Key Production Parameters to Obtain Transparent Nanocellular PMMA

Transparent nanocellular polymethylmethacrylate (PMMA) with relative density around 0.4 is produced for the first time by using the gas dissolution foaming technique. The processing conditions and the typical characteristics of the cellular structure needed to manufacture this novel material are discovered. It is proved that low saturation temperatures (−32 °C) combined with high saturation pressures (6, 10, 20 MPa) allow increasing the solubility of PMMA up to values not reached before. In particular, the highest CO2 uptake ever reported for PMMA, (i.e., 48 wt%) is found for a saturation pressure of 20 MPa and a saturation temperature of −32 °C. Due to these processing conditions, cell nucleation densities of 1016 nuclei cm−3 and cell sizes clearly below 50 nm are achieved. The nanocellular polymers obtained, with cell sizes ten times smaller than the wavelength of visible light and very homogeneous cellular structures, show a significant transparency

Overcoming the Challenge of Producing Large and Flat Nanocellular Polymers: A Study with PMMA

Although nanocellular polymers are interesting materials with improved properties in comparison with conventional or microcellular polymers, the production of large and flat parts of those materials is still challenging. Herein, gas dissolution foaming process is used to produce large and flat nanocellular polymethylmethacrylate samples. In order to do that, the foaming step is performed in a hot press. The methodology is optimized to produce flat samples with dimensions of 100 × 100 × 6 mm3, relative densities in the range 0.25–0.55 and cell sizes around 250 nm. Additionally, foaming parameters are modified to study their influence on the final cellular structure, and the materials produced in this paper are compared with samples produced by using a most conventional approach in which foaming step is conducted in a thermal bath. Results obtained show that an increment in the foaming temperature leads to a reduction in relative density and an increase of cell nucleation density. Moreover, differences in the final cellular structure for materials produced by both foaming routes are studied, proving that although there exist some differences, the mechanisms governing the nucleation and growing are the same in both processes, leading to the production of homogeneous materials with very similar cellular structures

Encuentros con… charla con los youtubers Living Postureo.

Living Postureo son Victoria Martín de la Cova (Madrid, 1989) -licenciada en Periodismo y Máster en Guión de Cine y TV- y Nacho Pérez-Pardo (Santander, 1990), licenciado en Administración y Dirección de Empresas (ADE) y master en Producción Cinematográfica. Desde 2017 suben vídeos de contenido cómico a YouTube, y ya acumulan más de 60.000 suscriptores y millones de visualizaciones.Los temas abordados han girado en torno a los inicios de su trayectoria y formato escogido. Así como inspiraciones o influencias (mockumentaries, series, influencers reales…). Asimismo se han tocado temas como el humor como vehículo de ideas, humor y género, los límites del humor y proyectos futuros.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tec

Transparent nanocellular PMMA: Characterization and modeling of the optical properties

In this work, the optical properties of transparent nanocellular polymethylmethacrylate (PMMA) have been studied, experimental and theoretically. Transmittance measurements of samples presenting different cell sizes (14, 24, 39 and 225 nm) and a constant relative density of around 0.45 have been carried out obtaining values as high as 0.94 for the sample with the smaller cell size and a thickness of 0.05 mm. In addition, the light absorption coefficient has been measured as a function of cell size and wavelength. It has been found that the transmittance has a strong dependence with the wavelength, presenting these transparent materials Rayleigh scattering. On the other hand, the transmission of visible light through these nanocellular materials has been modelled for the first time. The developed model reproduces with good accuracy the trends observed in the experimental results and provides remarkable insights into the physics mechanisms controlling the optical behavior of these materials

El adverbio en el español de Argentina

Análisis descriptivo del uso del adverbio en el español de Argentina para mostrar la diversidad y uniformidad con respecto al español estándar del adverbio en un país americano del que aún queda mucho por investigar.El adverbio ha sido hasta hace poco tiempo una de las partes de la oración que menos atención ha recibido. Se elabora un extenso corpus y se estudia cada adverbio teniendo en cuenta los ejemplos recogidos. Se demuestra hay muy poca variación con el estándar y con lo que podría llamarse la norma culta panhispánica. El uso adverbial en el español de Argentina no difiere, a grandes rasgos, según este corpus, del estándar panhispánico y peninsular

Modeling the heat transfer by conduction of nanocellular polymers with bimodal cellular structures

Nanocellular polymers are a new generation of materials with the potential of being used as very efficient thermal insulators. It has been proved experimentally that these materials present the Knudsen effect, which strongly reduces the conductivity of the gas phase. There are theoretical equations to predict the thermal conductivity due to this Knudsen effect, but all the models consider an average cell size. In this work, we propose a model to predict the thermal conductivity due to the conduction mechanisms of nanocellular materials with bimodal cellular structures, that is, with two populations of cells, micro and nanocellular. The novelty of our work is to consider not only the average cell size, but the cell size distribution. The predictions of the model are compared with the experimental conductivity of two real bimodal systems based on poly(methyl methacrylate) (PMMA), and it is proved that this new model provides more accurate estimations of the conductivity than the models that do not consider the bimodality. Furthermore, this model could be applied to monomodal nanocellular polymers. In particular, for monomodal materials presenting a wide cell size distribution and at low densities, the model predicts important variations in comparison with the current models in the literature. This result indicates that the cell size distribution must be included in the estimations of the thermal conductivity of nanocellular polymer

Nanocellular Polymers with a Gradient Cellular Structure Based on Poly(methyl methacrylate)/Thermoplastic Polyurethane Blends Produced by Gas Dissolution Foaming

