesis (MSc)--Stellenbosch University, 2002. / ENGLISH ABSTRACT: Aqueous polyurethane (PU) dispersions were synthesized for the use in paper coatings. These PUs contained a polyester polyol soft segment (content of 60-70%) and a urethane hard segment (content of 30-40%). This was followed by grafting using four different grafting agents. Triethylamine (TEA) was used as the neutralizing agent. The polyester polyol segment consisted of neopentyl glycol (NPG), adipic acid, 1,4-cyclohexane dicarboxylic acid (1,4-CHOCA) and 2-phosphonobutane-1 ,2,4- tricarboxylic acid (PSTCA), while the urethane hard segment consisted of hydrogenated 4,4-diphenylmethane diisocyanate, dimethylolproponic acid (OMPA), 3-hydroxypivalic acid (HPA) and hydroxyethylene methacrylate (HEMA). The grafting agents used were lauryl methacrylate (LMA), n-butyl methacrylate (n-SMA), methyl methacrylate (MMA) and styrene. Two different polyester polyols were synthesized, one containing 10% phosphate and the other none. The polyols were characterized in terms of their acid value, hydroxyl value and molecular mass. The PUs synthesized from the polyol containing 0% phosphate were grafted with LMA, while the phosphate-containing PUs were grafted with each of the all four grafting agents. The resulting dispersions were applied to paperboard, and then dried at a maximum temperature of 100°C. The PU-coated paperboard was characterized using the moisture vapour transmission rate (MVTR), and scanning electron microscopy (SEM) techniques. PU films (not supported by paper, stand alone) were prepared by heating the PU dispersion in Teflon holders up to 130°C for 6 hours. The dried films were then characterized by thermogravimatric analysis (TGA), differential scanning calorimetry (OSC), dynamic mechanical analysis (OMA) and Fourier transform infrared spectroscopy (FTIR). MVTR-analysis showed that the phosphated PU coatings had a minimum MVTR-value at 0% grafting, and that its overall MVTR-values were much lower than that of the non-phosphated PU coatings. SEM-analysis showed that the phosphated PU coatings had no pinholes at a maximum of 8% grafting, while the non-phosphated PU coatings showed pinholes at all levels of grafting. OMA-analysis showed that the phosphated PU samples had higher Tg's (Tg onset between O-S°C)than that of the non-phosphated PU samples (Tgonset below -SO°C). / AFRIKAANSE OPSOMMING: POLI-URETAAN DISPERSIES VIR PAPIER BEDEKKINGS Waterige poli-uretaan (PU) dispersies is gesintetiseer vir gebruik as papierbedekkings. Hierdie poli-uretane het 'n poliester poli-ol sagte segment (60-70% inhoud) en 'n uretaan harde segment (30-40% inhoud) bevat. Die poli-uretane is met vier verskillende ent-middels geêent. Trietielamien (TEA) is as neutraliseermiddel gebruik. Die poli-ester poli-ot segment het bestaan uit: neopentielglikol (NPG), adipiensuur, 1,4-sikloheksaandikarboksielssuur (1,4- SHDKS) en 2-fosfonobutaan-1 ,2,4-trikarboksielssuur (FSTKS). Die uretaan harde segment het bestaan uit: hidrogeneerde 4,4-difenielmetaandiisosianaat, dimetielpropioonsuur (DMPS), 3-hidroksipivaalsuur (HPS) en hidroksietileenmetakrilaat (HEMA). Laurielmetakrilaat (LMA), n-butielmetakrilaat (n-SMA), metielmetakrilaat (MMA) en stireen is as entmiddels gebruik. Twee verskillende poli-ester polihidroksie verbindings is gesintetiseer: een met 10% fosfaat en een met geen fosfaat, en gekarakteriseer in terme van hulle suurwaardes, hidroksiwaardes en molekulêre massas. Die PUs wat vanaf die fosfaat-bevattende poli-ol gesintetiseer is, is met LMA geêent, terwyl die fosfaat-bevattende PUs met al vier entmiddels geêent is. Papier (Eng. paperboard) is met hierdie dispersies bedek en by 100°C gedroog. Die PU-bedekte papier is gekarakteriseer in terme van vogdeurlaatbaarheidstransmissie (Eng: MVTR - the moisture vapour transmission rate), en skandeerelektonmikroskopie (SEM). PU-films wat nie deur papier gestut is nie is ook voorberei deur die verhitting van die PU dispersies in Teflon houers (130°C, 6 ure). Die droë films is daarna