Conductive polymer switching mechanism for high power current-limiting applications

Investigations on heat-generation stability and PTC effects of self-heating cement composites under diverse temperature conditions

PTC (Positive Temperature Coefficient) effects of grain boundaries in a normal PTC thermistor and in a reduced and reoxidized one were directly measured by A. C. complex impedance analysis. The PTC effect and capacitance of a single grain boundary were different with each grain boundary and the PTC effect of the grain boundary with a smaller capacitance tended to be larger. It was considered that the difference in the thickness of the depletion layer of the Schottky barrier in the grain boundary caused the difference in the PTC effect and the capacitance of each grain boundary.

Conductive polymer composite (CPC) is a very significant research topic in the area of self-regulating heating. It acts in self-regulated heating mode due to its positive temperature coefficient (PTC) effect. PTC effect is the consequence of breakup of conductive paths formed in CPC due to heat up of polymer composite. Currently a good number of researchers are going on conductive polymer composites. In this paper, the important aspects of conductive polymer composites; such as: conduction process, positive temperature co-efficient effect, negative temperature co-efficient etc has been analyzed. Moreover, a summary of the researches conducted by researchers in the fields of conductive polymer composites by employing hybrid fillers has also been discussed.

Polymeric positive temperature coefficient (PTC) materials have been prepared by incorporating carbon black (CB) into two different polymer matrices, crystalline high density polyethylene (HDPE) and amorphous polystyrene (PS). The effects of thermal volume expansion on the electrical properties of conductive polymer composites were studied. The volume fraction of conductive particles behaves like a switch from insulator to conductor in the polymeric PTC composite. Our mathematical model and experimental model have proved that the abrupt resistivity increase at PTC transition range and at the percolation curve close to the critical volume fraction for both polymeric PTC composites have the same conductive mechanism. The thermal expansion is one of the key factors responsible for the PTC effect and can be seen by comparing the PTC transition curves from model predictions and experiment. Furthermore, the model predicts PTC curves of CB/PS composite more successfully than it does for the CB/HDPE composite, and the reasons for this are also discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 3078–3083, 2007

The positive temperature coefficient (PTC) effects of carbon black (CB)‐filled semicrystalline and amorphous ethylene–propylene–diene terpolymer (EPDM) composites were studied. The semicrystalline EPDM/CB composite exhibited a low PTC effect followed by a pronounced negative temperature coefficient (NTC) effect, while the amorphous EPDM/CB composite exhibited only an NTC effect. By the effect of γ‐ray irradiation, not only was the NTC effect of the composites eliminated, but also a high PTC effect appeared. The PTC intensity reached as high as six orders of magnitude even for an amorphous EPDM/CB composite and the PTC transition temperature decreased with the irradiation dose. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1571–1574, 2001

Electrical conductivity of carbon black–polyethylene composites: Experimental evidence of the change of cluster connectivity in the PTC effect

Studies on the PTC/NTC effect of carbon black filled low density polyethylene composites

The effect of conductive network on positive temperature coefficient behaviour in conductive polymer composites

Temperature Coefficient of Resistance (TCR) is the important parameter in Electromigration Test of the metal reliability. The physical dimensions of the metallization can be affected by temperature. The coefficient of thermal expansion for a sample of the metallization can be used to approximate its change in volume given and a change in temperature. An object of uniform cross section will have a resistance proportional to its length and inversely proportional to its cross-sectional area, and proportional to the resistivity of the material. TCR is a fractional change in resistance per unit change in temperature at a specified temperature. In order to get the most reliable metal lines, lower TCR value is needed. Normally lower TCR value can be obtained if the grain size of the metal line is smaller. In this study, two types of metal process flows which are known as hot and cold metal is evaluated using TCR measurement. The hot and cold metal process use the same source of AlSiCu but the preparation for deposition is a bit different in which the hot metal process used temperature setting of 300oC, while the cold metal process the temperature is set at 175oC. From the result it is found that the metallization sheet resistance is linearly increase with increasing temperature and the TCR value also decrease with smaller line widths. From the FIB micrograph picture it is found that lower process temperature will give smaller grain size and lower TCR value.

In this article, the positive temperature coefficient (PTC) and interaction based on low‐density polyethylene (LDPE) filled with the loading of graphite (G) powder have been investigated. The dependence of the room temperature resistivity on filler content showed the significant decrease. The PTC behavior enhanced with increasing graphite content but this was not always the case. The maximum PTC effect was observed in LDPE/G composites (G, 45 wt %) with the relatively low room temperature resistivity. The thermal behavior was measured by differential scanning calorimetry (DSC). The structure characteristic for LDPE/G composites was examined by X‐ray diffraction (XRD), field‐emission scanning electron microscopy (SEM), and stress–strain test. The fact was revealed that the slight interaction between LDPE matrix and graphite may lead to change the thermal‐electric properties of the PTC materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

