BUSCADOR RECOLECTA

Anti-icing or passive strategies have undergone a remarkable growth in importance as a complement for the de-icing approaches or active methods. As a result, many efforts for developing icephobic surfaces have been mostly dedicated to apply superhydrophobic coatings. Recently, a different type of ice-repellent structure based on slippery liquid-infused porous surfaces (SLIPS) has attracted increasing attention for being a simple and effective passive ice protection in a wide range of application areas, especially for the prevention of ice formation on aircrafts. In this work, the electrospinning technique has been used for the deposition of PVDF-HFP coatings on samples of the aeronautical alloy AA7075 by using a thickness control system based on the identification of the proper combination of process parameters such as the flow rate and applied voltage. In addition, the influence of the experimental conditions on the nanofiber properties is evaluated in terms of surface morphology, wettability, corrosion resistance, and optical transmittance. The experimental results showed an improvement in the micro/nanoscale structure, which optimizes the superhydro-phobic and anticorrosive behavior due to the air trapped inside the nanotextured surface. In addi-tion, once the best coating was selected, centrifugal ice adhesion tests (CAT) were carried out for two types of icing conditions (glaze and rime) simulated in an ice wind tunnel (IWT) on both as-deposited and liquid-infused coatings (SLIPs). The liquid-infused coatings showed a low water adhesion (low contact angle hysteresis) and low ice adhesion strength, reducing the ice adhesion four times with respect to PTFE (a well-known low-ice-adhesion material used as a reference)., Project RTI2018-096262-B-C41-MAITAI, funded by MCIN/AEI/10.13039/501100011033 and by ERDF 'A way of making Europe'. Grant PRE2019-090656: funded by MCIN/AEI/10.13039/501100011033 and by ESF 'Investing in your future'. Project PJUPNA1929 funded by MCIN/AEI/10.13039/501100011033 and by ERDF 'A way of making Europe' and by BEI.

Among the various polymeric options employed for the deposition of electrospun coat-ings, poly(vinylidene fluoride) (PVDF) has been widely investigated thanks to its excellent mechanical properties, high chemical resistance, and good thermal stability. In this work, the electrospin-ning technique is used for the fabrication of functional PVDF fibers in order to identify and evaluate the influence of the experimental conditions on the nanofiber properties in terms of optical trans-mittance, wettability, corrosion resistance, and surface morphology. Some of these properties can play a relevant role in the prevention of ice formation in aircrafts. According to this, a matrix of 4 × 4 samples of aluminum alloy AA 6061T6 was successfully coated by controlling two operational input parameters such as the resultant applied voltage (from 10 up to 17.5 KV) and the flow rate (from 800 up to 1400 µL/h) for a fixed polymeric precursor concentration (15 wt.%). The experimental results have shown a multilevel fiber-bead structure where the formation of a fiber mesh directly depends on the selected operational parameters. Several microscopy and surface analysis techniques such as confocal microscopy (CM), field emission scanning electron microscopy (FE-SEM), UV/vis spectroscopy, and water contact angle (WCA) were carried out in order to corroborate the morphology, transmittance, and hydrophobicity of the electrospun fiber composite. Finally, the corrosion behavior was also evaluated by electrochemical tests (Tafel curves measurement), show-ing that the presence of electrospun PVDF fibers produces a relevant improvement in the resultant corrosion resistance of the coated aluminum alloys. © 2021 by the authors. Licensee MDPI, Basel, Switzerland., This research was funded by the Spanish ministry of science and innovation (Project RTI2018-096262-B-C41-MAITAI, Multidisciplinary Approach for the Implementation of new Technologies to prevent Accretion of Ice on aircraft), and by the Public University of Navarre (Project PJUPNA1929).

The development of surface engineering techniques to tune-up the composition,
structure, and function of materials surfaces is a permanent challenge for the scientific
community. In this chapter, the electrospinning process is proposed as a versatile
technique for the development of highly hydrophobic or even superhydrophobic
surfaces. Electrospinning makes possible the fabrication of nanostructured ultrathin
fibers, denoted as electrospun nanofibers (ENFs), from a wide range of polymeric
materials that can be deposited on any type of surface with arbitrary geometry.