gekarakteriseer deur middel van termogravimetriese analise (TGA), differensiêle skandeerkalorimetrie (DSC), dinamiese meganiese analise (OMA) en Fourier-transformasie infrarooispektroskopie (FTIR). Resultate van MVTR analises het getoon dat die fosfaat-bevattende PU bedekkings 'n mimimum MVTR-waarde by 0% enting gehad het, en dat die totale MVTR waardes baie laer was as die van die nie-fosfaatbevattende bedekkings. SEM het gewys dat die fosfaat-PU bedekkings by 8% enting geen mikrogaatjies (Eng. pinholes) gehad net nie, terwyl die PU bedekings met geen fosfaat mikrogaatjies (Eng. pinholes) by alle vlakke van enting gehad het. OMA analises het getoon dat die monsters van die fosfaatbevattende PU hoër Tg waardes gehad het (Tg begin tussen 0 en 5 "C) as die nie-fosfaatbevattende PU monsters (Tg begin onder -50°C).

Thesis (MSc)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: Biofouling in cooling water systems lead to several problems resulting in reduced efficiency and financial losses. Antifouling coatings present an environmental friendly solution to prevent biofouling alternatively to the current use of toxic chemicals in cooling water systems. In this study biofilm growth in a cooling water system was simulated in a modified flow cell system to evaluate industrial antifouling coatings and biocide-enriched coatings as potential antifouling coatings for metal surfaces. The design of a novel antifouling coating was also attempted. Firstly, analytical methods for biofilm monitoring to evaluate selected antifouling coatings and biocides were optimised. Pseudomonas sp. strain CT07 was selected to grow biofilms in the biofilm studies. A metal alloy of stainless steel and mild steel (3CR12) showed no corrosion after a 24 h biofilm growth and was selected as metal surface for the biofilm growth discs. Sonification for 5 min was determined as the optimum biofilm removal method from the growth discs. After biofilm removal the metal growth discs were stained with the LIVE/DEAD® BaclightTM Bacterial Viability kit. Visualisation by confocal laser scanning microscopy and flow cytometry revealed auto fluorescence signals from metal discs that hindered quantitative and qualitative analysis of the metal substrate. The use of Pseudomonas sp. strain CT07::gfp to grow biofilms on the metal growth discs and the exclusion of the stain SYTO9 from the LIVE/DEAD® BaclightTM Bacterial Viability kit reduced auto fluorescence signals from the metal discs. The industrial coatings containing quaternary ammonium salt (QAC), triclosan (TC) and copper oxide (CUO) respectively, showed the highest antimicrobial activity in the disc diffusion test. The minimum inhibition concentrations for silver nitrate (SN) and copper sulphate (CS) were 432 ppm and 160 ppm respectively. A minimum of 6.25 % of furanone solution (FR) was biocidal in the dilution susceptibility test. Secondly, the metal growth discs were coated respectively with the three selected industrial coatings QAC, TC and CUO and the epoxy biocide-enriched coatings SN, CS and FR and chemically characterised before and after exposure to biofilm formation. The antifouling activity of these coatings was also characterized. Growth media inoculated with Pseudomonas sp strain CT07::gfp was circulated through the modified flow cell system via a multichannel peristaltic pump for 48 h before the coated metal discs were removed and washed to perform chemical or antifouling analysis. All the industrial coatings and biocide enriched epoxy coatings complied with the thermal stability requirements of a cooling water system. Scanning electron microscopy (SEM) imaging and Energy dispersive X-ray spectroscopy (EDX) analysis confirmed that the adhesion properties of industrial coatings TC and QAC in aqueous environments were insufficient and that the copper and silver ions leached out of the biocide-enriched epoxy coatings. The qualitative analyses of the attachment of bacteria on the surfaces of both the industrial and biocide enriched epoxy coatings was