表层氟化温度对聚乙烯中空间电荷积累的影响

在实验室反应釜中于不同的温度(35 ℃, 55 ℃和70 ℃) 下, 以氟气体积浓度为12.5%的氟/氮混合气对热压制备的聚乙烯(PE) 片状试样(厚约0.8 mm) 进行了相同时间(2 h) 的表层氟化改性. 利用压力波法研究了氟化温度对PE中空间电荷积累的影响. 结果显示, 随着氟化温度的提高直流高压作用下的氟化试样中的空间电荷积累明显减少, 这个70 ℃的氟化试样中几乎没有空间电荷. 衰减全反射红外分析表明, 氟化引起了试样表层化学组成的本质变化及氟化度随氟化温度的明显提高. 接触角测量与表面能计算间接地表明了这些氟化层有显著增大的介电常数. 开路热刺激放电电流测量进一步揭示了这些氟化层 不同的电荷捕获特性, 及随着氟化温度的提高氟化层对化学杂质从半导性电极向PE扩散的增强的阻挡特性, 因此表明氟化层中自由体积的相应减小. 表层自由体积的减小对抑制空间电荷的积累, 比介电常数的增大和电荷陷阱的变化起到更加显著的作用.

Influence of surface fluorination temperature on space charge accumulation in polyethylene

Polyethylene（PE） discs prepared by hot-pressing,each with a thickness of 0.8 mm,are surface fluorinated in a laboratory vessel by an F₂/N₂ mixture containing 12.5%F₂ by volume at different temperatures of 35,55,and 70℃for the same time of 2 h.The influence of fluorination temperature on space charge accumulation in PE is investigated by the pressure wave propagation method.The results show an obvious decrease in space charge accumulation in the fluorinated sample subject to a direct current high voltage with the increase of fluorination temperature,and there exists almost no charge accumulation in the sample fluorinated at 70℃.Attenuated total reflection infrared analyses indicate a substantial change in chemical composition of the sample surface layers by the fluorinations and an obvious increase in degree of fluorination with fluorination temperature increasing.Contact angle measurements and surface energy calculations indirectly indicate a significant increase in permittivity of the fluorinated layers by the fluorinations.Open-circuit thermally stimulated discharge current measurements further reveal different charge trapping properties of the fluorinated layers and the improved barrier properties of the fluorinated layer to the diffusion of the chemical species from the semi-conductive electrode to the PE with increase of fluorination temperature,thus indicating a corresponding decrease in free volume of the surface layer.The decrease in the free volume plays a more important role in suppressing the space charge accumulation,compared with the increase in permittivity and the change in charge trap.