Two-Step Percolation in Polymer Blends Filled with Carbon Black

Zhang, Ming Qiu; Yu, Gang; Zeng, Han; Zhang, Hai Bo; Hou, Yan Hui

doi:10.1021/ma9806918

Cited by 146 publications

(96 citation statements)

References 7 publications

(9 reference statements)

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“…Faster increase of r than that caused by thermal expansion, DL/L 0 , can be caused by change of the morphological structure of the polymer matrix in the vicinity of T m , that destroys the conductive structure. The creation of additional amorphous phase during melting of the crystalline regions leads to interaction between the polymer melt and the iron conductive chains and promotes the formation of additional gaps between the filler particles [39], as well as the agglomeration of the particles [27], that gives additional contribution to the increase of resistivity.…”

Section: Thermal Expansion Of the Compositesmentioning

confidence: 99%

PTC effect and structure of polymer composites based on polyethylene/polyoxymethylene blend filled with dispersed iron

Mamunya

Muzychenko

Lebedev

et al. 2006

Polymer Engineering & Sci

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The temperature dependence of resistivity, structure, and thermal expansion of composites based on polyethylene/polyoxymethylene (PE/POM) blends filled with dispersed iron (Fe) have been studied. The dependence of conductivity on filler content shows percolation behavior, with the values of the percolation thresholds equal to 21 vol% for PE‐Fe, 24 vol% for POM‐Fe, and 9 vol% for the filled blend PE/POM‐Fe, with two‐step character of the conductivity curve. The evolution of structure of the composite PE/POM‐Fe demonstrates transition from polymer matrix POM‐Fe, with inclusions of PE through cocontinuous phases of both POM‐Fe and PE, to PE matrix, with inclusions of POM‐Fe. Such a structure occurs due to localization of the filler only in one of the polymer phases, namely in POM. Measurements of the coefficient of thermal expansion α show the presence of two values of α: higher value (equal to α of PE) and lower value (equal to α of POM‐Fe), the transition between them corresponding to the structure with cocontinuous phases. The PE/POM‐Fe composites demonstrate double‐positive temperature coefficient (PTC) effect, with the presence of two transitions and a plateau between them. In such a system, two contributions to the PTC effect coexist: the first contribution originates from the thermal expansion of the nonconductive PE phase with higher value of the coefficient α, which leads to the break of the continuity of the conductive POM‐Fe phase; the second contribution originates from the break of the conductive structure of the filler inside the POM‐Fe phase because of the morphological changes in the vicinity of the melting temperature of POM. The double PTC effect is explained in terms of these two processes (thermal expansion and melting). POLYM. ENG. SCI., 47:34–42, 2007. © 2006 Society of Plastics Engineers

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Section: Thermal Expansion Of the Compositesmentioning

confidence: 99%

PTC effect and structure of polymer composites based on polyethylene/polyoxymethylene blend filled with dispersed iron

Mamunya

Muzychenko

Lebedev

et al. 2006

Polymer Engineering & Sci

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“…achievement of equilibrium resistivity that approaches the value of filler itself. 6 Appearance of such a terrace-like part on a percolation curve provides a wider processing window for composite manufacturing.). It is believed that effective concentration of filler in the filler-rich phase, structural continuity, and melting behavior of this phase determine the PTC effect of conductive polyblends.…”

Section: Introductionmentioning

confidence: 99%

Effect of filler treatment on temperature dependence of resistivity of carbon-black-filled polymer blends

Yu¹,

Zhang²,

Zeng³

et al. 1999

J. Appl. Polym. Sci.

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Polyblends prove to be able to provide more possibilities for tailoring conductive polymer composites in comparison with individual polymer systems. Accordingly, ethylene-vinyl acetate-low-density polyethylene (EVA-LDPE) filled with carbon black (CB) was prepared in this study as a candidate for positive temperature coefficient (PTC) material. In consideration of the fact that CB distribution plays the leading role in controlling a composite's conduction behavior, chemical treatment of CB was applied to reveal its influence on percolation and the PTC effect. It was found that titanate coupling agent treatment facilitated sufficient distribution of CB in LDPE phase, leading to lower resistivity and a squarer PTC curve. Composites filled with nitric-acid-treated CB exhibited specific temperature dependence of resistivity as a result of the heterogeneous dispersion of CB at the interface of EVA-LDPE, which might provide the materials with a new function.