confirmed by SEM, CLSM. The attached bacteria were removed and analysed quantitatively through plate counts and flow cytometry. None of the industrial coatings or the biocide incorporated epoxy coatings that were used in this study would therefore be efficient for the use on metal surfaces in cooling water systems. Thirdly, several approaches were followed to synthesise a poly(styrene-alt-maleic anhydride) (SMA) coating, chemically bind a furanone derivative, 2,5-dimethyl-4-hydroxy-3-(2H)-furanone, to the polymer back bone of the SMA coating for the application as an antifouling coating for cooling water systems. The synthesis of SMA was confirmed through 1H NMR and SEC and the synthesis of tert-butyl 2-(2-hydroxyethoxy) ethylcarbamate and 4-(2-(2-(tert-butoxycarbonyl)ethoxy)ethoxy)-4- oxobutanoic acid was confirmed through 1H NMR and ES-MS+. The synthesis of the end furanone derivative product could however not be achieved. / AFRIKAANSE OPSOMMING: Bio-aanpaksels in waterverkoelingsisteme veroorsaak talle probleme wat lei tot verminderde doeltreffendheid en finansiële verliese. Antimikrobiese oppervlakbedekkings verskaf ‘n omgewingsvriendelike oplossing om bio-aanpaksels te voorkom en ‘n alternatief vir die huidige gebruik van giftige chemikalieë in waterverkoelingsisteme. Biofilm groei in waterverkoelingsisteme was nageboots in ‘n gewysigde vloeiselsisteem om industriële aanpakwerende en biopsied bevattende antimikrobiese oppervlakbedekkings as potensiële aanpakwerende beskermingslae vir metaaloppervlaktes te evalueer. Die ontwerp van ‘n nuwe aanpakwerende beskermingslaag is ook ondersoek. Eerstens is analitiese moniteringsmetodes vir bio-aanpaksels op geselekteerde aanpakwerende antimikrobiese oppervlakbedekkings en biosiedes geoptimiseer. Pseudomonas sp. stam CT07 was verkies om bio-aanpaksels te simuleer gedurende hierdie studie. ‘n Metaalalooi van vlekvrye staal en sagte staal (3R12) het geen korrosie getoon na 24 uur se groei van bio-aanpaksels nie en is vir hierdie rede gebruik as metaal vir die bio-aanpaksel groeiplate. Dit was vasgestel dat sonifisering die optimale verwyderingsmetode vir groeiplate was. Na verwydering van bio-aanpaksels was die metaal groeiplate bedek met die LIVE/DEAD® BaclightTM bakteriële lewensvatbaarheid-toestel. Visualisering deur middel van konfokale mikroskopie en vloeisitrometrie het outofluoreserende seine vanaf die metaal groeiplate onthul wat kwantitatiewe en kwalitatiewe analise van die metaal substraat verhinder het. Die gebruik van Pseudomonas sp. stam CT07:gfp om bio-aanpaksels te kweek op metal plate en die uitsluiting van SYT09 van die LIVE/DEAD® BaclightTM bakteriële lewensvatbaarheid-toestel, het die outofluoreserende seine van die metaalskywe verminder. Industriële beskerminglae, wat onderskeidelik Kwaternêre ammonium sout (QAC), triclosan (TC) en koperoksied (CUO) bevat, het die hoogste antimikrobiese aktiwiteit in die skyf-diffusie toets getoon. Die minimum inhibisiekonsentrasies vir silwernitraat (SN) en kopersulfaat (CS) was onderskeidelik 432 dpm en 160 dpm. ‘n Minimum konsentrasie van 6.25% van die furanoonoplossing (FO) is geklassifiseer as ‘n biosied in die oplossingstoets.Tweedens was die metaal groei-skywe bedek met drie industriële beskermingslae QAC, TC en CUO en die epoksie-biosied-verrykte lae SN, CS en FR en chemiesgekarakteriseerd voor en na die vorming van bio-aanpaksel. Die karaktereienskappe van die aktiwiteit van die beskermingslae was ook vasgestel. Opgeloste triptiese soja sop vermeng met Pseudomonas sp strain CT07: gfp was gesirkuleer in die gemodifiseerde vloeisel deur ‘n multikanaal peristaltiese pomp vir 48 uur voordat die beskermde metaalskywe verwyder en gewas is om chemiese en aanpakwerende analise uit te voer. Al die industriële beskermingslae en biosied-verrykte epoksie-beskermingslae het aan die vereistes van termiese stabiliteit van ‘n waterverkoelingsisteem voldoen. Skandeer elektronmikroskopie (SEM) en X-straal spektroskopie (EDX) analise het aangetoon dat die aantrekkingseienskappe