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Heat exchangers are essential to optimize the efficiency of Thermoelectric Generators (TEGs), and heat pipes without fans have proven to be an advantageous design as it maintains the characteristic robustness of thermoelectricity, low maintenance and lack of moving parts. However, the efficiency of these heat exchangers decreases under natural convection conditions, reducing their heat transfer capacity and thus thermoelectric power production. This work reports on a novel heat exchanger that combines for the first time, phase change and radiative cooling in a thermoelectric generator to improve its efficiency and increase the production of electrical energy, specially under natural convection. For this, two thermoelectric generators with heat-pipes on their cold sides have been tested: one with the radiative coating and the other without it. Their thermal resistances have been determined and the electric power output was compared under different working conditions, namely, natural convection and forced convection indoors and outdoors. The experimental tests show a clear reduction of the heat exchanger thermal resistance thanks to the radiative coating and consequently, an increase of electric production 8.3 % with outdoor wind velocities of 1 m/s, and up to 54.8 % under free convection conditions. The application of the radiative surface treatment is shown to result in a more stable electrical energy production, suppressing the drastic decrease in the generated electric power that occurs in thermoelectric generators when they work under free convection. The authors acknowledge the support of the Spanish Ministry of Science, Innovation and Universities, and the European Regional Development Fund , under grants PID2021-124014OB-I00 (VIVOTEG), TED2021-129359B-I00 (GEOTEG), PGC2018-101743-B-I00 (SIP) and RTI2018-093921-A-C44 (SMOOTH). Open access funding provided by Universidad Pública de Navarra.

This work describes the fabrication process of moth eye antireflective poly (methyl methacrylate) transparent films via roll to roll thermal nanoimprint lithography. The process parameters are investigated and adjusted in order to obtain from a single moth-eye structured mold, a range of antireflective topographies that gradually vary their geometry from protruding to intruding nanocones. A correlation between the process parameters with the optical and mechanical properties of the films is established to illustrate the influence of the processing parameters and serve as guideline to produce antireflective flexible films with balanced properties and optimized performance adequate to the application environment. A finite element model is described predicting the mechanical behavior of the moth-eye PMMA imprinted nanostructures.

12 pages, 8 figures, 1 table.-- Data availability: Data will be made available on request, Subpolar coastal waters are key hotspots in the global carbon cycle. However, the small-scale distribution of partial pressure of carbon dioxide (pCO2) in these environments and the physical and biological controls underlying this variability are still poorly understood. Here, we examine simultaneous high-resolution spatial measurements of wind speed and pCO2, temperature, salinity, and in-vivo chlorophyll-a fluorescence (chl-a fluo, a proxy of phytoplankton biomass) in surface waters that were obtained during an oceanographic survey in the Argentinian Beagle Channel (subantarctic Atlantic Patagonian) in early fall 2017. The 240 km study transect (centered at 55°S - 67°W) was divided into two zones: (A1) The Beagle Channel innermost portion, semi-enclosed and subject to strong continental influence and (A2) its eastern outlet towards the open Southwest Atlantic. Discrete seawater samples were also collected for apparent oxygen utilization (AOU), nutrients and pH measurements. High-resolution spatial measurements revealed the persistence of pCO2 below atmospheric equilibrium, increasing in median (interquartile range 25–75%) from 314 μatm in the inner Beagle Channel (A1) to 348 μatm towards the adjacent open sea (A2). A decrease in atmospheric CO2 sequestration was associated with an increase in water temperature from 9.5 °C to 10.7 °C, salinity from 30.8 to 32.5, and chl-a fluo from 2.24 to 2.91 mg m−3 along the coastal-offshore gradient. Low AOU and nutrient levels were found in regions inside the channel. Indeed, the relationships between CO2 and temperature or salinity were significantly different from those expected from the theoretical solubility effect, indicating a dominance of metabolic over physicochemical controls on this gas. Moreover, physical factors such as vertical stratification contributed to the variable surface pCO2 values. These findings reveal the existence of short-scale spatial variability of CO2 in the Beagle Channel, improving our understanding of the multiple controls on atmospheric carbon sequestration in extensive subpolar continental shelves, We acknowledge support from the Spanish Government through grants CTM2014-56987-P (VA-DE-RETRO Project) and RTI2018-100844-B-C33 (SAGA project) and also recognize the institutional support of the Spanish Government through the Severo Ochoa Centre of Excellence accreditation (CEX2019-000928-S). This study was funded by grants from the Council for Research and Scientific Development of Brazil (CNPq, 203366/2019-0, 314995/2020-0) and the Research Support Foundation of the State of Rio de Janeiro (E-26/211.329/2021 and E-26/201.118/2022). H.M. and L.C.C. were awarded by CNPq Research Productivity and FAPERJ Scientist of Our State fellowships. L.C.C. was awarded by UERJ/PROCIENCIA fellowship

