Thermal and Dielectric Characterization of Multi-Walled Carbon NanotubesThermoplastic Polyurethanes Composites

[EN] Multi-walled carbon nanotubes-thermoplastic polyurethanes composites were characterized by means of differential scanning calorimetry and dielectric relaxation spectroscopy. The composite is characterized by two glass transition temperatures T (g) . The T (g) associated with the soft segment decreases by increasing of carbon nanotubes content, while carbon nanotubes content has practically no effect on the value of the T-g associated with the hard segments. It was observed that rising the temperature and carbon nanotubes content resulted in the increased of both the dielectric permittivity and the loss factor. The presence of carbon nanotubes produces an enhancement of charge carriers trapping, increasing the electrical conductivity. The electrical conductivity of the composite was found to exhibit an insulator to conductor transition at a carbon nanotubes critical content, i.e., the percolation threshold, near 6 wt %.MJS and MC acknowledge the financial support of the DGCYT through Grant MAT2015-63955-R.Sanchis Sánchez, MJ.; Carsí Rosique, M.; Gracia-Fernandez, C. (2017). Thermal and Dielectric Characterization of Multi-Walled Carbon NanotubesThermoplastic Polyurethanes Composites. Polymer Science Series A. 59(4):543-553. https://doi.org/10.1134/S0965545X17040083S543553594D. W. Schaefer and R. S. Justice, Macromolecules 40 (24), 8501 (2007).D. R. Raul and L. M. Robeson, Polymer 49 (15), 3187 (2008).P. J. Brigandi, J. M. Cogen, and R. A. Pearson, Polym. Eng. Sci. 54 (1), 1 (2014).H. Deng, L. Lin, M. Ji, S. Zhang, M. Yang, and Q. Fu, Prog. Polym. Sci. 39 (4), 627 (2014).Polymer-Matrix Composites. Types, Applications and Performance, Ed. by R. Kumar (Nova Sci. Publ., New York, 2014).Z. Wenying and Y. Demei, J. Appl. Polym. Sci. 118 (6), 3156 (2010).Y. P. Mamunya, V. V. Davydenko, P. Pissis, and E. V. Lebedev, Eur. Polym. J. 38 (9), 1887 (2002)B. Redondo-Foj, P. Ortiz-Serna, M. Carsí, M. J. Sanchis, M. Culebras, C. M. Gomez, and A. Cantarero, Polym. Int. 64, 284 (2015).S. Deng, Y. Zhu, X. Qi, W. Yu, F. Chen, and Q. Fu, RSC Adv. 6 (51), 45578 (2016).M. Khissi, M. El Hasnaoui, J. Belattar, M. P. F. Graca, M. E. Achour, and L. C. Costa, J. Mater. Environ. Sci. 2 (3), 281 (2011).M. Hindermann-Bischoff and F. Ehrburger-Dolle, Carbon 39 (3), 375 (2001).I. Balberg, Carbon 40 (2), 139 (2002).M. Moniruzzaman and K. I. Winey, Macromolecules 39, 5194 (2006).A. Bharati, R. Cardinaels, J. W. Seo, M. Wubbenhorst, and P. Moldenaers, Polymer 79 (19), 271 (2015)Szycher's Handbook of Polyurethanes, Ed. by M. Szycher (CRC Press, Washington, DC, 1999).C. Prisacariu, Polyurethane Elastomers. From Morphology to Mechanical Aspects (Springer, New York, 2011).P. Król, Prog. Mater. Sci. 52 (6), 915 (2007).P. R. de C. Coelho Filho, M. S. Marchesin, A. R. Morales, and J. R. Bartoli, Mater. Res. 17 (1), 127 (2014).R. H. Baughman, A. A. Zakhidov, and W. A. de Heer, Science 297 (5582), 787 (2002).J. Kim and Y. Son, Polymer 88, 29 (2016)M. A. Nikje Mir and A. Yaghoubi, Polimery 59(11–12), 776 (2014).C. Kingston, R. Zepp, A. Andrady, D. Boverho, R. Fehir, D. Hawkins, J. Roberts, P. Sayre, B. Shelton, Y. Sultan, V. Vejins, and W. Wohlleben, Carbon 68, 33 (2014).Anelastic and Dielectric Effects in Polymeric Solids, Ed. by N. G. McCrum, B. E. Read, and G. Williams (Wiley, London, 1967).In Broadband Dielectric Spectroscopy, Ed. by F. Kremer, and A. Schonhals (Springer, Berlin, 2003).E. Riande and R. Diaz-Calleja, Electrical Properties of Polymers (Marcel Dekker, New York, 2004).I. M. Hodge, K. L. Ngai, and C. T. Moynihan, J. Non-Cryst. Solids 351 (2), 104 (2005).A. Eceiza, M.D. Martin, K. de la Caba, G. Kortaberria, N. Gabilondo, M. A. Corcuera, and I. Mondragon, Polym. Eng. Sci. 48 (2), 297 (2008)A. K. Jonscher, Universal Relaxation Law: A Sequel to Dielectric Relaxation in Solids (Chelsea Dielectrics Press, London, 1996), Chap. 5.A. K. Jonscher, Nature 267, 673 (1977).G. Li, L. Feng, P. Tong, and Z. Zhai, Prog. Org. Coat. 90, 284 (2016)K. Petrie, M. Kontopoulou, and A. Docoslis, Polym. Compos. 37 (9), 2794 (2016)N. Aranburu and J. I. Eguiazabal, Polym. Compos. 35 (3), 587 (2014)Impedance Spectroscopy. Theory, Experiment, and Applications, Ed. by E. Barsoukov and J. R. Macdonals (Wiley Intersci., New York, 2005).S. Havriliak and S. J. Havriliak, Dielectric and Mechanical Relaxation in Materials (Hanser, Munich, 1997), p. 57.S. Havriliak and S. Negami, Polymer 8 (4), 161 (1967)