van industriële beskermingslae TC en QAC in waterige oplossings onvoldoende was en dat die koper- en silwerione uit die biosiedverrykte epoksie-resin beskermingslae diffundeer. Die kwalitatiewe analise van die aanpaksel van bakterieë op die oppervlaktes van beide industriële en biosied -verrykte epoksie-beskermingslae was bevestig deur SEM en CLSM. Die aangepakte bakterieë was verwyder en kwantitatief geanaliseer deur middel van plaattellings en vloeisitrometrie. Nie een van die industriële beskermingslae of die biosied-bevattende epoksie beskermingslae wat in hierdie studie gebruik is, is dus gepas vir gebruik op metaaloppervlaktes in waterverkoelingsisteme nie. Derdens was verskeie pogings aangewend om ‘n poli(stireen-alt-maleic anhidried) (SMA) beskermingslaag chemies te bind tot ‘n furanoon afgeleide 2.5-demitiel-4-hidroksie-3-(2H)- furanoon, tot die polimeer-ruggraat van die SMA beskermingslaag vir aanwending as ‘n aanpakwerende beskermingslaag vir waterverkoelingsisteme. Die sintese van SMA was bevestig deur 1H NMR en SEC en die sintese van tert-butyl 2-(2-hirdoksie-etoksie) etielkarbamaat en 4-(2- (2-(tert-butoksiekarboniel)etoksie)etoksie)-4-oksobutanoiesesuur was bevestig deur 1H NMR en ES-MS+. Die sintese van die uiteindelike afgeleide furanoon kon egter nie behaal word nie.

A major challenge facing widespread implementation of membrane-based water purification is fouling, which results in increased operating costs and reduced membrane lifetime. This thesis focuses on various methods, including novel membrane surface modifications and polymers that resist degradation when exposed to oxidizing agents used as disinfectants, to alleviate membrane fouling. Fouling-resistant ultrafiltration membrane coatings were prepared from poly(ethylene glycol) diglycidyl ether-crosslinked chitosan (chi-PEG hybrid). Composite membranes were prepared for oil-water emulsion filtration by coating the most promising chi-PEG hybrid onto a polysulfone ultrafiltration membrane. Optimization of the coating layer thickness led to composite membranes that exhibited water flux values more than 5 times higher than that of uncoated membranes after one day of oily-water crossflow filtration. The organic rejection of the coated membranes was also higher than that of the uncoated polysulfone membranes. Polydopamine (PDOPA) deposition was discovered to reduce fouling in water purification membranes. PDOPA was found to deposit from solution onto virtually any surface. When deposited on water purification membranes, PDOPA rendered the membrane more hydrophilic and less susceptible to fouling. Moreover, covalent binding of other molecules, such as amine-terminated poly (ethylene glycol) (PEG), to PDOPA is simple and performed using benign chemicals and conditions. Commercially-available polymeric membranes were modified with polydopamine, and all showed improved fouling resistance while filtering oil-water emulsions. To demonstrate the versatility and ease of PDOPA modification scalability, PDOPA was deposited on entire membrane modules, and the resulting modified module exhibited improved fouling resistance. Finally, high ion rejection, chlorine-tolerant sulfonated polysulfone thin-film composite membranes were prepared and characterized. Interestingly, freestanding thick sulfonated poly(arylene ether sulfone) (BPS) films exhibit nearly neutral electrostatic charge, even though sulfonation introduces fixed negative charge into the polymer structure. As a result, charge exclusion ion partitioning is not a dominant rejection mechanism in these films. However, composite membranes prepared from a BPS coating layer and a porous Udel polysulfone support exhibit a negatively charged surface and, presumably, charge exclusion would be a more important partitioning mechanism for these membranes. Therefore, thick BPS films do not exhibit certain drawbacks, such as reduced salt rejection of mixed-valence feeds, that are observed in BPS thin-film composite membranes. / text

No description available.

