体积膨胀的稀释作用对聚合物基导电复合材料PTC效应的影响

聚合物基PTC复合材料中,导电填料的体积分数是一个绝缘体-导体的转换开关。理论分析表明,PTC转变区的电阻率突变与渗流曲线在临界体积分数附近的电阻率突变在导电机制上是同一的,聚合物基体体积膨胀的稀释作用对PTC效应有重要影响,在一定的温度范围内(小于PTC/NTC的转变温度),存在着定量的炭黑浓度稀释。 

EFFECT OF DILUTION DUE TO THERMAL VOLUME EXPANSION ON PTC EFFECT OF THE CONDUCTIVE POLYMER COMPOSITES

The study of the quantitative contribution of the thermal volume expansion to the positive temperature coefficient (PTC) switch effect of fine particles filled polymer composites in the carbon black polyethylene(CB PE) system is reported. The decrease of room temperature resistivity with the increase of CB loading level (CB volume fractions at room temperature) experimentally obtained was fitted by General Effective Medium (GEM) equation in order to establish the mixing rule of the system. A dilution of the CB volume fraction due to the thermal volume expansion of the composites is estimated and "real" CB volume fractions of a certain loading level at different temperatures are thus found. Being treated equivalent to the loading levels, the "real" CB volume fractions at high temperatures are used to replace the volume fraction in the above GEM equation. By using this model, the contribution of thermal expansion of matrix to the jump like PTC switch transition of the composites is quantitatively estimated. The theory and experiment have proved that the conductive mechanism of abrupt resistivity increase at PTC transition range is equivalent as abrupt resistivity increase at the percolation curve close to the critical volume fraction.