In addition, by tuning the deposition parameters (mostly applied voltage, flow rate,
and distance between collector/needle) in combination with the chemical structure
of the polymeric precursor (functional groups with hydrophobic behavior) and its
resultant viscosity, it is possible to obtain nanofibers with highly porous surface. As a
result, functionalized surfaces with water-repellent behavior can be implemented in
a wide variety of industrial applications such as in corrosion resistance, high efficient
water-oil separation, surgical meshes in biomedical applications, or even in energy
systems for long-term efficiency of dye-sensitized solar cells, among others., This work was supported by the Ministerio de Ciencia, Innovación y Universidades-Retos (Project RTI2018-096262-B-C41-MAITAI) and by the Public
University of Navarre (Project PJUPNA1929).
info:eu-repo/grantAgreement/AEI/Plan Estatal de Investigación Científica y Técnica y de Innovación 2017-2020/RTI2018-096262-B-C41

A superhydrophobic composite coating consisting of polytetrafluoroethylene (PTFE) and poly(acrylic acid)+ β-cyclodextrin (PAA + β-CD) was prepared on an aluminum alloy AA 6061T6 substrate by a three-step process of electrospinnig, spin coating, and electrospraying. The electrospinning technique is used for the fabrication of a polymeric binder layer synthesized from PAA + β-CD. The superhydrophilic characteristic of the electrospun PAA + β-CD layer makes it suitable for the absorption of an aqueous suspension with PTFE particles in a spin-coating process, obtaining a hydrophobic behavior. Then, the electrospraying of a modified PTFE dispersion forms a layer of distributed PTFE particles, in which a strong bonding of the particles with each other and with the PTFE particles fixed in the PAA + β-CD fiber matrix results in a remarkable improvement of the particles adhesion to the substrate by different heat treatments. The experimental results corroborate the important role of obtaining hierarchical micro/nano multilevel structures for the optimization of superhydrophobic surfaces, leading to water contact angles above 170°, very low contact angle of hysteresis (CAH = 2°) and roll-off angle (αroll−off
< 5°). In addition, a superior corrosion resistance is obtained, generating a barrier to retain the electrolyte infiltration. This study may provide useful insights for a wide range of applications., Project RTI2018-096262-B-C41–MAITAI, funded by MCIN/AEI/10.13039/501100011033 and by ERDF “A way of making Europe”. Grant PRE2019-090656: funded by MCIN/AEI/10.13039/501100011033 and by ESF “Investing in your future”. Project PJUPNA1929 funded by MCIN/AEI/10.13039/501100011033 and by ERDF “A way of making Europe” and by BEI.

In this work, a one-step electrospinning technique has been implemented for the design and development of functional surfaces with a desired morphology in terms of wettability and corrosion resistance by using polycaprolactone (PCL) and zinc oxide nanoparticles (ZnO NPs). The surface morphology has been characterized by confocal microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM) and water contact angle (WCA), whereas the corrosion resistance has been evaluated by Tafel polarization curves. Strict control over the input operational parameters (applied voltage, feeding rate, distance tip to collector), PCL solution concentration and amount of ZnO NPs have been analyzed in depth by showing their key role in the final surface properties. With this goal in mind, a design of experiment (DoE) has been performed in order to evaluate the optimal coating morphology in terms of fiber diameter, surface roughness (Ra), water contact angle (WCA) and corrosion rate. It has been demonstrated that the solution concentration has a significant effect on the resultant electrospun structure obtained on the collector with the formation of beaded fibers with a higher WCA value in comparison with uniform bead-free fibers (dry polymer deposition or fiber-merging aspect). In addition, the presence of ZnO NPs distributed within the electrospun fibers also plays a key role in corrosion resistance, although it also leads to a decrease in the WCA. Finally, this is the first time that an exhaustive analysis by using DoE has been evaluated for PCL/ZnO electrospun fibers with the aim to optimize the surface morphology with the better performance in terms of corrosion resistance and wettability., Project RTI2018-096262-B-C41–MAITAI, funded by MCIN/AEI/10.13039/501100011033 and, as appropriate, by ERDF 'A way of making Europe'. Grant PRE2019-090656, funded by MCIN/AEI/10.13039/501100011033 and, as appropriate, by ESF 'Investing in your future'. Project PJUPNA1929 funded by MCIN/AEI/10.13039/501100011033 and, as appropriate, by ERDF 'A way of making Europe' and by BEI.