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“…Hereinafter the response kinetics of CB/WPU composites is also treated by the same approach. That is, electrical responses of the composites against chloroform vapor were measured at different temperatures (20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30)(31)(32)(33)(34)(35) C) and then the response times (define as the times to reach half of the maximum responsivity, see Figure 8) were determined, giving a series of Arrhenius plots and the corresponding activation energies, E a ( Figure 9). The lowest E a value of CB/WPU-3 can be explained by the greatest mobility of CB par- Vapor Sensitivity of WPU Based Composites ticles provided by the swollen WPU-3, which contains soft segments with the highest flexibility.…”

Section: Rate Of Responsementioning

confidence: 99%

Effect of Soft Segments of Waterborne Polyurethane on Organic Vapor Sensitivity of Carbon Black Filled Waterborne Polyurethane Composites

Zhao¹,

Fu²,

Zhang³

et al. 2006

Polym J

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ABSTRACT:In the present work, three types of waterborne polyurethane (WPU) were synthesized, in which poly(ethylene oxalate glycol), poly(propylene oxide) and poly(tetramethylene ether glycol) acted as the soft segments, respectively. The WPUs were then compounded with carbon black (CB) to fabricate gas sensing composites. By studying the composites' resistance variation in different solvent-vapors, it was found that the structures of the WPUs remarkably affected the composites' response behaviors. Both polarity and flexibility of the soft segments of WPU determine to a great extent the solvent-polymer interaction and preferential localization of solvent and fillers, resulting in different magnitudes of resistance increase and rates of response. Recently carbon black (CB) filled polymer composites have been exploited for the fabrication of chemical sensors.1,2 When being exposed to organic vapors, the composites exhibit a drastic increase in their electrical resistivity because matrix swelling induced by solvents absorption expands the inter-filler gap.3,4 Removal of the stimuli leads to desorption of the vapors and a decrease in the composites' resistance back to the original value. On the basis of this feature, therefore, low cost organic solvent leak detectors and ''electronic noses'' can be manufactured. [5][6][7] In the authors' lab, waterborne polyurethane (WPU) was employed to be mixed with CB for preparing gas sensing composites.8 As WPU is a segmented polymer consisting of the alternating sequence of long non-polar soft segments and short polar hard segments that constitute a unique microphase separation structure, its composites with CB exhibit widespectrum responsivity to both low/non-polar and polar solvents. [9][10][11][12] It was found that the segmented microstructure of WPU greatly influenced the relationships between solvent adsorption behavior and electrical resistance variation of WPU based composites. 13In this context, it is worth studying the effect of soft segments on vapor sensitivity of CB/WPU composites, which might lead to optimization of the polymer's microstructure and hence the sensing performance of the composites. Accordingly, three kinds of WPU were synthesized in the present work, in which only the soft segments are different. These soft segments were selected because of their distinct structures and features. As shown in Table I, poly(tetramethylene ether glycol) (PTMEG) possesses the highest flexibility because there is no side groups on its skeleton, while poly(ethylene oxalate glycol) (PEOG) has the lowest flexibility due to the strong interaction between the ester groups. In regard to polarity, however, the above rank has to be reversed. By comparing electrical response habits of the composites based on these WPUs in benzene (non-polar solvent), chloroform (low polar solvent) and acetone (polar solvent) vapors, it is believed that the influence of WPU microstructure on composites sensitivity would be revealed. EXPERIMENTAL MaterialsAnalytically pure ethylenediamine anhydrou...

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Two-Step Percolation in Polymer Blends Filled with Carbon Black

Cited by 146 publications

References 7 publications

PTC effect and structure of polymer composites based on polyethylene/polyoxymethylene blend filled with dispersed iron

PTC effect and structure of polymer composites based on polyethylene/polyoxymethylene blend filled with dispersed iron

Effect of filler treatment on temperature dependence of resistivity of carbon-black-filled polymer blends

Effect of Soft Segments of Waterborne Polyurethane on Organic Vapor Sensitivity of Carbon Black Filled Waterborne Polyurethane Composites

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