Nanostructured surfaces, giving rise to unique physical phenomena, can bestow materials with a number of advanced functionalities. The design of such surfaces is frequently bio-inspired and provides with functionalities such as superhydrophobicity, self-cleaning, dry adhesion, antibacterial or, as presented in this thesis, antireflection inspired from the moth´s eyes. A practical, low-cost, versatile, and easy-scalable approach for the fabrication of functional micro/nanostructures is nanoimprint lithography (NIL) on polymeric materials. This process involves transferring nano or micro patterns from a mold to a thermoplastic film in the case of thermal NIL (T-NIL), or to a UV-cross-linkable photoresin in the case of UV-NIL, by mechanical deformation. The process is scalable via roll-to-roll (R2R) nanoimprint technology, where the mold is incorporated in a roller to carry out a continuous imprint process. This thesis is focused on the development of the NIL process to fabricate moth-eye inspired antireflective (AR) nanostructures, and its scaling up employing R2R NIL technology. Moth-eye AR nanopatterns, consisting of hexagonal arrays of nanocones with dimensions of about 250 nm, will be particularly useful as light trapping structures in photovoltaic devices, or to reduce reflections in screens or optical components. The major concern for the practical application of these surfaces is their poor mechanical resistance and their short-term durability when exposed to outside environmental conditions of UV radiation, humidity, and temperature, leading to the fast degradation of the polymeric matrix and therefore of the surface functionality. As such, this thesis also aims to improve the moth-eye AR surfaces physical and chemical resistance to allow for their use in real applications. Towards this aim, in the first part of the thesis, addition of titanium dioxide (TiO2 or titania) nanoparticles as reinforcing elements of the moth-eye AR topography made of polymethyl methacrylate (PMMA) is studied. Highly transparent PMMA/TiO2 surface nanocomposites using T-NIL are prepared by incorporating to the surface well-dispersed colloidal titania, and the impact of the nanofillers on the mechanical and thermal properties is investigated. Being TiO2 a wide band gap semiconductor and an efficient photocatalyst, its incorporation onto the surface also provides for additional functionalities such as photo-induced hydrophilicity and self-cleaning behavior. An additional approach studied to improve the performance of the material is the coating of the AR topography with a thin film of sputtered titania. The coating, while preserving the antireflective properties, protects the nanostructures against mechanical damage and improves substantially their thermal stability. Likewise, the titania coated AR surfaces shows photo-induced self-cleaning properties.In the direction of improving durability, a more weather resistant polymer such as the fluoropolymer poly (vinylidene fluoride) (PVDF) is investigated replacing the PMMA as nanocomposite matrix, whereby further improvement on durability and weathering resistance is demonstrated. In the second part of the thesis, the fabrication process of AR nanostructured surfaces scaled up by roll-to-roll NIL processing is developed, increasing significantly the fabrication throughput. The influence of the processing parameters on the imprinted AR features and its final functional performance is studied and adjusted in order to improve the mechanical stability concomitantly with the optical performance. Finally, roll-to-roll NIL processing is also applied to produce other functional surfaces, such as Fresnel lenses for micro-concentrator photovoltaic applications, in this case using the UV-NIL approach. Further to imprinting arrays of Fresnel microlenses, a double UV-NIL process is developed to incorporate the moth-eye AR topography on the reverse side of the Fresnel array. The concentration efficiency of these lenses is improved by reducing the reflection losses. In summary, this thesis describes the development of multifunctional antireflective surfaces based on the moth-eye polymer nanostructures reinforced with active nanofillers to achieve improved mechanical, thermal, and weathering properties, showing in addition photo-induced self-cleaning functionalities. The fabrication of the AR surfaces and Fresnel microlenses using the mass production roll-to-roll NIL manufacturing is demonstrated and therefore, the validity of the processing technology for the use of structured functional surfaces in real applications is substantiated. La nanoestructuración de superficies da lugar a fenómenos físicos únicos que pueden conferir a los materiales una serie de funcionalidades avanzadas adicionales a las que ya poseen. El diseño de estas superficies se inspira frecuentemente en la naturaleza y proporciona funcionalidades como superhidrofobicidad, autolimpieza, adhesión en seco, propiedades antibacterianas, o, como se presenta en esta tesis, propiedades