La formación y acumulación de hielo supone un riesgo en la seguridad de los aviones durante todas las fases de vuelo, especialmente cuando la aeronave se encuentre a media-baja altitud y su velocidad sea lenta (despegue-ascenso y aproximación-aterrizaje). Actualmente, la mayoría de las aeronaves poseen sistemas activos de deshielo y/o anti hielo. Sin embargo, las condiciones severas conducirán a que tarde o temprano se produzca hielo en este tipo de sistemas. Por lo que será necesario la combinación de estrategias pasivas y activas para prevenir la formación de hielo y su posterior eliminación. De esta forma, los sistemas pasivos como el desarrollo de recubrimiento hielofóbicos contribuirán a un menor consumo de energía en los activos. En este estudio, se han desarrollado recubrimientos hielofóbicos a través de una estrategia novedosa basada en superficies compuestas por fibras o partículas con polímeros de baja energía superficial. Tanto la distribución de fibras aleatorias como la coalescencia de partículas dan lugar a estructuras multinivel a micro y nanoescala que son propicias para la optimización de superficies superhidrofóbicas. Estas estructuras contribuirán a reducir la mojabilidad de las gotas de agua (α > 150°) y obtener una alta movilidad, claves para prevenir la formación de hielo (anti-hielo). A su vez, estas superficies actuarán como una barrera protectora frente a la corrosión en aleaciones metálicas de uso aeronáutico. Por un lado, reduciendo la interación de la superficie con el agente corrosivo y por el otro lado, encapsulando inhibidores de corrosion en las fibras, como por ejemplo óxidos metálicos (ZnO NPs). No obstante, las condiciones severas provocarán la formación hielo debido a la aparición de microgotas dentro de las cavidades de la estructura rugosa, que originarán la nucleación del hielo. Una vez formado el hielo, las superficies presentarán una alta adhesión al hielo (65 kPa), generado por el anclaje o entrelazamiento de la capa de hielo con las texturas de la superficie y que ocasionarán la delaminación de la superficie debido al fallo cohesivo de las fibras tras varios ciclos del ensayo de adhesión al hielo. Por esta razón, las superficies superhidrofóbicas en la medida en que retrasen o eviten la nucleación del hielo en las cavidades de su estructura, contribuirán a un mejor rendimiento anti-hielo y a una menor adhesión al hielo (mejorando el deshielo). Por ello, con el fin de optimizar el comportamiento hielofóbico, estas superficies fibrosas serán idales para el desarrollo de superficies porosas impregnadas de líquidos deslizantes, conocidas como SLIPS. Para ello, la capa de aire atrapada entre las texturas de la superficie y las gotas de agua, es sustituida por un lubricante a base de líquidos orgánicos y con baja energía superficial. Esta interfaz provocará una alta movilidad de las gotas (α < 10°) y que la nucleación se vea desfavorecida, lo que contribuye al retaso de la congelación y una ultra baja adhesión al hielo (4,5 kPa). Sin embargo, tras varios ciclos sin infusionar, la adhesión al hielo se verá incrementada (30 kPa) ocasionada por la pérdida de la capa lubricante y que a su vez ocasionará delaminaciones del material por la nucleación del hielo en las cavidades. Por esta razón, las propiedades hielofóbicas de estas superficies dependenrán de la capacidad de retener el lubricante, así como una buena afinidad y estabilidad química del lubricante con las fibras. Para la fabricación de las fibras se ha utilizado la técnica de electrospinning, donde se ha aplicado un diseño de experimentos (DoE) con el fin de comprender la relación entre los parámetros de entrada y salida del sistema, así como construir un modelo extrapolable a otros sistemas de polímeros que permita su optimización respecto a la morfología superficial, ángulo de contacto con el agua (WCA) y velocidad de corrosión. Ademas, se ha utilizado la técnica de electrospinning en combinación con otras técnicas (spin coating y electrospraying) para la obtención de superficies con estructuras basadas en coalescencia de partículas y que, además, doten de una buena adherencia al