The possibility of using supercritical carbon dioxide (scCO2) as the primary solvent in a spray process for producing superhydrophobic surfaces have been examined in this work. Using scCO2 as solvent will have considerably lower environmental impact compared to an organic solvent since scCO2 is considered a green solvent as it is non-toxic, non-flammable and recyclable. To be able to work at the pressures needed to reach the supercritical state of carbon dioxide, a high-pressure technique called rapid expansion of supercritical solutions (RESS) has been used to produce the coatings. Fluorinated compounds are often used when producing superhydrophobic coatings due to their intrinsic water repellent properties, but generally these compound do not degrade in nature. Due to this, a wax and a biodegradable polymer have been used as the coating materials in this work. Two RESS set-ups were used to spray a polymer from solutions of scCO2 and acetone. The first system was based on a continuous flow of the solvent mixture and the polymer particles were collected on silica surfaces. Some of the coatings had superhydrophobic properties and the limitation with this technique was the loss of particles between the nozzle and the surface. In the second set-up, RESS was combined with electrostatic deposition (ED) to improve the particle collection. Different processing parameters were examined and most of the RESS-ED sprayed surfaces were superhydrophobic. This was demonstrated by high contact angles against water, low contact angle hysteresis and low tilt angles at which a water droplet rolls off the surface. It was also shown that the surface structures created when spraying using RESS-ED induced the important two-level roughness that was needed to achieve superhydrophobicity. A semi-continuous process for scaling-up the RESS system when spraying the wax has been developed. Temperature and pressure was investigated to find the highest solubility of the wax in scCO2, and 250 bar and 67 °C resulted in the largest amount of sprayed wax. It was also shown that the system is suitable for spray-coating the wax on different substrates such as glass, paper, aluminium etc. since all of these surfaces showed superhydrophobic properties. The wear resistance of the coatings were examined by different methods. Scratch resistance, vertical compression and the friction between the surface and a finger were analysed. The polymer coated surfaces showed a larger robustness compared with the wax surfaces in the scratch tests. The superhydrophobicity was lost for the wax coatings exposed to compression loads above 59 kPa and in the frictions test, one finger stroke over the coating destroyed the surface roughness. Finally, the wax surfaces were investigated as coating barriers to protect steel from corrosion. The superhydrophobic coating was stable up to 10 days before corrosion of the steel started. / <p>QC 20140922</p>

Multiscale (analytical and computational) models have been developed based on a thermodynamic variational principle (TVP) to model sintering and eventual mudcracking in thermal barrier coatings (TBCs) made using the electron beam physical vapour deposition (EB-PVD) process. It is assumed that the sintering occurs by interfacial diffusion at local contacts between columns and driven by changes in interface free energy and elastic stored energy of the coating. The models link diffusional processes at the scale of contacting feathery columns with the macroscopic deformation and sintering response. In service, the columns can come into contact and sinter together. As sintering progresses there is a build up of strain energy in the system which reduces the driving force for sintering and leads to either complete or incomplete sintering of the TBC depending on the magnitude of effective modulus (E) of the coating. By seeding the coating with initial imperfections, different types of behaviour are observed depending on the value of E and the spacing between imperfections. For compliant coatings, the response is insensitive to the presence of imperfections and the coating fully sinters. At higher values of E, strain energy is released by the development of intercolumnar cracks in the coating, which can propagate to the interface with the TGO (thermally grown oxide), deflect into the interface and propagate, leading to spallation of regions of the coating and loss of thermal protection. It is observed that cracks develop at initial imperfections in the structure. The greater the spacing between imperfections the faster the development of cracks at these locations. If a TBC contains a distribution of imperfections there is progressive formation of cracks, with the average spacing decreasing with time, after an initial incubation period. The crack density eventually saturates to a constant value, which depends on the mechanical properties of the TBC. Initially, a crack spacing, CS, in the range 1.5H ≤ CS ≤ 3H has been predicted based on trapezoidal contact models. Here H is the thickness of the coating. Crack spacing predicted using this model is consistent in the lower range of experimentally observed crack spacing. However, axisymmetric contact models predict a crack spacing, CS, in the range 4H ≤ CS ≤ 8H, which is in good agreement with experimentally observed crack spacing range 3H ≤ CS ≤ 10H reported in the literature. Compared to the trapezoidal contact models, axisymmetric contact models more accurately predict the sintering response.