Evaluation of Natural Rubber Specific Heat Capacity at High Pressures from DSC Experimental Data at Atmospheric Pressure

[EN] The natural rubber specific heat capacity dependence on pressure was estimated on thermodynamic grounds on the basis of the values empirically determined from differential scanning calorimetry data, (in the temperature range of 70 to 50 C), and by means of the Tait equation of state (in the pressure range of 0.1 240 MPa). It was found that the specific heat capacity decreases with pressure, being the dependency more pronounced at low pressures.This work was financially supported by the DGCYT through Grant MAT2008-06725-C03 and by Generalitat Valenciana through Grant No. ACOMP/2010/204.Ortiz Serna, MP.; Díaz Calleja, R.; Sanchis Sánchez, MJ. (2012). Evaluation of Natural Rubber Specific Heat Capacity at High Pressures from DSC Experimental Data at Atmospheric Pressure. Journal of Applied Polymer Science. 128(4):2269-2272. doi:10.1002/app.38118S22692272128

Relaxation behavior of semiflexible polymers at very low frequencies

[EN] The dielectric activity of poly(monocyclohexylmethylene itaconate) (PMCI) and poly(dicyclohexylmethylene itaconate) (PDCI) in the glassy region and in the glass-rubber transition is studied by thermostimulated discharge current (TSDC) techniques. The spectra obtained by global TSDC experiments show a prominent alpha-glass-rubber relaxation peak with maxima located at 97 and 55 degrees C for PMCI and PDCI, respectively, following in decreasing order of temperature for a well developed beta absorption and a comparatively low intensity relaxation. Better resolution of the relaxation behavior of these polymers in the glassy region is obtained by calculating the components of the complex dielectric permittivity epsilon* at extremely low frequencies from partial TSDC experiments. The ac spectra thus obtained suggest that the beta absorption is composed by two relaxations, each of them presumably associated with the motions of a side group. The differences observed in these spectra with those reported for the beta mechanical relaxation reported for these polymers in the literature are interpreted in terms of the restrictions that the side groups produce in the conformational space of phase of the backbone. These restrictions also explain the small changes in enthalpy in the glass-rubber transition which preclude the possibility of obtaining the glass-rubber transition temperature of these polymers by differential scanning calorimetric techniques. (C) 1997 American Institute of Physics.Díaz Calleja, R.; Sanchis Sánchez, MJ.; Alvarez, C.; Riande, E. (1997). Relaxation behavior of semiflexible polymers at very low frequencies. Journal of Applied Physics. 81(8):3685-3691. doi:10.1063/1.364743S3685369181

Thermal effects on the structure and relaxation properties of poly(monocyclopentyl itaconate)

[EN] The effect of thermal treatment and subsequent chemical structural modifications on the viscoelastic and dielectric properties of PMCPI (poly(monocyclopentyl itaconate)) was studied. The low temperature relaxation (gamma-relaxation) is unaffected by the thermal history or chemical modifications. The intermediate relaxation (beta-relaxation) is shifted by about 40 degrees C to higher temperature after thermal treatment. The alpha-relaxation (related to the glass transition temperature T-g) suffers more striking changes when moving to higher temperatures.Díaz Calleja, R.; Sanchis Sánchez, MJ.; Gargallo, L.; Radic, D. (1995). Thermal effects on the structure and relaxation properties of poly(monocyclopentyl itaconate). Macromolecular Chemistry and Physics. 196(11):3789-3796. doi:10.1002/macp.1995.021961129S378937961961

Memory function on dielectric relaxation

[EN] The second-order memory function ~SOMF! for the dicyclohexylmetyl-2metyl succinate is obtained by using simple numerical manipulation of the experimental dielectric data. According to the prescription given in a previous paper @J. Chem. Phys. 109, 9057 ~1998!#, the frequency behavior of the real and imaginary parts of the SOMF is discussed in terms of the Havriliak-Negami equation of the dielectric function, and together with the three-variable model describing the evolution of the torque-autocorrelation function. Furthermore, in this paper we present the temperature dependence of the parameters, which characterize the SOMF behavior for two ester substances. © 2000 American Institute of Physics. @S0021-9606~00!51048-4#This work was supported in part by the UPV. One of the authors L. F del C. wishes to thank DGAPA-UNAM for support from Grant No. IN119200. Authors of the UPV also thank the Science and Technology Office of Spain for Grant No. MAT 1999-1127-C04-03.Díaz-Calleja, R.; García Bernabé, A.; Sanchis Sánchez, MJ.; Del Castillo, L. (2000). Memory function on dielectric relaxation. The Journal of Chemical Physics. 113(24):11258-11263. https://doi.org/10.1063/1.1326913S11258112631132

Effect of Chitin Whiskers on the Molecular Dynamics of Carrageenan-Based Nanocomposites