sustrato tras diferentes tratamientos térmicos. Por último, se han obtenido fibras compuestas por nanopartículas de polímeros no electrospineables, dando lugar a fibras de nuevos materiales. Para caracterizar el rendimiento hielofóbico de las superficies desarrolladas, se han utilizado diferentes metodologías, que han permitido analizar la adhesión al hielo, así como la cantidad de hielo acumulado en función de sus condiciones de formación y comparar su rendimiento respecto a diferentes materiales repelentes al hielo, incluyendo soluciones comerciales y tendencias actuales. Para ello, se han reproducido las condiciones reales de formación de hielo en vuelo mediante un túnel de hielo, obteniendo tanto hielo claro como granulado, así como ensayar el fenómeno de runback o hielo secundario. Finalmente, se ha realizado un estudio comparativo de la adhesión al hielo mediante hielo estático fomado en molde, utilizando diferentes intalaciones del ensayo de adhesión y suponiendo un paso hacia la estandarización de las propiedades hielofóbicas de los recubrimientos diseñados a lo largo de esta Tesis., The formation and accreation of ice is a safety risk for aircraft during all phases of flight, especially when the aircraft is at medium-low altitude and flying at low speeds (take off-ascent and approach-landing). Currently, most aircraft are equipped with active de-icing and/or anti-icing systems. However, severe conditions will inevitably lead to ice formation in these systems. Therefore, a combination of passive and active strategies will be necessary to prevent ice formation and its subsequent removal. In this way, passive systems such as the development of icephobic coatings will contribute to lower energy consumption in active systems. In this study, icephobic coatings have been developed through a novel strategy based on surfaces composed of fibres or particles with low surface energy polymers. Both random fibre distribution and particle coalescence result in micro/nano level structures that are suitable for the optimisation of superhydrophobic surfaces. These structures will contribute to reduce the wettability of water droplets and achieve high mobility (α < 5°), key to prevent ice formation (anti-icing). In addition, these surfaces will act as a protective barrier against corrosion in aerospace metallic alloys. On the one hand, by reducing the surface interaction with the corrosive agent and on the other hand, by encapsulating corrosion inhibitors such as metal oxides (ZnO NPs) in the fibres. Nevertheless, severe conditions will lead to ice formation due to the presence of micro droplets within the cavities of the rough structure, creating ice nucleation. Once ice has formed, the surfaces will exhibit high ice adhesion (65 kPa), generated by the anchorage or interlocking of the ice layer with the surface textures. This will result in Surface delamination due to the cohesive failure of the fibers after multiple ice adhesion test cycles. For this reason, the superhydrophobic surfaces that delay or prevent ice nucleation within the cavities of their structures, will provide a better anti-icing performance and reduced ice adhesion (improved de-icing). Therefore, in order to optimize the icephobic behavior, these fibrous surfaces are ideal for the development of porous surfaces infused with slippery liquids, known as SLIPS. Where the layer of air trapped between the surface textures and water droplets is replaced by a lubricant based on organic liquids with low surface energy. This interface results in high droplet mobility (α < 10°) and hinders nucleation, contributing to delay freezing and ultra-low ice adhesion (4.5 kPa). However, after several cycles without re-infusion, the ice adhesion will increase (30 kPa) due to the loss of the lubricant layer and leading to material delamination caused by ice nucleation in the cavities. For this reason, the icephobic properties of these surfaces will depend on the ability to retain the lubricant, as well as a good affinity and chemical stability of the lubricant with the fibres. The electrospinning technique has been used to fabricate the