Anionic chromate (VI) compounds are inhibitive pigments and have been effectively incorporated into organic coatings to protect metal surfaces from aggressive ions, but their risk as a human carcinogen and being harmful to the environment has led to the search of suitable alternatives. Aluminium alloy, AA2024-T3, is the substrate metal alloy used in the experiments and can be found in aircraft fuselage structures due to their high strength-to-weight ratio. However, the presence of intermetallic particles increases susceptibility to localised corrosion. To investigate the protection mechanisms of primers on light alloys, many different factors must be taken into account; from aluminium alloy corrosion processes, the effects of intermetallic additions to coating chemistry, morphology and inhibitive pigments. The chemical environment in which the samples are tested in will also affect the corrosion mechanisms of the alloy as well as the performance of the coatings and release of pigments. It will be important to consider which factors are operating under particular conditions so that experimental results can then be best interpreted. As part of this project, potentiodynamic polarisation, electrochemical impedance spectroscopy and electrochemical noise analysis have been used to investigate the protective mechanisms in which chromate-based paints protect against corrosion and UV-Visible spectroscopy, scanning acoustic microscopy and optical microscopy have been used to investigate pigment release mechanism to identify what characteristics are important when developing new primers.

Chloride, bromide, pyridinium and quinolinium homologues of 4-(N- hexadecylpyridinium-4-ylmethylidene-amino)-2,6-dichlorophenolate have been investigated in solution, Langmuir and Langmuir-Blodgett films. Techniques including spectroscopy, surface potential measurement, quartz crystal microbalance, surface plasmon resonance, atomic force microscopy, reectometry and X-ray diffraction have been used to characterise these molecular systems. In solution, solvatochroism was observed and Benisi-Hildebrand analysis revealed dimeric aggregation. Langmuir monolayers were compressed at the air/water interface and chromophore rotation was observed by surface potential measurement. Langmuir- Blodgett monolayers showed lm-thickness dependence on the deposition-pressure. Monolayer thicknesses between 6-24Ä were measured using SPR and molecular areas between 40-l25Ä2 were measured using a quartz crystal microbalance. Both the molecular/s/area)and monolayer thicknesses were deposition-pressure dependent. The high tilt phases were visually distinguishable from the low tilt phases using atomic force microscopy, The compounds showed phase behaviour that was predominantly alike for the bromide and chloride homologues but different for the pyridinium and quinolinum homologues. Multilayer Y-type films of the merocyanine dyes were analysed using reectometry and deposition-pressure dependent thicknesses were found. Alternate layer structures of NLO-active hemicyanine amphiphiles were used to achieve homogeneous. orientation ordering using active and inactive spacer layers. Ordering was achieved but the optical efficiency was reduced by high proportions of inactive material and interlayer dipole formation. Double chained hemicyanine molecules were used to form Z-type structures and subsequent layers were found to significantly interdigitate. Different chain lengths were found to interdigitate by the length of the shortest chain. Gas detection experiments were undertaken on the quinolinium, dichloro merocyanine using three optical geometries. The absorption method showed slow switching and poor sensitivity. The Kretschmann SPR geometry showed high sensitivity and rapid switching. The grating SPR geometry showed rapid switching but was less sensitive than the ATR method. Protonation of the monolayers was investigated using hydrochloric acid gas, acetic acid vapour and stearic acid immobilised within the lm.