[EN] Films of carrageenan (KC) and glycerol (g) with different contents of chitin nanowhiskers (CHW) were prepared by a solution casting process. The molecular dynamics of pure carrageenan (KC), carrageenan/glycerol (KCg) and KCg with different quantities of CHWs as a filler was studied using dielectric relaxation spectroscopy. The analysis of the CHW effect on the molecular mobility at the glass transition, T-g, indicates that non-attractive intermolecular interactions between KCg and CHW occur. The fragility index increased upon CHW incorporation, due to a reduction in the polymer chains mobility produced by the CHW confinement of the KCg network. The apparent activation energy associated with the relaxation dynamics of the chains at T-g slightly increased with the CHW content. The filler nature effect, CHW or montmorillonite (MMT), on the dynamic mobility of the composites was analyzed by comparing the dynamic behavior of both carrageenan-based composites (KCg/xCHW, KCg/xMMT).This research was funded by the DGCYT grant number [MAT2015-63955-R] and the Vice-Rectorate for Research of the Pontificia Universidad Catolica del Peru and the the Peruvian Science and Technology Program (INNOVATE-PERU) And The APC was funded by MDPI.Carsí Rosique, M.; Sanchis Sánchez, MJ.; Gómez, CM.; Rodriguez, S.; García-Torres, F. (2019). Effect of Chitin Whiskers on the Molecular Dynamics of Carrageenan-Based Nanocomposites. Polymers. 11(6):1-16. https://doi.org/10.3390/polym11061083116116Zheng, Y., Monty, J., & Linhardt, R. J. (2015). Polysaccharide-based nanocomposites and their applications. Carbohydrate Research, 405, 23-32. doi:10.1016/j.carres.2014.07.016Jamróz, E., Kulawik, P., & Kopel, P. (2019). The Effect of Nanofillers on the Functional Properties of Biopolymer-Based Films: A Review. Polymers, 11(4), 675. doi:10.3390/polym11040675Park, S.-B., Lih, E., Park, K.-S., Joung, Y. K., & Han, D. K. (2017). Biopolymer-based functional composites for medical applications. Progress in Polymer Science, 68, 77-105. doi:10.1016/j.progpolymsci.2016.12.003Xie, F., Pollet, E., Halley, P. J., & Avérous, L. (2013). Starch-based nano-biocomposites. Progress in Polymer Science, 38(10-11), 1590-1628. doi:10.1016/j.progpolymsci.2013.05.002Zhang, R., Wang, X., Wang, J., & Cheng, M. (2018). Synthesis and Characterization of Konjac Glucomannan/Carrageenan/Nano-silica Films for the Preservation of Postharvest White Mushrooms. Polymers, 11(1), 6. doi:10.3390/polym11010006Rhim, J.-W., Park, H.-M., & Ha, C.-S. (2013). Bio-nanocomposites for food packaging applications. Progress in Polymer Science, 38(10-11), 1629-1652. doi:10.1016/j.progpolymsci.2013.05.008Müller, K., Bugnicourt, E., Latorre, M., Jorda, M., Echegoyen Sanz, Y., Lagaron, J., … Schmid, M. (2017). Review on the Processing and Properties of Polymer Nanocomposites and Nanocoatings and Their Applications in the Packaging, Automotive and Solar Energy Fields. Nanomaterials, 7(4), 74. doi:10.3390/nano7040074Shankar, S., Reddy, J. P., Rhim, J.-W., & Kim, H.-Y. (2015). Preparation, characterization, and antimicrobial activity of chitin nanofibrils reinforced carrageenan nanocomposite films. Carbohydrate Polymers, 117, 468-475. doi:10.1016/j.carbpol.2014.10.010Corvaglia, S., Rodriguez, S., Bardi, G., Torres, F. G., & Lopez, D. (2016). Chitin whiskers reinforced carrageenan films as low adhesion cell substrates. International Journal of Polymeric Materials and Polymeric Biomaterials, 65(11), 574-580. doi:10.1080/00914037.2016.1149846Shojaee-Aliabadi, S., Mohammadifar, M. A., Hosseini, H., Mohammadi, A., Ghasemlou, M., Hosseini, S. M., … Khaksar, R. (2014). Characterization of nanobiocomposite kappa-carrageenan film with Zataria multiflora essential oil and nanoclay. International Journal of Biological Macromolecules, 69, 282-289. doi:10.1016/j.ijbiomac.2014.05.015Reddy, M. M., Vivekanandhan, S., Misra, M., Bhatia, S. K., & Mohanty, A. K. (2013). Biobased plastics and bionanocomposites: Current status and future opportunities. Progress in Polymer Science, 38(10-11), 1653-1689. doi:10.1016/j.progpolymsci.2013.05.006Wang, P., Zhao, X., Lv, Y., Li, M., Liu, X., Li, G., & Yu, G. (2012). Structural and compositional characteristics of hybrid carrageenans from red algae Chondracanthus chamissoi. Carbohydrate Polymers, 89(3), 914-919. doi:10.1016/j.carbpol.2012.04.034Byankina (Barabanova), A. O., Sokolova, E. V., Anastyuk, S. D., Isakov, V. V., Glazunov, V. P., Volod’ko, A. V., … Yermak, I. M. (2013). Polysaccharide structure of tetrasporic red seaweed Tichocarpus crinitus. Carbohydrate Polymers, 98(1), 26-35. doi:10.1016/j.carbpol.2013.04.063Stortz, C. A., & Cerezo, A. S. (1992). The 13C NMR spectroscopy of carrageenans: calculation of chemical shifts and computer-aided structural determination. Carbohydrate Polymers, 18(4), 237-242. doi:10.1016/0144-8617(92)90088-8Rodriguez, S. A., Weese, E., Nakamatsu, J., & Torres, F. (2016). Development of Biopolymer Nanocomposites Based on Polysaccharides Obtained from Red AlgaeChondracanthus chamissoiReinforced with Chitin Whiskers and Montmorillonite. Polymer-Plastics Technology and Engineering, 55(15), 1557-1564. doi:10.1080/03602559.2016.1163583Mitsuiki, M., Yamamoto, Y., Mizuno, A., & Motoki, M. (1998). Glass Transition Properties as a Function of Water Content for Various Low-Moisture Galactans. Journal of Agricultural and Food Chemistry, 46(9), 3528-3534. doi:10.1021/jf9709820Picker, K. M. (1999). The use of carrageenan in mixture with microcrystalline cellulose and its functionality for making tablets. European Journal of Pharmaceutics and Biopharmaceutics, 48(1), 27-36. doi:10.1016/s0939-6411(99)00009-0Kasapis, S., & Mitchell, J. R. (2001). Definition of the rheological glass transition temperature in association with the concept of iso-free-volume. International Journal of Biological Macromolecules, 29(4-5), 315-321. doi:10.1016/s0141-8130(01)00180-5Fouda, M. M. G., El-Aassar, M. R., El Fawal, G. F., Hafez, E. E., Masry, S. H. D., & Abdel-Megeed, A. (2015). k-Carrageenan/poly vinyl pyrollidone/polyethylene glycol/silver nanoparticles film for biomedical application. International Journal of Biological Macromolecules, 74, 179-184. doi:10.1016/j.ijbiomac.2014.11.040Arof, A. K., Shuhaimi, N. E. A., Alias, N. A., Kufian, M. Z., & Majid, S. R. (2010). Application of chitosan/iota-carrageenan polymer electrolytes in electrical double layer capacitor (EDLC). Journal of Solid State Electrochemistry, 14(12), 2145-2152. doi:10.1007/s10008-010-1050-8Rescignano, N., Fortunati, E., Armentano, I., Hernandez, R., Mijangos, C., Pasquino, R., & Kenny, J. M. (2015). Use of alginate, chitosan and cellulose nanocrystals as emulsion stabilizers in the synthesis of biodegradable polymeric nanoparticles. Journal of Colloid and Interface Science, 445, 31-39. doi:10.1016/j.jcis.2014.12.032Chang, P. R., Jian, R., Yu, J., & Ma, X. (2010). Starch-based composites reinforced with novel chitin nanoparticles. Carbohydrate Polymers, 80(2), 420-425. doi:10.1016/j.carbpol.2009.11.041Zeng, J.-B., He, Y.-S., Li, S.-L., & Wang, Y.-Z. (2011). Chitin Whiskers: An Overview. Biomacromolecules, 13(1), 1-11. doi:10.1021/bm201564aVillanueva, M. E., Salinas, A., Díaz, L. E., & Copello, G. J. (2015). Chitin nanowhiskers as alternative antimicrobial controlled release carriers. New Journal of Chemistry, 39(1), 614-620. doi:10.1039/c4nj01522cKameda, T., Miyazawa, M., Ono, H., & Yoshida, M. (2005). Hydrogen Bonding Structure and Stability of?-Chitin Studied by13C Solid-State NMR. Macromolecular Bioscience, 5(2), 103-106. doi:10.1002/mabi.200400142MARCHESSAULT, R. H., MOREHEAD, F. F., & WALTER, N. M. (1959). Liquid Crystal Systems from Fibrillar Polysaccharides. Nature, 184(4686), 632-633. doi:10.1038/184632a0Paillet, M., & Dufresne, A. (2001). Chitin Whisker Reinforced Thermoplastic Nanocomposites. Macromolecules, 34(19), 6527-6530. doi:10.1021/ma002049vGopalan Nair, K., & Dufresne, A. (2003). Crab Shell Chitin Whisker Reinforced Natural Rubber Nanocomposites. 