Graded structures and nanocellular polymers are two examples of advanced cellular morphologies. In this work, a methodology to obtain low-density graded nanocellular polymers based on poly(methyl methacrylate) (PMMA)/ thermoplastic polyurethane (TPU) blends produced by gas dissolution foaming is reported. A systematic study of the effect of the processing condition is presented. Results show that the melt-blending results in a solid nanostructured material formed by nanometric TPU domains. The PMMA/ TPU foamed samples show a gradient cellular structure, with a homogeneous nanocellular core. In the core, the TPU domains act as nucleating sites, enhancing nucleation compared to pure PMMA and allowing the change from a microcellular to a nanocellular structure. Nonetheless, the outer region shows a gradient of cell sizes from nano- to micron-sized cells. This gradient structure is attributed to a non-constant pressure profile in the samples due to gas desorption before foaming. The nucleation in the PMMA/ TPU increases as the saturation pressure increases. Regarding the effect of the foaming conditions, it is proved that it is necessary to have a fine control to avoid degeneration of the cellular materials. Graded nanocellular polymers with relative densities of 0.16–0.30 and cell sizes ranging 310–480 nm (in the nanocellular core) are obtained

Low-density PMMA/MAM nanocellular polymers using low MAM contents: Production and characterization

Low-density nanocellular polymers are required to take advantage of the full potential of these materials as high efficient thermal insulators. However, their production is still a challenging task. One promising approach is the use of nanostructured polymer blends of poly(methyl methacrylate) (PMMA) and a block copolymer poly(methyl methacrylate)-poly(butyl acrylate)-poly(methyl methacrylate) (MAM), which are useful for promoting nucleation but seem to present a severe drawback, as apparently avoid low relative densities. In this work, new strategies to overcome this limitation and produce low-density nanocellular materials based on these blends are investigated. First, the effect of very low amounts of the MAM copolymer is analysed. It is detected that nanostructuration can be prevented using low copolymer contents, but nucleation is still enhanced as a result of the copolymer molecules with high CO2 affinity dispersed in the matrix, so nanocellular polymers are obtained using very low percentages of the copolymer. Second, the influence of the foaming temperature is studied. Results show that for systems in which there is not a clear nanostructuration, cells can grow more freely and smaller relative densities can be achieved. For these studies, blends of PMMA with MAM with copolymer contents from 10 wt% and as low as 0.1 wt% are used. For the first time, the production strategies proposed in this work have allowed obtaining low density (relative density 0.23) nanocellular polymers based on PMMA/MAM blends. Graphical abstrac

Recognising oneself as educator. Findings from a case study conducted in the internship training for Social Education Bachelor's Degree.

In this paper I share the results of the analysis of a case study of a Social Education student through a qualitative enquiry with a narrative approach (Clandinin and Connelly, 1994, 2000; Van Manen, 2003, 1990). It delves into her experience and formative trajectory within the Practicum course of the Bachelor's Degree in Social Education at the University of Malaga (Spain); a course that took place during three consecutive years, oriented to the realisation of training practices in profesional contexts. The focus of this study, which is part of a larger thesis project, is to approach the development of professional knowledge in the initial training of social educators in the context of this subject. Being a social educator requires more than just knowing what to do and how to do it. Social education professionals develop their profession in situations and problems that cannot be solved by applying knowledge, but by developing practical knowledge that allows them to make situational judgements about what is appropriate and desirable (Biesta, 2013, 2017) at each moment and with each person. Initial training plays an important role in the development of professional identity and critical thinking that allows students to construct their own knowledge, which is indispensable for the educational profession exercise: determining who they want to be and how they want to do their profession. That is, learning to act on the basis of who they are, becoming aware of their own pedagogical being and taking responsibility for their actions (Blanco and Sierra, 2013). In this sense, this context of theoretical-practical and professional training is one of the most important and highly valued subjects within the Degree in Social Education, mainly due to its proximity to professional practice. During these practical periods, students attend socioeducational centres attached to the university, for several days a week, and are accompanied by an academic tutor.Universidad de Málaga. Campus de Excelencia Internacional Andalucía Tech

Production and characterization of nanocellular polyphenylsulfone foams

Producción CientíficaNanocellular foamshavebeenproducedbymeansofagasdissolutionprocessusingpolyphenylsulfone (PPSU) asmatrixpolymer.Cellsizesintherange20–30 nmandcellnucleationdensitieshigherthan 1015 cm 3 havebeenachievedformaterialswithrelativedensitiesintherange0.65–0.75. Theinfluence of bothsaturationpressureandfoamingtemperaturehasbeenstudied.Ontheonehand,ithasbeen provedthatthereisalargeinfluence oftheamountofgas(CO2) absorbedinthe final cellularstructure, in factithasbeenfoundacriticalCO2 uptake between9%and9.5%atwhichthecellsizesevolvefromthe micro tothenanoscale.Ontheotherhand,ithasbeenfoundthatthereisawiderangeoffoaming parameters(foamingtimeandfoamingtemperature)inwhichnanocellularfoamscanbeproduced.Financial supportfromFPUgrantFPU14/02050(V.Bernardo) from theSpanishMinistryofEducationandJuntaofCastileand Leon grantQ4718001C(J.Martín-deLeón)isgratefullyacknowl- edged.FinancialassistancefromMINECO(MAT2012-34901and MAT2015-69234-R)andtheJuntaofCastileandLeon(VA035U13) is gratefullyacknowledged