Spallative ablation of dielectrics by X-ray laser

Short laser pulse in wide range of wavelengths, from infrared to X-ray, disturbs electron-ion equilibrium and rises pressure in a heated layer. The case where pulse duration $\tau_L$ is shorter than acoustic relaxation time $t_s$ is considered in the paper. It is shown that this short pulse may cause thermomechanical phenomena such as spallative ablation regardless to wavelength. While the physics of electron-ion relaxation on wavelength and various electron spectra of substances: there are spectra with an energy gap in semiconductors and dielectrics opposed to gapless continuous spectra in metals. The paper describes entire sequence of thermomechanical processes from expansion, nucleation, foaming, and nanostructuring to spallation with particular attention to spallation by X-ray pulse

Nanocomposites of PLA containing ZnO nanofibers made by solvent cast 3D printing : production and characterization

PLA nanocomposites containing 1 wt% ZnO nanofibers have been prepared by solvent-cast 3D printing. The ZnO nanofibers were produced by electrospinning and dispersed in PLA by ultrasound. Scanning electron microscopy revealed that the fibers were dispersed throughout the nanocomposite. Surface specimen assessment by atomic force microscopy indicated the presence of nanofibers near the surface of the nanocomposite. TGA tests showed the nanocomposite had a lower thermal stability than the neat PLA, probably induced by PLA hydrolysis catalyzed by ZnO. DSC results revealed higher crystallinity in the nanocomposite, induced both by the presence of ZnO nanofibers and by the 3D printing process, though the 3D printing process showed to be more important in increasing the crystallinity. XRD results also showed a higher crystallinity for the nanocomposite. The study opens an interesting field for the development of PLA/ZnO nanocomposites using ZnO nanofibers made by electrospinning, e.g. in medical and packaging applications114271278COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIOR - CAPES00

Zno Micro And Nanofibers Made By Electrospinning: Fabrication And Characterization