1. Processing and Swelling Behavior. Biomacromolecules, 4(3), 657-665. doi:10.1021/bm020127bHuang, Y., Yao, M., Zheng, X., Liang, X., Su, X., Zhang, Y., … Zhang, L. (2015). Effects of Chitin Whiskers on Physical Properties and Osteoblast Culture of Alginate Based Nanocomposite Hydrogels. Biomacromolecules, 16(11), 3499-3507. doi:10.1021/acs.biomac.5b00928Morin, A., & Dufresne, A. (2002). Nanocomposites of Chitin Whiskers from Riftia Tubes and Poly(caprolactone). Macromolecules, 35(6), 2190-2199. doi:10.1021/ma011493aWatthanaphanit, A., Supaphol, P., Tamura, H., Tokura, S., & Rujiravanit, R. (2008). Fabrication, structure, and properties of chitin whisker-reinforced alginate nanocomposite fibers. Journal of Applied Polymer Science, 110(2), 890-899. doi:10.1002/app.28634Salaberria, A. M., Diaz, R. H., Labidi, J., & Fernandes, S. C. M. (2015). Preparing valuable renewable nanocomposite films based exclusively on oceanic biomass – Chitin nanofillers and chitosan. Reactive and Functional Polymers, 89, 31-39. doi:10.1016/j.reactfunctpolym.2015.03.003Rodríguez, S., Gatto, F., Pesce, L., Canale, C., Pompa, P. P., Bardi, G., … Torres, F. G. (2017). Monitoring cell substrate interactions in exopolysaccharide-based films reinforced with chitin whiskers and starch nanoparticles used as cell substrates. International Journal of Polymeric Materials and Polymeric Biomaterials, 67(6), 333-339. doi:10.1080/00914037.2017.1297942Pazmiño Betancourt, B. A., Douglas, J. F., & Starr, F. W. (2013). Fragility and cooperative motion in a glass-forming polymer–nanoparticle composite. Soft Matter, 9(1), 241-254. doi:10.1039/c2sm26800kSanchis, M. J., Carsí, M., Culebras, M., Gómez, C. M., Rodriguez, S., & Torres, F. G. (2017). Molecular dynamics of carrageenan composites reinforced with Cloisite Na+ montmorillonite nanoclay. Carbohydrate Polymers, 176, 117-126. doi:10.1016/j.carbpol.2017.08.012Wu, J., Zhang, K., Girouard, N., & Meredith, J. C. (2014). Facile Route to Produce Chitin Nanofibers as Precursors for Flexible and Transparent Gas Barrier Materials. Biomacromolecules, 15(12), 4614-4620. doi:10.1021/bm501416qSauti, G., & McLachlan, D. S. (2007). Impedance and modulus spectra of the percolation system silicon–polyester resin and their analysis using the two exponent phenomenological percolation equation. Journal of Materials Science, 42(16), 6477-6488. doi:10.1007/s10853-007-1564-3Johari, G. P., Kim, S., & Shanker, R. M. (2007). Dielectric Relaxation and Crystallization of Ultraviscous Melt and Glassy States of Aspirin, Ibuprofen, Progesterone, and Quinidine. Journal of Pharmaceutical Sciences, 96(5), 1159-1175. doi:10.1002/jps.20921Anastasiadis, S. H., Karatasos, K., Vlachos, G., Manias, E., & Giannelis, E. P. (2000). Nanoscopic-Confinement Effects on Local Dynamics. Physical Review Letters, 84(5), 915-918. doi:10.1103/physrevlett.84.915Böhning, M., Goering, H., Fritz, A., Brzezinka, K.-W., Turky, G., Schönhals, A., & Schartel, B. (2005). Dielectric Study of Molecular Mobility in Poly(propylene-graft-maleic anhydride)/Clay Nanocomposites. Macromolecules, 38(7), 2764-2774. doi:10.1021/ma048315cHodge, I. M., Ngai, K. L., & Moynihan, C. T. (2005). Comments on the electric modulus function. Journal of Non-Crystalline Solids, 351(2), 104-115. doi:10.1016/j.jnoncrysol.2004.07.089Havriliak, S., & Negami, S. (2007). A complex plane analysis of α-dispersions in some polymer systems. Journal of Polymer Science Part C: Polymer Symposia, 14(1), 99-117. doi:10.1002/polc.5070140111TSANGARIS, G. M., PSARRAS, G. C., & TSANGARIS, G. M. (1998). Electric modulus and interfacial polarization in composite polymeric systems. Journal of Materials Science, 33(8), 2027-2037. doi:10.1023/a:1004398514901Fulcher, G. S. (1925). ANALYSIS OF RECENT MEASUREMENTS OF THE VISCOSITY OF GLASSES. Journal of the American Ceramic Society, 8(6), 339-355. doi:10.1111/j.1151-2916.1925.tb16731.xTammann, G., & Hesse, W. (1926). Die Abhängigkeit der Viscosität von der Temperatur bie unterkühlten Flüssigkeiten. Zeitschrift für anorganische und allgemeine Chemie, 156(1), 245-257. doi:10.1002/zaac.19261560121Fragiadakis, D., Pissis, P., & Bokobza, L. (2005). Glass transition and molecular dynamics in poly(dimethylsiloxane)/silica nanocomposites. Polymer, 46(16), 6001-6008. doi:10.1016/j.polymer.2005.05.080Rittigstein, P., & Torkelson, J. M. (2006). Polymer-nanoparticle interfacial interactions in polymer nanocomposites: Confinement effects on glass transition temperature and suppression of physical aging. Journal of Polymer Science Part B: Polymer Physics, 44(20), 2935-2943. doi:10.1002/polb.20925Oh, H., & Green, P. F. (2009). Polymer chain dynamics and glass transition in athermal polymer/nanoparticle mixtures. Nature Materials, 8(2), 139-143. doi:10.1038/nmat2354Riggleman, R. A., Yoshimoto, K., Douglas, J. F., & de Pablo, J. J. (2006). Influence of Confinement on the Fragility of Antiplasticized and Pure Polymer Films. Physical Review Letters, 97(4). doi:10.1103/physrevlett.97.045502Doolittle, A. K. (1951). Studies in Newtonian Flow. II. The Dependence of the Viscosity of Liquids on Free‐Space. Journal of Applied Physics, 22(12), 1471-1475. doi:10.1063/1.1699894Doolittle, A. K. (1952). Studies in Newtonian Flow. III. The Dependence of the Viscosity of Liquids on Molecular Weight and Free Space (in Homologous Series). Journal of Applied Physics, 23(2), 236-239. doi:10.1063/1.1702182Plazek, D. J., & Ngai, K. L. (1991). Correlation of polymer segmental chain dynamics with temperature-dependent time-scale shifts. Macromolecules, 24(5), 1222-1224. doi:10.1021/ma00005a044Merino, E. G., Atlas, S., Raihane, M., Belfkira, A., Lahcini, M., Hult, A., … Correia, N. T. (2011). Molecular dynamics of poly(ATRIF) homopolymer and poly(AN-co-ATRIF) copolymer investigated by dielectric relaxation spectroscopy. European Polymer Journal, 47(7), 1429-1446. doi:10.1016/j.eurpolymj.2011.04.006Böhmer, R., Ngai, K. L., Angell, C. A., & Plazek, D. J. (1993). Nonexponential relaxations in strong and fragile glass formers. The Journal of Chemical Physics, 99(5), 4201-4209. doi:10.1063/1.466117Roland, C. M., & Ngai, K. L. (1991). Segmental relaxation and molecular structure in polybutadienes and polyisoprene. Macromolecules, 24(19), 5315-5319. doi:10.1021/ma00019a016Roland, C. M., & Ngai, K. L. (1992). Segmental relaxation and molecular structure in polybutadienes and polyisoprene. [Erratum to document cited in CA115(14):137101w]. Macromolecules, 25(6), 1844-1844. doi:10.1021/ma00032a038Ngai, K. L., & Roland, C. M. (1993). Chemical structure and intermolecular cooperativity: dielectric relaxation results. Macromolecules, 26(25), 6824-6830. doi:10.1021/ma00077a019Roland, C. M. (1992). Terminal and segmental relaxations in epoxidized polyisoprene. Macromolecules, 25(25), 7031-7036. doi:10.1021/ma00051a047Angell, C. A., Poole, P. H., & Shao, J. (1994). Glass-forming liquids, anomalous liquids, and polyamorphism in liquids and biopolymers. Il Nuovo Cimento D, 16(8), 993-1025. doi:10.1007/bf02458784Roland, C. M., & Ngai, K. L. (1996). The anomalous Debye–Waller factor and the fragility of glasses. The Journal of Chemical Physics, 104(8), 2967-2970. doi:10.1063/1.471117Hodge, I. M. (1987). Effects of annealing and prior history on enthalpy relaxation in glassy polymers. 6. Adam-Gibbs formulation of nonlinearity. Macromolecules, 20(11), 2897-2908. doi:10.1021/ma00177a044Hodge, I. M. (1996). Strong and fragile liquids — a brief critique. Journal of Non-Crystalline Solids, 202(1-2), 164-172. doi:10.1016/0022-3093(96)00151-2Roland, C. M., & Ngai, K. L. (1997). Commentary on ‘Strong and fragile liquids - A brief critique’. Journal of Non-Crystalline Solids, 212(1), 74-76. doi:10.1016/s0022-3093(96)00684-9Angell, C. A. (1997). Why C1 = 16–17 in the WLF equation is physical—and the fragility of polymers. Polymer, 38(26), 6261-6266. doi:10.1016/s0032-3861(97)00201-2Angell, C. A. (1995). Formation of Glasses from Liquids and Biopolymers. Science, 267(5206), 1924-1935. doi:10.1126/science.267.5206.1924Angell, C. . (1991). Relaxation in liquids, polymers and plastic crystals — strong/fragile patterns and problems. Journal of Non-Crystalline Solids, 131-133, 13-31. doi:10.1016/0022-3093(91)90266-9Kunal, K., Robertson, C. G., Pawlus, S., Hahn, S. F., & Sokolov, A. P. (2008). Role of Chemical Structure in Fragility of Polymers: A Qualitative Picture. Macromolecules, 41(19), 7232-7238. doi:10.1021/ma801155cSokolov, A. P., Novikov, V. N., & Ding, Y. (2007). Why many polymers are so fragile. Journal of Physics: Condensed Matter, 19(20), 205116. doi:10.1088/0953-8984/19/20/205116Sanchis, M. J., Domínguez-Espinosa, G., Díaz-Calleja, R., Guzmán, J., & Riande, E. (2008). Influence of structural chemical characteristics on polymer chain dynamics. The Journal of Chemical Physics, 129(5), 054903. doi:10.1063/1.295649

