Here we report a first analytical approach to determine the spectral dependence of the complex permittivity function of molecular and macromolecular ionic conductors in the interfacial layers formed ...by electrode polarization effects. We show that a previous model of electrode polarization effects that was successfully applied for describing the dielectric behavior of ionic liquids (Serghei, A.; Tress, M.; Sangoro, J. R.; Kremer, F. Electrode polarization and charge transport at solid interfaces. Phys. Rev. B 2009, 80, 184301 ) can be now generalized and applied for polymer/ionic liquid blends as well as for poly(ionic liquid)s. The determined dielectric function of the interfacial layers reveals a dramatic change in the charge transport process manifested by a large decrease in conductivity. Our approach brings the first evidence for a relaxation peak detected in the dielectric loss of the interfaces, which is attributed to an exchange process between the interface and the bulk. This study gives new insights into the mechanism of charge transport at interfaces and could thus contribute to a better correlation between the dielectric properties of ion conducting materials and their electrochemical behavior at interfaces.
Purpose
We investigate the effects of 12-week interval training of moderate- or high-intensity exercise on blood lipids and plasma levels of adiponectin.
Methods
Thirty-four obese adolescent females ...age = 15.9 ± 0.3 years; BMI and BMI-
Z
-score = 30.8 ± 1.6 kg/m
2
and 3 ± 0.3, respectively, were randomized to high-intensity interval training (HIIT,
n
= 11), moderate-intensity interval training (MIIT,
n
= 11), or a control group (CG,
n
= 12). Maximal oxygen uptake (
V
.
O
2
peak
), maximal aerobic speed (MAS), plasma lipids and adiponectin levels were measured in all subjects before and after training.
Results
Following the training program, in both training groups, body mass, BMI-
Z
-score, and percentage body fat (% BF) decreased, while
V
.
O
2
peak
and MAS increased. Low-density lipoprotein cholesterol, high-density lipoprotein cholesterol, and adiponectin levels were positively altered (−12.6 and −7.4 %; 6.3 and 8.0 %; 35.8 and 16.2 %; high to moderate training program, respectively). Waist circumference, triglyceride and total cholesterol decreased only in HIIT group (−3.5; −5.3 and −7.0 %, respectively, in all
P
< 0.05). Significant decrease in the usual index of insulin resistance (HOMA-IR) occurred in HIIT and MIIT groups (−29.2 ± 5.3 and −18.4 ± 8.6 %, respectively;
P
< 0.01).
Conclusion
The results show that HIIT positively changes blood lipids and adiponectin variables in obese adolescent girls, resulting in improved insulin sensitivity, as attested by a lower HOMA-IR, and achieving better results compared to moderate-intensity exercise.
Dielectric measurements were performed on Poly(lactic acid) (PLA) polymer, Poly(lactic acid)/Poly(butylene succinate) (PLA/PBS) blend matrix and its green composite reinforced with Jute fibers in ...temperature range from 20 to 140 °C and frequency range from 10
−1
Hz to 1 MHz. Thermal analyses based on differential scanning calorimetry technique have evidenced different thermal transitions of the semi-crystalline polymer occurred for PLA one. Addition of PBS into PLA polymer enhanced its crystallinity. However, the presence of Jute fibers in the green composite material lowered such effect and increased the PLA polymer glass transition temperature, T
g
. These could be attributed to the PBS contribution into the Jute fibers/blend matrix interactions. Accordingly, dielectric analyses have revealed the presence of three relaxation processes for PLA polymer. These were identified to the α mode relaxation, the dc conductivity effect and the Maxwell–Wagner–Sillars (MWS) interfacial polarization effect. The latter effect was attributed to the accumulation of charges at the crystalline phase/amorphous phase interfaces of PLA polymer. Two additional dielectric relaxations appeared for PLA/PBS blend matrix. These were associated with β relaxation and interfacial polarization effect originating from PLA polymer and the semi-crystalline character of PBS polymer, respectively. The incorporation of Jute fibers into the PLA/PBS blend matrix gave rise to other dielectric relaxations associated with the water dipoles and interfacial (Jute fibers/blend matrix) polarization effects. Analysis of dielectric relaxations at high temperature above the glass transition temperature using the Havriliak–Negami model allowed probing Jute fibers/blend matrix interactions. Adhesion mechanism occurred in the studied green composite was determined by vibrational analysis based on FT-IR technique.