antirreflectantes inspiradas en los ojos de las polillas. La técnica de litografía por nanoimpresión (nanoimprint lithography o NIL) constituye un enfoque práctico, económico, versátil y fácilmente escalable para la fabricación de micro o nanoestructuras en polímeros. Este proceso implica la transferencia del patrón micro o nanométrico mediante deformación mecánica desde un molde a una película de material termoplástico en el caso del proceso de NIL térmico (T-NIL) o a una resina curable con luz UV en el caso de la variante UV-NIL. Estos procesos son escalables mediante tecnología rollo a rollo (roll-to-roll o R2R), donde el molde se incorpora en un rodillo para llevar a cabo un proceso continuo de impresión. La presente tesis doctoral se centra en la puesta a punto de la fabricación mediante NIL de superficies antirreflectantes (AR) inspiradas en el ojo de la polilla, y en su escalado utilizando la tecnología de nanoimpresión R2R. Las topografías antirreflectantes consisten en nanoconos ordenados hexagonalmente con dimensiones de alrededor de 250 nm. Estas superficies son particularmente útiles como estructuras captadoras de luz en dispositivos fotovoltaicos, o para reducir reflexiones de la luz en pantallas o componentes ópticos. El mayor obstáculo para la aplicación práctica de estas superficies funcionales es su escasa resistencia mecánica y durabilidad bajo condiciones ambientales de radiación UV, humedad, y temperatura, que conducen a una rápida degradación de la matriz polimérica y de las funcionalidades superficiales. Por lo tanto, otro objetivo importante de esta tesis es también mejorar la resistencia física y química de las superficies AR nanoestructuradas para permitir su uso en aplicaciones reales. Con este objetivo, en la primera parte de esta tesis se estudia la adición de nanopartículas de dióxido de titanio (TiO2 o titania) como elemento de refuerzo de las topografías AR inspiradas en el ojo de la polilla fabricadas en polimetilmetacrilato (PMMA). Se fabrican superficies nanocompuestas altamente transparentes de PMMA/TiO2 utilizando T-NIL, mediante la incorporación de titania coloidal homogéneamente dispersada en la superficie, y se investiga el impacto de los nanorefuerzos en las propiedades mecánicas y térmicas. Al ser el TiO2 un semiconductor de banda ancha y un fotocatalizador eficiente, su incorporación a la superficie también proporciona funcionalidades adicionales como hidrofilicidad fotoinducida y capacidades de autolimpieza. El recubrimiento de la topografía AR con una película delgada de titania pulverizada se estudia como enfoque adicional. El revestimiento, al tiempo que conserva las propiedades antirreflectantes, protege las nanoestructuras contra daños mecánicos y mejora sustancialmente su estabilidad térmica. Asimismo, las superficies AR recubiertas de titania muestran propiedades de autolimpieza fotoinducidas. Con la finalidad de mejorar la durabilidad, se propone un polímero fluorado más resistente a la intemperie como es el poli (fluoruro de vinilideno) (PVDF) como reemplazo del PMMA, demostrando una mayor resistencia a la intemperie y durabilidad. En la segunda parte de la tesis, se desarrolla el proceso de escalado de la fabricación de superficies AR nanoestructuradas mediante tecnología de nanoimpresión R2R, lo que permite incrementar significativamente el rendimiento de la fabricación. Se estudia la influencia de los parámetros de procesado en las características de la nanotopografía AR impresa así como en el rendimiento funcional final, y se ajustan para mejorar la estabilidad mecánica en concordancia con el rendimiento óptico. Finalmente, el procesado de nanoimpresión R2R se emplea también para la fabricación de lentes de Fresnel utilizadas en sistemas de micro concentración fotovoltaica, en este caso utilizando la variante de UV-NIL. Además de la impresión de matrices de estas microlentes de concentración, también se desarrolla un proceso de doble UV-NIL para incorporar la topografía AR en el reverso de las lentes, con el fin de mejorar su eficiencia de concentración mediante la reducción de pérdidas por reflexión de la luz. En conclusión, esta tesis describe el desarrollo de superficies multifuncionales antirreflectantes basadas en nanoestructuras poliméricas inspiradas en el ojo de la polilla reforzadas con nanomateriales activos para conseguir mejores propiedades mecánicas, térmicas y resistencia a la intemperie, y que además presentan funcionalidades fotoinducidas de autolimpieza. Se demuestra la puesta a punto de la fabricación de las superficies AR y microlentes de Fresnel utilizando el formato de producción en masa NIL rollo a rollo, y por lo tanto se corrobora la validez de esta tecnología para la fabricación de superficies funcionales estructuradas dedicadas a aplicaciones reales. Programa de Doctorado en Ciencia e Ingeniería de Materiales por la Universidad Carlos III de Madrid Presidente: María Cruz García Gutiérrez.- Secretario: Juan Pedro Fernández Blázquez.- Vocal: Juan Ramón Cabanillas González