Monitoring molecular dynamics of bacterial cellulose composites reinforced with graphene oxide by carboxymethyl cellulose addition

[EN] Broadband Dielectric Relaxation Spectroscopy was performed to study the molecular dynamics of dried Bacterial Cellulose/Carboxymethyl Cellulose-Graphene Oxide (BC/CMC-GO) composites as a function of the concentration of CMC in the culture media. At low temperature the dielectric spectra are dominated by a dipolar process labelled as a beta -relaxation, whereas electrode polarization and the contribution of dc-conductivity dominate the spectra at high temperatures and low frequency. The CMC concentration affects the morphological structure of cellulose and subsequently alters its physical properties. X-ray diffractometry measurements show that increasing the concentration of CMC promotes a decrease of the Ia/Ib ratio. This structural change in BC, that involves a variation in inter- and intramolecular interactions (hydrogen-bonding interactions), affects steeply their molecular dynamics. So, an increase of CMC concentration produces a significantly decrease of the -relaxation strength and an increase of the dc-conductivity.This work was supported by the DGCYT [MAT2015-63955-R]; the Vice-Rectorate for Research of the Pontificia Universidad Catolica del Peril and the National Council of Science, Technology and Technological Innovation of Peru (CONCYTEC/FONDECYT).Sanchis Sánchez, MJ.; Carsí Rosique, M.; Gomez, CM.; Culebras, M.; Gonzales, K.; Gisbert Torres, F. (2017). Monitoring molecular dynamics of bacterial cellulose composites reinforced with graphene oxide by carboxymethyl cellulose addition. Carbohydrate Polymers. 157:353-360. https://doi.org/10.1016/j.carbpol.2016.10.00135336015