In this study, the best conditions to obtain Zinc Oxide (ZnO) nanofibers were studied for further development of a composite with a biopolymer for application in scaffolds. Although the electrospinning of ZnO nanofiber is already known, there are still new aspects to be explored to optimize itsproduction. In this work were prepared six different solutions of poly(vinyl alcohol) - PVA with two different molecular weight, containing ZnO precursor, i.e. Zinc Acetate, using water or a mix of water and alcohol as solvents, and tested to understand how solution characteristics influence the final morphology of the ZnO nanofibres. This paper shows promising results for production ceramic nanofibers by electrospinning since parameters as viscosity, molecular weight, concentration, conductivity and surface tension are well controlled.820824Ramaseshan, R., Sundarrajan, S., Jose, R., Ramakrishna, S., Nanostructured ceramics by electrospinning (2007) J. Appl. Phys., 102, p. 102. , DecOhyama, M., Kouzuka, H., Yoko, T., Sol-gel preparation of ZnO films with extremely preferred orientation along (002) plane from zinc acetate solution (1997) Thin Solid Films, 306, pp. 78-85. , AugTakamura, N., Tagushi, K., Gunji, T., Abe, Y., Preparation of silicon oxycarbide ceramic films by pyrolysis of polyvinylsilsesquioxanes (1999) J. Sol-gel Scl. Technol., 16, p. 227. , NovLi, D., Xia, Y., Electrospinning of polymeric and ceramic nanofibers as uniaxially aligned arrays (2003) Nano Lett., 3, p. 555. , JulyGensheimer, M., Becker, M., Brandis-Heep, A., Wendorff, J.H., Thauer, R.K., Greiner, A., Novel biohybrid materials by electrospinning: Nanofibers of poly(ethylene oxide) and living bacteria (2007) Adv. Mater., 19, pp. 2480-2482. , SepKlingshirn, C., ZnO: From basics towards applications (2007) Chem. Phys. Chem., 8, pp. 782-803. , SepDing, B., Wang, M., Yu, J., Sun, G., Gas sensors based on electrospun nanofibers (2009) Sensors, 9, p. 1609. , MarchMoorer, W.R., Genet, J.M., Antibacterial activity of gutta-percha cones attributed to the zinc oxide component (1982) Oral Surg., Oral Med., Oral Pathol., 53, pp. 508-517. , MayWei, S., Zhou, M., Du, W., Improved acetone sensing properties of ZnO hollow nanofibers by single capillary electrospinning (2011) Sens. Actuators, B, 160, pp. 753-759. , DecLee, S., Multifunctionality of layered fabric systems based on electrospun polyurethane / zinc oxide nanocomposite fibers (2009) J. Appl. Polym. Sci., 114, pp. 3652-3658. , DecÖzgur, U., Alivov, Y., Liu, C., Teke, A., Reshchikov, M.A., Dogan, S., Avrutin, V., Morkoc, H., A comprehensive review of ZnO materials and devices (2005) J. Appl. Phys., 98, pp. 0413010-41301103. , AugOnozuka, K., Ding, B., Tsuge, Y., Naka, T., Yamazaki, M., Sugi, S., Ohno, S., Shiratori, S., Electrospinning processed nanofibrous TiO2 membranes for photovoltaic applications (2006) Nanotechnol., 17, p. 1026. , JanYaakob, Z., Khadem, D.J., Shahgaldi, S., Daud, W.R.W., Tasirin, S.M., The role of al and mg in the hydrogen storage of electrospun ZnO nanofibers (2002) Int. J. Hydrogen Energy, 37, pp. 8388-8394. , MayFujihara, S., Sasaki, C., Kimura, T., Effect of li and mg doping on microstructure and properties of sol-gel ZnO thin films (2001) Journal of European Ceramic Society, 21, pp. 2109-2112. , OutLi, D., Xia, Y., Electrospinning of nanofibers, reinventing the wheel? (2004) Adv. Mat., 16, pp. 1151-1170. , JulyKroski, A., Yim, K., Shivkumar, S., Effect of molecular weight on fibrous PVA produced by electrospinning (2004) Mat. Lett., 58, pp. 493-497. , JanNista, S.V.G., (2012) Desenvolvimento e Caracterização de Nanofibras de Acetato de Celulose para Liberação Controlada de Fármacos, , Masters dissertation, DEMBIO, Universidade Estadual de Campinas (UNICAMP), São PauloRamakrishna, S., Fujihara, K., Teo, W., Lim, T., Ma, Z., (2005) An Introduction to Electrospinning and Nanofibers, p. 349. , World Scientific Publishing Co. Pte. Ltd., SingaporeBetellheim, F.A., Brown, W.H., Campebell, M.K., Farrell, S.O., (2012) Introdução à Química Geral, , 9. ed. São Paulo: Cengage LearningGlordano, T.H., Drummond, S.E., The potentiometric determination of stability constants for zinc acetate complexes in aqueous solutions to 295°C (1991) Geochimica et Cosmochimica Acta, 55, pp. 2401-2415. , SepLeão, T.P., Martins, M.A., Santos, S.B., Carneiro, A.C.O., Determination of water content in ethanol by eletrical conductivity technique (2010) Global Science Technology, 3 (2), pp. 19-29. , AugJunior, W.J.P.S., Debacher, N.A., (2006) Determinação de Propriedades Superficiais Da Argila Montmorilonita Em Suspensão Aquosa de PVA Com Diferentes Graus de Hidrolise, , Universidade Federal de Santa Catarina, UFSC, Santa Catarina, SepAranha, I.B., Lucas, E.F., Poli (Álcool Vinílico) Modificado com Cadeias Hidrocarbônicas: Avaliação do Balanço Hidrófilo/Lipófilo (2001) Polímeros: Ciência e Tecnologia, 4, pp. 174-181. , NovShaw, D.J., (1975) Introduction to Colloid and Surface Chemistry, , E. BlücherFridrikh, S.V., Yu, J.H., Brenner, M.P., Rutledge, G.C., Controlling the fiber diameter during electrospinning (2003) Physical Review Letters, 40, pp. 1445021-1445024. , AprilJun, Z., Hou, H., Schaper, A., Wendorff, J.H., Greiner, A., Poly-L-lactide nanofibers by electrospinning - Influence of solution viscosity and electrical conductivity on fiber diameter and fiber morphology (2003) E-polymers, 9. , MarchUppatham, C.M., Nithitanakul, M., Supaphol, P., (2004) Ultrafine Electrospun Polyamide-6 Fibers: Effect of Solution Conditions on Morphology and Average Fiber Diameter, Macromolecular Chemistry and Physics, 205, pp. 2327-2338. , NovNishio, Y., Manley, R.S., Cellulose-poly(vinyl alcohol) blends prepared from solutions in N,N-dimethylacetamide-lithium chloride (1988) Macromol., 21, pp. 1270-1277. , MayYang, X., Shao, C., Guan, H., Li, X., Gong, J., Preparation and characterization of ZnO nanofibers by using electrospun PVA/zinc acetate composite fiber as precursor (2004) Inorg. 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Compatibilização de blendas de poliamida 6/ABS usando os copolímeros acrílicos reativos MMA-GMA e MMA-MA. Parte 2: Comportamento termomecânico e morfológico das blendas Compatibilization of Polyamide 6/ABS blends using MMA-GMA and MMA-MA reactive acrylic copolymers. Part 2. Thermal-mechanical and morphological behavior of blends

