太赫兹光谱技术应用于聚烯烃薄膜孔隙率检测

Application of Terahertz Spectroscopy in Porosity Detection of Polyolefin Films

聚烯烃薄膜材料的孔隙率会影响材料的力学性能、绝缘性和贯通性,但少有对聚烯烃孔隙率无损检测的精确方法。本文以有效介电常数为桥梁,建立了四种材料等效折射率与孔隙率之间的等效模型;通过实际测试电池隔膜及微孔滤膜的太赫兹时域光谱,定量得到材料的折射率、介电常数、孔隙率等数据。结果表明:对于聚烯烃材料与空气的两相介质,其孔隙率与介电常数存在高相关性;采用改进的有效介质模型测得的孔隙率与常规的气体置换法测得的孔隙率的平均相对误差在2.53%左右;利用太赫兹光谱测量聚烯烃薄膜的孔隙率具备一定的可行性,有望成为薄膜检测的补充手段。

Although the polyolefin film porosity is known to affect the material’s mechanical properties,insulation,and penetration,few accurate methods are available for its nondestructive detection.In this study,the effective permittivity is used as a bridge for establishing four equivalent models between the equivalent refractive index and porosity of materials.By practically testing the terahertz timedomain spectrum of the battery separator and microporous filter membrane,the refractive index,permittivity,porosity,and other material properties are quantitatively obtained.The results show that for a biphasic medium comprising the polyolefin material and air,the porosity and permittivity are highly correlated.The average relative error is approximately 2.53%between the porosities measured using the improved effective medium model and conventional gas displacement method;therefore,terahertzspectroscopybased porosity measurements are feasible for polyolefin films and should become a supplementary filmdetection method.