The present article is concerned with the temperature‐conductivity characteristics of blends consisting of polyisothianaphthene (PITN) particles and a soluble poly(3‐hexylthiophene) (P3HT). PITN was synthesized by direct conversion of 1,3‐dihydroisothianaphthene (DHITN) monomer using N‐chlorosuccinimide (NCS) as an oxidation/dehydrogenation reagent. The high conductivity and thermal stability of the doped and dedoped PITN were confirmed. Microscopic investigation by scanning electron microscopy (SEM) showed that the as‐prepared PITN exhibited diversified shapes and sizes, with large rectangular particles having an average size of 2 ∼ 5μm and fine round particles ranging from 0.1 to 0.3 μm. The PITN particles were blended with the chemically synthesized P3HT as a high conductivity component to improve the conductivity and simultaneously maintain the positive temperature coefficient (PTC) effect of the original P3HT near its melting point. The temperature‐conductivity characteristics for PITN‐P3HT blends with various PITN contents showed that a blend having both a high conductivity (nearly 3 ∼ 4 orders higher than that of the original P3HT) and a good PTC intensity could be obtained with a PITN content of 20 ∼ 25%. The different temperature‐conductivity behavior of P3HT blends filled with PITN as compared to other conducting particles, for example, carbon black, was explained by its unique dispersion structure due to a relatively higher adhesive interaction of PITN particles with the P3HT matrix during the precipitation process. The results from heating recycles revealed that the PTC effect of PITN‐P3HT blends was not just related to the conductivity decrease of the P3HT matrix, arising from the conformational change of the conjugated backbone during the melting, but also to the dilution effect of the conducting percolation network due to the mobility of PITN particles induced by the viscosity decrease of the P3HT matrix. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1848–1854, 2005

Conductive polymer composites have been applied in temperature sensing owing to its resistance response to temperature change. In this work, composites with short carbon fibers (CFs) filled in silicon rubber (SR) were 3D printed. The positive temperature coefficient (PTC) effect of the composite resistance behaved anisotropically due to the CFs’ orientation, where the PTC intensity was lower when tested along the CFs’ orientation than that along other directions. The composites owned an excellent PTC effect reproducibility at the temperature of 25 ~ 100 °C. In-situ observation shows that the CFs in the composites shifted about 2.62 ± 1.05 μm when the temperature increased from 25 °C to 80 °C. The resistance creep under isothermal aging treatment reveals that the composites could keep their resistance relatively stable at the isothermal aging of 20 ~ 80 °C. The mechanical loads could help the crept resistance to recover to its original value very quickly, which was referred to resistance memory effect (RME) in this article. CF/SR composite was finally connected into circuits as thermistor and temperature sensor, which verified a potential application for temperature sensing.

The linear viscoelastic behavior and electrical conductivity of high-density polyethylene (HDPE) filled with stainless steel fibers (SSF) were investigated and compared with those of carbon black (CB) filled HDPE composites system.It is found that CB/HDPE composites show two electrical conductivity percolation values (φ c1 and φ c2 ) and a wide percolation range.However,SSF/HDPE composites present an extremely low threshold of the electrical conductivity percolation (only 0.3 vol%) and a narrow percolation range.Only one conductivity percolation value (φc) was observed.The speciality of conductivity percolation behavior of SSF/HDPE composites owes to the formation of conducting channels of SSF/HDPE composites.It is well recognized that the rheological percolation threshold is identical to the percolation threshold of electrical conductivity for CB/HDPE composites.Whereas,for SSF/HDPE composites,dynamics storage modulus (G') becomes almost independent of frequency in the low frequency region as the SSF loading increases up to 4.8 vol%,suggesting an onset of solidlike behavior in SSF/HDPE composites.By plotting G' versus SSF loading,the rheological threshold is determined as 4.8 vol%,which is much lower than the percolation threshold of electrical conductivity,i.e. 0.3 vol%.Additionally,the positive temperature coefficient (PTC) effect was measured for SSF/HDPE and CB/HDPE composites.It reveals that the conductivity channels formed by SSF show a higher stability than those formed by CB particles in HDPE matrix.The difference in the percolation threshold and the stability of conductivity channels are understood in terms of the larger L/D of SSF and the particular conductive mechanism of SSF/HDPE composites

The effect of temperature on the resistivity of Sn–Pb alloy-loaded PS composites was studied. The composites have distinctive positive temperature coefficient (PTC) effects with high PTC intensity, abrupt PTC transition, etc. According to SEM and EDAX analyses, the morphology of the alloy particles in the composites remained unchanged as the temperature reached the melting point of the alloy, while the alloy dispersion changed. The viscosity of the composites decreased sharply when the alloy melted. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 756–763, 2000

Composite materials based on ultrahigh-molecular-weight polyethylene (UHMWPE)–low- molecular-weight polyethylene (LMWPE) and carbon black (CB) particles were prepared by a gelation/crystallization process from dilute solution. The method was developed to obtain composite materials with an improved and reproducible positive temperature coefficient (PTC) effect. Drastic improvement of the PTC effect was achieved when specimens with a LMWPE/UHMWPE composition of 9/1 containing 13 wt% CB were treated at 170 °C without restraint before measurement. The maximum PTC intensity, defined as the ratio of the maximum resistivity to the resistivity at room temperature, was about 5 orders of magnitude, which equals that of the LMWPE-CB system prepared by a kneading method. Interestingly, electrical resistivity during the heating-cooling process showed good reproducibility in the temperature range 30–190 °C, but has never been reported before even for cross-linked LMWPE-CB compostie. Scanning electron micrographs revealed that CB particles were dispersed in the LMWPE matrix, but not on the UHMWPE fibrils. It turns out that the network structure of UHMWPE, with a very low melt index, plays an important role in removing the negative temperature coefficient effect usually observed for the LMWPE-CB system and in ensuring the quality and the reproducibility of the PTC effect.