Dielectric spectroscopy of natural rubber-cellulose II nanocomposites

[EN] Nanocomposite materials obtained from natural rubber (NR) reinforced with different amounts of cellulose II nanoparticles (in the range of 0 to 30 phr) are studied by dielectric spectroscopy (DS). For comparative purposes the pure materials, NR and cellulose, are also investigated. The dielectric spectra of the nanocomposites exhibit: (a) two overlapped ¿-relaxations associated respectively with the dynamic glass transitions of NR (faster process) and of the lipid present in NR; (b) a ß-relaxation associated with local chain dynamics of cellulose and (c) a relaxation process associated to the presence of traces of water in cellulose. The spectra exhibit conductivity phenomena at low frequencies and high temperatures. The samples were also studied in the dry state. An explanation is given concerning the cellulose effect on the dielectric properties of the dry and wet nanocomposites. © 2010 Elsevier B.V.All rights reserved.The authors gratefully acknowledge CICYT for Grant No. MAT2008-06725-C03-03 and Generalitat Valenciana for Grant No. ACOMP/2010/204.Ortiz Serna, MP.; Díaz Calleja, R.; Sanchis Sánchez, MJ.; Riande, E.; Numes, R.; Martins, A.; Visconte, L. (2011). Dielectric spectroscopy of natural rubber-cellulose II nanocomposites. Journal of Non-Crystalline Solids. 357(2):598-604. doi:10.1016/j.jnoncrysol.2010.06.044S598604357

La Evaluación de Programas de Formación: tipos de planes y algunas cuestiones metodológicas.