fibres, where a design of experiments (DoE) was applied to understand the relationship between the input and output parameters of the system, as well as to create a model that can be extrapolated to other polymer systems, in order to optimize the surface morphology, water contact angle (WCA) and corrosion rate. Furthermore, the electrospinning technique has been used in combination with spin coating and electrospraying techniques to obtain surfaces with structures based on particle coalescence while ensuring good substrate adhesion after various heat treatments. In addition, fibers composed of non-electrospinnable polymer nanoparticles have been obtained, resulting in fibers of new materials for the first time. In order to characterize the icephobic performance of the developed surfaces, various methodologies have been used to analyze ice adhesion and the amount of ice acreation under different icing conditions and to compare their performance with different antiicing materials, including commercial solutions and current trends. For this purpose, real icing conditions in flight have been reproduced within an icing wind tunnel, generating both glaze and rime ice, as well as testing the running wet icing mechanisms and direct impingement of supercooled droplets. Finally, the ice adhesion has been studied and compared using static ice formed in mould, using different ice adhesion test facilities and representing a step forward in the standarization efforts of icephobic surfaces designed along this Thesis., This work was supported by the Project RTI2018-096262-B-C41 MAITAI, funded by MCIN/AEI/10.13039/501100011033 and by ERDF ‘A way of making Europe’. Grant PRE2019-090656: funded by MCIN/AEI/10.13039/501100011033 and by ESF ‘Investing in your future’. Project PJUPNA1929 funded by MCIN/AEI/10.13039/ 501100011033 and by ERDF ‘A way of making Europe’ and by BEI. Grant Erasmus+ funded by European Union and Campus iberus., Programa de Doctorado en Ciencias y Tecnologías Industriales (RD 99/2011), Industria Zientzietako eta Teknologietako Doktoretza Programa (ED 99/2011)

A superhydrophobic composite coating consisting of polytetrafluoroethylene (PTFE) and poly(acrylic acid)+ β-cyclodextrin (PAA + β-CD) was prepared on an aluminum alloy AA 6061T6 substrate by a three-step process of electrospinnig, spin coating, and electrospraying. The electrospinning technique is used for the fabrication of a polymeric binder layer synthesized from PAA + β-CD. The superhydrophilic characteristic of the electrospun PAA + β-CD layer makes it suitable for the absorption of an aqueous suspension with PTFE particles in a spin-coating process, obtaining a hydrophobic behavior. Then, the electrospraying of a modified PTFE dispersion forms a layer of distributed PTFE particles, in which a strong bonding of the particles with each other and with the PTFE particles fixed in the PAA + β-CD fiber matrix results in a remarkable improvement of the particles adhesion to the substrate by different heat treatments. The experimental results corroborate the important role of obtaining hierarchical micro/nano multilevel structures for the optimization of superhydrophobic surfaces, leading to water contact angles above 170°, very low contact angle of hysteresis (CAH = 2°) and roll-off angle (αroll−off
< 5°). In addition, a superior corrosion resistance is obtained, generating a barrier to retain the electrolyte infiltration. This study may provide useful insights for a wide range of applications, Funding: Project RTI2018-096262-B-C41–MAITAI, funded by MCIN/AEI/10.13039/501100011033 and by ERDF “A way of making Europe”. Grant PRE2019-090656: funded by MCIN/AEI/10.13039/501100011033 and by ESF “Investing in your future”. Project PJUPNA1929 funded by MCIN/AEI/10.13039/501100011033 and by ERDF “A way of making Europe” and by BEI. The authors would like to express their grateful acknowledgement for the support received from the Asociación de la Industria Navarra (AIN). In addition, F.J.P acknowledges financial support from Grant PID2021-126169OB-100 funded by MCIN/AEI/10.12039/501100011033 and by “A way of making Europe”., Peerreview