In the present work, the dielectric properties of nanocomposites based on poly(styrene-Co-2-ethyl hexylacrylate) copolymer (StHA) and cellulose nanocrystals (CNCs) and γ-methacryloxypropyl ...triethoxysilane (MPS) as a coupling agent were investigated. Four relaxation processes were detected: the β relaxation, the α relaxation, the electrode polarization and the ionic conduction phenomenon. These two later were identified with the real part ε' and the imaginary part ε” of the dielectric permittivity slopes. Moreover, the electrode polarization was spotted using the first derivative of the real part of the dielectric permittivity. The activation energy EA for the β relaxation, the strength parameter D for the α relaxation and the relaxation strength Δε showed a threshold value of 4% in weight of CNC. Variations were explained with attractive and repulsive cellulose-cellulose and cellulose-copolymer interactions. The electrical study confirmed the dielectric results indicating the higher conductivity for the nanocomposite with 4%w.t of CNC. This work provided additional evidence of the formation of a rigid percolation network via hydrogen bonding for nanocomposites based on CNCs.
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•Styrene hexylacrylate copolymer/cellulose nanocomposites are investigated.•The α and the β relaxation process are affected by cellulose nanocrystals content.•The use of the derivative formalism is a very powerful tool in dielectric studies.•The higher reinforcing effect of the cellulose nanocrystals is obtained at 4%w.t.
This work deals with the dielectric properties of silane treated pineapple leaf fiber and kenaf fiber reinforced phenolic hybrid composites. The aim of the present paper is to investigate the effect ...of silane treatment on the pineapple leaf fiber–kenaf fiber/matrix interfacial adhesion using the dielectric relaxation spectroscopy in the frequency range from 0.1 Hz to 1 MHz and temperature range from 50 to 180℃. Our hybrid composites were fabricated by hand lay-up method at 50% total fiber loading. All the results obtained were discussed in terms of dynamic molecular and interfacial process. Two interfacial polarizations identified as the Maxwell–Wagner–Sillars effect are observed. We note that silane treatment improved the interfacial adhesion between pineapple leaf fiber/kenaf fiber and phenolic resin and it will help to develop high performance kenaf fiber/pineapple leaf fiber reinforced polymer composites for industrial applications. In fact, as known, the silane treatment developed hydrophobic nature in pineapple leaf fiber and kenaf fiber which is very positive for fiber/matrix compatibility.
The thermoelectric behavior, mechanical properties and microstructures of bulk n-type Si80Ge20 samples prepared by mechanical alloying (grain size <200nm) and hot pressing are investigated. The ...measured figure of merit (ZT) is approximately 1 at 800°C. Young's modulus measured by acoustic echography, four point bending test and nanoindentation is estimated to be ∼143GPa for dense sample. Bulk hardness, determined by nanoindentation is 14.5GPa (at 0.1N load). Fracture toughness estimated by Vickers indentation method assuming Palmqvist cracks system is around 1MPa√m.
Natural rubber (NR) isolated from Hevea Brasiliens and reinforced with different amounts of cellulose nanowhiskers (extracted from the rachis of date palm tree) was investigated using differential ...scanning calorimetry and dielectric spectroscopy in the frequency range 0.1 Hz to 1 MHz, and the temperature range −80 to 200 °C. The experimental dielectric data were analysed within the formalisms of dielectric permittivity, complex conductivity and complex modulus. The results were discussed in terms of dc conductivity, interfacial polarization and electrode polarization. The paper aims to investigate especially the electrode polarization observed at low frequency and/or high temperature (LF/HT). It is exhibited that the understanding of the frequency space charge relaxation behaviour trapped close to the material/electrode interface will help one to elucidate the charge dynamics in the quasi static range. So charge carrier concentration and mobility in the sample at high temperature can be evaluated through the electrode polarization modeling of broadband dielectric spectroscopy data.
•Adding nanocellulose in latex led to composite with superior dielectric properties.•Dipolar relaxation, interfacial and electrode polarization are modeled.•The nanocomposites fragility parameters are estimated from relaxation process.•Close to material/electrode interface, charge dynamics are elucidated.•Charge carrier concentration and their mobility in nanocomposites are evaluated.
Fused filament fabrication (FFF) is an additive manufacturing (AM) process that provides physical objects commonly used for modeling, prototyping and production applications. The major drawback of ...this process is poor mechanical property due to the porous structure of final parts. This process requires careful management of coalescence phenomenon. In this paper, the major influencing factors during the FFF processing of poly(lactic acid) (PLA) were investigated experimentally and with a numerical model. It has been shown that the polymer temperature has a significant effect on the rheological behavior of PLA, especially on the adhesion of the filaments. An experimental set-up has been placed in the machine to have the cyclic temperature of the filament. A variation of the polymer temperature influences process parameters such as feed rate, temperature of the nozzle and temperature of the platform. The results showed that the amount of polymeric coalescence (neck growth) rises when increasing the feed rate, the nozzle temperature, and the platform temperature. A model to predict the neck growth is proposed. It predicts a lower amount of neck growth value than obtained experimentally. This difference has been explained as the effect of other phenomena, such as polymer relaxation time, pressure of the nozzle and especially cyclic temperature which is not taken into account in the model.
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