Del mismo modo que ha ocurrido en otros contextos educativos, en la Formación para el empleo la Evaluación de Programas se está constituyendo como uno de los instrumentos fundamentales para la mejora de su Calidad. No obstante, en este ámbito inciden una gran cantidad de factores, que deben ser tenidos en cuenta si se desea orientar de forma adecuada la evaluación. (Pérez Carbonell, 1999; Villanueva y Catalá, 1997; Marí, Perales y Villanueva, 1999). Revisarlos, de forma sistemática y exhaustiva, excedería con mucho los limites razonables para esta presentación. Por ello, hemos optado por describir los tipos de planes de evaluación, tomando como criterio la Unidad de Análisis a que se refieren: personas, empresas, sociedad e Instituciones de Formación. Posteriormente, señalaremos los problemas que entendemos que son más relevantes en cuanto a sus implicaciones metodológicas, y que hemos identificado a partir de las diferentes experiencias que hemos venido realizando en este ámbito desde el Dpto. MIDE-UVEG en los últimos años. (Jornet y Suárez, 1997; Perales, 2000; Jornet, Suárez y Perales, 2000)

Structure, dielectric relaxation and electrical conductivity of 2,3,7,8-Tetramethoxychalcogenanthrene-2,3-dichloro-5,6-dicyano-1,4-benzoquinone 1:1 charger-transfer complexes

