An experimental study of dynamic behaviour of graphite polycarbonatediol polyurethane composites for protective coatings

Segmented polycarbonatediol polyurethane (PUPH) has been synthesized and modified with different amounts of graphite conductive filler (from 0 to 50 wt%). Thermal and dynamical thermal analysis of the composites clearly indicates changes in the polyurethane relaxations upon addition of graphite. Broadband dielectric spectroscopy has been used to study the dielectric properties of the (PUPH) and one composite in the frequency range from 10−2 to 107 Hz and in the temperature window of −140 to 170 ◦C. Relaxation processes associated with different molecular motions and conductivity phenomena (Maxwell–Wagner–Sillars and electrode polarization) are discussed and related to the graphite contentWe acknowledge the financial support of the Ministry of Finances and Competitiveness through the Grant CDS2010-0044 belonging to the "Consolider-Ingenio Programme" and for the Grant MAT2012-33483. The authors thank UBE Chem Eur for the PCD supply for this work.Gómez, C.; Culebras, M.; Cantarero Saez, A.; Redondo Foj, MB.; Ortiz Serna, MP.; Carsí Rosique, M.; Sanchis Sánchez, MJ. (2013). An experimental study of dynamic behaviour of graphite polycarbonatediol polyurethane composites for protective coatings. Applied Surface Science. 275:295-302. https://doi.org/10.1016/j.apsusc.2012.12.108S29530227

Relaxational study of poly(vinylpyrrolidone-co-butyl acrylate) membrane by dielectric and dynamic mechanical spectroscopy

[EN] A poly(vinylpyrrolidone-co-butyl acrylate) (60VP-40BA) membrane is synthesized as a tractable and hydrophilic material, obtaining a water-swelling percentage around 60%. An investigation of molecular mobility by means of differential scanning calorimetry, dynamic mechanical analysis and broadband dielectric relaxation spectroscopy (DRS) is fulfilled in the dry membrane. Dielectric and viscoelastic relaxation measurements are carried out on the 60VP-40BA sample at several frequencies between -150 and 150 degrees C. The dielectric spectrum shows several relaxation processes labelled gamma, beta and alpha in increasing order of temperature, whereas in the mechanical spectrum only the beta and alpha relaxation processes are completely defined. In the dielectric measurements, conductive contributions overlap the alpha-relaxation. The apparent activation energies have similar values for the beta-relaxation in both, the mechanical and the dielectric measurements. The beta process is a Johari-Golstein secondary relaxation and it is related to the local motions of the pyrrolidone group accompanied by the motion of the segments of the polymer backbone. The gamma process is connected with the butyl unit's motions, both located in the side chains of the polymer.BRF, MC, PO and MJS are grateful to CICYT for grant MAT2012-33483. FG and JMG thank the Spanish Ministerio de Economia y Competitividad-FEDER (MAT2011-22544) and the Consejeria de Educacion-Junta de Castilla y Leon (BU001A10-2).Redondo Foj, MB.; Carsí Rosique, M.; Ortiz Serna, MP.; Sanchis Sánchez, MJ.; García, FC.; García. José Miguel (2013). Relaxational study of poly(vinylpyrrolidone-co-butyl acrylate) membrane by dielectric and dynamic mechanical spectroscopy. JOURNAL OF PHYSICS D-APPLIED PHYSICS. 46(29):295304-1-295304-12. https://doi.org/10.1088/0022-3727/46/29/295304S295304-1295304-12462

Electrical conductivity of natural rubber cellulose II nanocomposites

[EN] Nanocomposite materials obtained from natural rubber (NR) reinforced with different amounts of cellulose II (cell) nanoparticles (in the range of 0 to 30 phr) are studied by dielectric spectroscopy (DS) in a broad temperature range (¿150 to 150 °C). For comparative purposes, the pure materials, NR and cell, are also investigated. An analysis of the cell content effect on the conductive properties of the nanocomposites was carried out. The dielectric spectra exhibit conductivity phenomena at low frequencies and high temperatures: Maxwell¿Wagner¿ Sillars (MWS) and electrode polarization (EP) conductive processes were observed in the nanocomposite samples.We thank Professor Regina Nunes of the Instituto de Macromoleculas Eloisa Mano (Universidade Federal do Rio de Janeiro) for providing us the NR and NR-cell samples. This work was financially supported by DGCYT through grant MAT2012-33483.Ortiz Serna, MP.; Carsí Rosique, M.; Redondo Foj, MB.; Sanchis Sánchez, MJ. (2014). Electrical conductivity of natural rubber cellulose II nanocomposites. Journal of Non-Crystalline Solids. 405:180-187. https://doi.org/10.1016/j.jnoncrysol.2014.09.026S18018740

Conductivity and time-temperature correspondence in polar viscoelastic liquids

This work is focused on the conductivity study of viscoelastic liquids, taking as a model poly(2,3-dimethoxybenzyl methacrylate). Each isotherm, displaying the conductivity in the frequency domain, shows a plateau in the low frequency region, representing the dc conductivity. The covered frequency range by the plateau increases with the temperature. The frequency corresponding to the end of the plateau, ωc, marks the onset of the ac conductivity, which correspond in increasing order of frequency to Maxwell-Wagner-Sillars, glass-rubber transition and secondary relaxations. The contributions of the relaxation processes to the ac conductivity in the wholly frequencies range were analyzed. The time-temperature correspondence principle holds for the reduced ac conductivity. However, this principle does not hold for the components of the complex dielectric permittivity due, among other things, to the different temperature dependences of each dipolar relaxation processes. Analogueies and differences between the conductivity behavior of viscoelastic liquids and disordered inorganic solids are discussed.Peer Reviewe

Conductivity and Time–Temperature Correspondence in Polar Viscoelastic Liquids

This work is focused on the conductivity study of viscoelastic liquids, taking as a model poly­(2,3-dimethoxybenzyl methacrylate). Each isotherm, displaying the conductivity in the frequency domain, shows a plateau in the low frequency region, representing the dc conductivity. The covered frequency range by the plateau increases with the temperature. The frequency corresponding to the end of the plateau, ω_<i>c</i>, marks the onset of the ac conductivity, which correspond in increasing order of frequency to Maxwell–Wagner–Sillars, glass–rubber transition and secondary relaxations. The contributions of the relaxation processes to the ac conductivity in the wholly frequencies range were analyzed. The time–temperature correspondence principle holds for the reduced ac conductivity. However, this principle does not hold for the components of the complex dielectric permittivity due, among other things, to the different temperature dependences of each dipolar relaxation processes. Analogueies and differences between the conductivity behavior of viscoelastic liquids and disordered inorganic solids are discussed

Study of the thermal, dielectric and mechanical properties of poly(methyl methacrylate-co-(1,4,7,10-tetraoxacyclododecan-2-yl)methyl Methacrylate) Membranes

Euromembrane Conference 2012DGCYT and CAM through the Grant MAT2008-06725-C0