The interest in superhydrophobic coatings have increased exponentially in the recentdecades due to their potential and versatility in their applications. The use forsuperhydrophobic surfaces range from water repellent fabric, to self cleaning surfacesand numerous applications in industry. In this project the durability of 6 differentsuperhydrophobic coatings have been examined. The durability was tested bydropping sand on the surfaces from a set hight of 10 cm and a flow of 40 g/min. Thesurfaces were mounted on a 45° angle. The surfaces were abraded for 30 seconds ata time and the static, receding, and advancing contact angles along with the roll-ofangle was measured. Five of the surfaces were built up with nano particles and onewas sand blasted and anodized to create a superhydrophobic structure. The surfacesthat withstood the most abrasion was the surface that had been calcined to improveadhesion and the surface that had been sand blasted and anodized. Measurementsshowed that the roll-off angle and the receding contact angle were the two bestindicators of the deterioration of a surface, while the static contact angle and theadvancing contact angle varied little with abrasion. The project was done at thecompany Technical Research Institute of Sweden (SP) at their chemistry, surfaces andmaterials department in Stockholm. All coatings and equipment was supplied by SP.

New restrictions and regulations regarding internal combustion engines introduced severe mechanical and thermo-mechanical loads on engine parts, mostly on piston rings, leading to high wear and premature damage, thus causing oil leakage into the combustion chamber and increasing emissions. One of the most viable solutions to overcome these issues is the use of coatings to change surface properties. Coatings produced by High Power Impulse Magnetron Sputtering (HiPIMS) and Direct Current Magnetron Sputtering (dcMS) have shown promising results to form dense coatings with high hardness and high wear resistance. Those properties can be further enhanced by using a periodic structure in the form of multilayers of different materials. In this study, we proposed a hybrid process with HiPIMS and dcMS to produce multilayer coatings of CrN and CrAlN. Different target combinations and negative substrate bias were studied. Furthermore, the base layer influence and an evaluation of the periodicity effects were presented. Structure and morphology of the coatings were characterized with X-Ray Diffraction, Scanning Electron Microscopy and Atomic Force Microscopy. Meanwhile, instrumented nanohardness, corrosion and wear tests were performed to characterize mechanical, electrochemical and tribological properties. Results showed that the choice of target combination and bias values are fundamental for enhancing mechanical and tribological properties. On the other hand, we found no evidence of superlattice hardening when changing periodicity but an increase in corrosion resistance when reducing periodicity was found. The combination of targets, substrate bias, base layer and periodicity presented here showed promising results on wear tests, especially when compared with the current coating under the same engine conditions. / Novas restrições e regulamentações de motores de combustão interna introduziram severas cargas mecânicas e termomecânicas no motor, principalmente nos anéis de pistão, o que leva a um alto desgaste e ao dano prematuro dos mesmos e causa vazamentos de óleo na câmara, aumentando as emissões de poluentes. Uma das soluções mais viáveis para solucionar este problema é o uso de recobrimentos para alterar as propriedades da superfície. Recobrimentos produzidos pelas técnicas High Power Impulse Magnetron Sputtering (HiPIMS) e Direct Current Magnetron Sputtering (dcMS) mostraram resultados promissores na formação de filmes densos com elevada dureza e resistência ao desgaste. Essas propriedades podem ser melhoradas com a utilização de estruturas periódicas na forma de multicamadas. Nesse estudo, foi proposto um processo híbrido de HiPIMS e dcMS para produzir recobrimentos multicamadas de CrN/CrAlN. Diferentes combinações de alvos e de valores de polarização negativa do substrato (bias) foram estudadas. Além disso, foram apresentadas a influência da camada base e a avaliação dos efeitos da mudança de periodicidade. Estrutura e morfologia dos recobrimentos foram caracterizadas por Difração de Raios-X, Microscopia Eletrônica de Varredura e Microscopia de Força Atômica. As caracterizações mecânica, eletroquímica e tribológica foram realizadas com ensaios de Nanodureza Instrumentada, Corrosão e Desgaste. Os resultados mostram que a escolha da combinação de alvos e de valores de bias são fundamentais para a melhoria das propriedades mecânicas e tribológicas. Por outro lado, não foram encontradas evidências de endurecimento devido ao efeito de super-redes com a variação de periodicidade, mas um aumento da resistência à corrosão foi evidenciado. A combinação de alvos, bias, camada base e periodicidade apresentadas aqui mostraram resultados promissores em testes de desgaste, principalmente quando comparadas com os recobrimentos utilizados comercialmente nas mesmas condições de trabalho do motor.