[EN] 2,3,7,8-Tetramethoxychalcogenanthrenes (5,10-chalcogena-cyclo-diveratrylenes, 'Vn(2)E(2)', E = S, Se) form isotypical 1:1 charge-transfer (CT) complexes with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). X-ray analysis of Vn(2)S(2) . DDQ shows the compound to have a columnar structure with segregated stacks of donors and acceptors. The donors are virtually planar in accordance with a formulation of [Vn(2)E(2)](+)[DDQ](-). Donor cations and acceptor anions are equidistant in their respective stacks, but in each case they inclined to the stacking axis, nevertheless guaranteeing an optimum overlap of the half-filled frontier orbitals which are of pi-type character according to MNDO calculations. Dielectric ac measurements of permittivity epsilon' and loss factor E '' clearly reveal two processes, a dielectric one at low temperatures and a conductive one at high temperatures. The dielectric process can be described by the Havriliak-Negami (HN) and the Kohlrausch-Williams-Watts (KWW) model, and the conductive process by a Debye-type plot. Using these methods, the relevant parameters are evaluated. The de conductivities of polycrystalline samples moulded at 10(8) Pa show a temperature dependence in the plots of ln sigma vs. T-1, which is typical of semiconductors. Two slopes are found; that in the low-temperature region (<285 K) is explained by an easy-path model (intragrain conductivity with low activation energies), whereas in the high-temperature region conduction across the grain boundaries (with higher activation energies) is becoming predominant. The activation energies for the intrinsic conductivities obtained by the ac and de measurements are similar. Despite the columnar structure with segregated stacks, due to stoichiometric oxidation states of the components, the absolute values of conductivity are low ten. 10(-6) S cm(-1) at 293 K), though higher (by a factor of ca. 10(3)) than those of compounds like Vn(2)E(2) . TCNQ with stacks in which donor and acceptor molecules alternate.Behrens, U.; Díaz Calleja, R.; Dötze, M.; Franke, U.; Gunsser, W.; Klar, G.; Kudnig, J.... (1996). Structure, dielectric relaxation and electrical conductivity of 2,3,7,8-Tetramethoxychalcogenanthrene-2,3-dichloro-5,6-dicyano-1,4-benzoquinone 1:1 charger-transfer complexes. Journal of Materials Chemistry. 6(4):547-553. https://doi.org/10.1039/JM9960600547S54755364Behrens, J., Hinrichs, W., Link, T., Schiffling, C., & Klar, G. (1995). SELFSTACKING SYSTEMS, PART 6.1HOST LATTICE FUNCTION OF 2,3,8,9-TETRAMETHOXYDIBENZO[c,e][1,2]-DICHALCOGENINS IN THEIR ELECTRICALLY CONDUCTING IODINE COMPLEXES. Phosphorus, Sulfur, and Silicon and the Related Elements, 101(1-4), 235-244. doi:10.1080/10426509508042522Berges, P., Kudnig, J., Klar, G., Martínez, E. S., & Calleja, R. D. (1989). Elementorganische Verbindungen mit o-Phenylenresten, XVI . 2:1-Komplexe von 2,3,7,8-Tetramethoxychalcogenanthrenen mit Tetracyanethen / Organometallic Compounds with o-Phenylene Substituents, Part XVI 2:1-Complexes of 2,3,7,8-Tetramethoxychalcogenanthrenes with Tetracyanoethene. Zeitschrift für Naturforschung B, 44(2), 211-219. doi:10.1515/znb-1989-0219Hinrichs, W., Berges, P., Klar, G., Sánchez-Martínez, E., & Gunsser, W. (1987). Structure and electrical conductivity of TCNQ-2,3,7,8-tetramethoxychalcogenanthrene complexes. Synthetic Metals, 20(3), 357-364. doi:10.1016/0379-6779(87)90832-0Sánchez Martínez, E., Díaz Calleja, R., Gunsser, W., Berges, P., & Klar, G. (1989). Structure and dielectric relaxation of 2,3,7,8-tetramethoxychalcogenanthrene-TCNQ complexes. Synthetic Metals, 30(1), 67-78. doi:10.1016/0379-6779(89)90642-5Gunßer, W., Henning, J. H., Klar, G., & Martínez, E. S. (1989). Spin Density and Magnetic Susceptibility of Charge-Transfer Complexes with Chalkogenanthrene Donors. Berichte der Bunsengesellschaft für physikalische Chemie, 93(11), 1370-1373. doi:10.1002/bbpc.19890931148G. M. Sheldrick , SHELXTL-PLUS, Release 4.21/0, Siemens Analytical X-Ray Instruments, 1990.Bock, H., Rauschenbach, A., Näther, C., Havlas, Z., Gavezzotti, A., & Filippini, G. (1995). Orthorhombisches und monoklines 2,3,7,8-Tetramethoxythianthren: kleiner Strukturunterschied – große Gitteränderung. Angewandte Chemie, 107(1), 120-122. doi:10.1002/ange.19951070132Bock, H., Rauschenbach, A., Näther, C., Havlas, Z., Gavezzotti, A., & Filippini, G. (1995). Orthorhombic and Monoclinic 2,3,7,8-Tetramethoxythianthrene: Small Structural Difference–Large Lattice Change. Angewandte Chemie International Edition in English, 34(1), 76-78. doi:10.1002/anie.199500761Hinrichs, W., Berges, P., & Klar, G. (1987). Selbststapelnde Systeme, IV 2,3,7,8-Tetramethoxythianthreniumsalze/Selfstacking Systems, Part IV 2.3.7.8-Tetramethoxythianthrenium Salts. Zeitschrift für Naturforschung B, 42(2), 169-176. doi:10.1515/znb-1987-0209Peover, M. E. (1962). 879. A polarographic investigation into the redox behaviour of quinones: the roles of electron affinity and solvent. Journal of the Chemical Society (Resumed), 4540. doi:10.1039/jr9620004540Wheland, R. C., & Gillson, J. L. (1976). Synthesis of electrically conductive organic solids. Journal of the American Chemical Society, 98(13), 3916-3925. doi:10.1021/ja00429a030Zanotti, G., Del Pra, A., & Bozio, R. (1982). Structure of tetraethylammonium–2,3-dichloro-5,6-dicyano-p-benzoquinone. Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 38(4), 1225-1229. doi:10.1107/s0567740882005330Zanotti, G., Bardi, R., & Del Pra, A. (1980). Structure of 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ). Acta Crystallographica Section B Structural Crystallography and Crystal Chemistry, 36(1), 168-171. doi:10.1107/s0567740880002750Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Cleveland, OH, 1977–1978, 58th edn., p. D–178.Sánchez Martínez, E., Díaz Calleja, R., Berges, P., Kudnig, J., & Klar, G. (1989). Structure, electrical conductivity and dielectric relaxation of a 1,2-dimethoxybenzene-tetracyanoethene 1:1 complex. Synthetic Metals, 32(1), 79-89. doi:10.1016/0379-6779(89)90831-xÅsbrink, L., Fridh, C., & Lindholm, E. (1977). HAM/3, a semi-empirical MO theory. I. The SCF method. Chemical Physics Letters, 52(1), 63-68. doi:10.1016/0009-2614(77)85121-xÅsbrink, L., Fridh, C., & Lindholm, E. (1977). HAM/3, a semi-empirical MO theory. III. Unoccupied orbitals. Chemical Physics Letters, 52(1), 72-75. doi:10.1016/0009-2614(77)85123-3Dewar, M. J. S., & Thiel, W. (1977). Ground states of molecules. 38. The MNDO method. Approximations and parameters. Journal of the American Chemical Society, 99(15), 4899-4907. doi:10.1021/ja00457a004Dewar, M. J. S., & Thiel, W. (1977). Ground states of molecules. 39. MNDO results for molecules containing hydrogen, carbon, nitrogen, and oxygen. Journal of the American Chemical Society, 99(15), 4907-4917. doi:10.1021/ja00457a005Åsbrink, L., Fridh, C., & Lindholm, E. (1978). Valence excitation of linear molecules.I. Excitation and UV spectra of N2, Co, acetylene and HCN. Chemical Physics, 27(2), 159-168. doi:10.1016/0301-0104(78)88001-xFridh, C., Åsbrink, L., & Lindholm, E. (1978). Valence excitation of linear molecules. II. Excitation and UV spectra of C2N2, CO2 and N2O. Chemical Physics, 27(2), 169-181. doi:10.1016/0301-0104(78)88002-1Lindholm, E., Bieri, G., Åsbrink, L., & Fridh, C. (1978). Interpretation of electron spectra. III. Spectra of formamide, studied withHAM/3. International Journal of Quantum Chemistry, 14(6), 737-740. doi:10.1002/qua.560140605Starkweather, H. W. (1981). Simple and complex relaxations. Macromolecules, 14(5), 1277-1281. doi:10.1021/ma50006a025Starkweather, H. W. (1990). Distribution of activation enthalpies in viscoelastic relaxations. Macromolecules, 23(1), 328-332. doi:10.1021/ma00203a056Havriliak, S., & Negami, S. (1967). A complex plane representation of dielectric and mechanical relaxation processes in some polymers. Polymer, 8, 161-210. doi:10.1016/0032-3861(67)90021-3J. Ross McDonald , Complex Nonlinear Least Squares Immitance Fitting Program, LEVM6, 1993;Impedance Spectroscopy, Wiley-Interscience, New York, 1987.Williams, G. (1978). Time-correlation functions and molecular motion. Chemical Society Reviews, 7(1), 89. doi:10.1039/cs9780700089Williams, G., & Watts, D. C. (1970). Non-symmetrical dielectric relaxation behaviour arising from a simple empirical decay function. Transactions of the Faraday Society, 66, 80. doi:10.1039/tf9706600080A. R. West , Solid State Chemistry and its Applications, Wiley, Chichester, 1984, ch. 13.Sánchez Martínez, E., Díaz Calleja, R., & Klar, G. (1990). Self-stacking systems 5. Electrical and dielectric properties of 5,5-dibromo-2,3,7,8-tetramethoxyselenanthrene. Synthetic Metals, 38(1), 93-98. doi:10.1016/0379-6779(90)90071-