The thermal stability of antireflective moth-eye topographical features fabricated by nanoimprint lithography on poly (methyl methacrylate) (PMMA) incorporating TiO

Tesis doctoral inédita leída en la Universidad Carlos III de Madrid. Fecha de lectura: 24-9-2021.

Supplemental Document

11 pages, 5 figures, 1 table, supporting information https://doi.org//10.1371/journal.pone.0104536, The offshore displacement of commercial bottom trawling has raised concerns about the impact of this destructive fishing practice on the deep seafloor, which is in general characterized by lower resilience than shallow water regions. This study focuses on the flanks of La Fonera (or Palamós) submarine canyon in the Northwestern Mediterranean, where an intensive bottom trawl fishery has been active during several decades in the 400-800 m depth range. To explore the degree of alteration of surface sediments (0-50 cm depth) caused by this industrial activity, fishing grounds and control (untrawled) sites were sampled along the canyon flanks with an interface multicorer. Sediment cores were analyzed to obtain vertical profiles of sediment grain-size, dry bulk density, organic carbon content and concentration of the radionuclide 210Pb. At control sites, surface sediments presented sedimentological characteristics typical of slope depositional systems, including a topmost unit of unconsolidated and bioturbated material overlying sediments progressively compacted with depth, with consistently high 210Pb inventories and exponential decaying profiles of 210Pb concentrations. Sediment accumulation rates at these untrawled sites ranged from 0.3 to 1.0 cm y -1. Sediment properties at most trawled sites departed from control sites and the sampled cores were characterized by denser sediments with lower 210Pb surface concentrations and inventories that indicate widespread erosion of recent sediments caused by trawling gears. Other alterations of the physical sediment properties, including thorough mixing or grain-size sorting, as well as organic carbon impoverishment, were also visible at trawled sites. This work contributes to the growing realization of the capacity of bottom trawling to alter the physical properties of surface sediments and affect the seafloor integrity over large spatial scales of the deep-sea. © 2014 Martín et al., This work was funded by the HERMIONE project (http://www.eu-hermione.net) under the European Commission's Seventh Framework Programme (Grant agreement no: 226354) and by the Spanish national Research Plan (Ref. CTM2010-11084-E). J. Martín was funded through a JAEDOC contract within the Program «Junta para la Ampliación de Estudios», granted by Consejo Superior de Investigaciones Científicas (wwww.csic.es) and co-financed by the European Social Fund. P. Masqué received financial support through the ICREA (www.icrea.cat) Academia award

The thermal stability of antireflective moth-eye topographical features fabricated by nanoimprint lithography on poly (methyl methacrylate) (PMMA) incorporating TiO2nanoparticles is explored. The effect of nanoparticle load on the relaxation dynamics of the moth-eye nanostructure is evaluated via grazing incidence small angle x-ray scattering measurements byin situmonitoring the structural decay of the nanopatterns upon thermal annealing. It is demonstrated that the incorporation of TiO2nanoparticles to the imprinted surface nanocomposite films delays greatly the pattern relaxation which, in turn, enhances the stability of the patterned topography even at temperatures well above the polymer glass transition (Tg). The improved thermal behavior of the antireflective films will significantly enhance their functionality and performance in light-trapping applications where temperatures typically rise, such as solar devices or solar glass panels.