Blendas poliméricas de poliamida 6 (PA6) com acrilonitrila-butadieno-estireno (ABS) foram preparadas em extrusora de rosca dupla, utilizando-se os copolímeros metacrilato de metila - metacrilato de glicidila (MMA-GMA) e metacrilato de metila-anidrido maléico (MMA-MA) como agentes de compatibilização. O ABS, por si só, não foi capaz de tenacificar a PA6, apresentando uma morfologia de fases com grandes e pequenos aglomerados na matriz PA6. A introdução do copolímero MMA-GMA, como compatibilizante do sistema, não melhorou significativamente as propriedades de impacto da blenda PA6/ABS. As fotomicrografias obtidas por microscopia eletrônica de transmissão (MET) indicaram uma morfologia com duas populações distintas de ABS: aglomerados e pequenas partículas dispersas, resultando em uma distribuição não-uniforme de domínios de ABS. A blenda compatibilizada com MMA-MA foi supertenaz (> 800 J/m) na temperatura ambiente e em baixas temperaturas (~ -10 °C), com baixas concentrações de compatibilizante e baixos teores de MA no copolímero. As blendas PA6/ABS compatibilizadas com MMA-MA apresentaram uma morfologia de partículas bem dispersas e adequadamente distribuídas na matriz, evidenciando a presença efetiva do copolímero como agente de compatibilização reativo deste sistema.<br>Blends of Polyamide 6 (PA6) with acrylonitrile-butadiene-styrene (ABS) were prepared in a corotating twin-screw extruder, using the poly(methyl methacrylate-co-glycidyl methacrylate) (MMA-GMA) and poly(methyl methacrylate-co-maleic anhydride) (MMA-MA) copolymers as compatibilizing agents. The ABS by itself was not capable to toughen PA6 and showed a phase morphology with large and small agglomerates in the PA6 matrix. The introduction of MMA-GMA copolymer as a compatibilizing agent in the system did not significantly improve the impact properties of PA6/ABS blend. Transmission electron microscope (TEM) photomicrographs indicated a morphology with two distinct populations of ABS: agglomerates and small dispersed particles resulting in a non-uniform distribution of ABS domains. The compatibilized blend with MMA-MA was super-tough (> 800 J/m) at room temperature and low temperature (~ -10 °C) with small amounts of MA in the copolymer and small amounts of compatibilizer in the blend. The PA6/ABS compatibilized blends with MMA-MA showed a morphology of well dispersed and distributed rubber particles in PA6 matrix, thus demonstrating the effective presence of the copolymer as a compatibilizing reactive agent of this system