聚甲基丙烯酸甲酯材料(PMMA)纳米压/划痕变形热恢复的实验研究

Experimental study on thermal recovery of nano-indentation/scratch deformation of poly(methylmethacrylate)

聚甲基丙烯酸甲酯(PMMA)是常见的光伏电池封装材料。本文采用锥形和球形两种压头,利用纳米压痕仪开展了PMMA的纳米压痕和划痕实验。基于表面形貌扫描得到的PMMA材料在不同温度热处理后压痕与划痕变形随时间恢复的演化规律,分析了时间、温度和压头形状等对PMMA材料压/划痕变形恢复过程的影响机理。结果表明,压/划痕变形恢复速率随着时间的增加显著减小,而变形恢复程度在热处理温度越接近玻璃化转变温度时越大。球形压头产生的压/划痕变形均匀,变形恢复能力明显高于Berkovich三棱锥压头。通过块体材料宏观拉伸蠕变恢复实验,基于时温等效原理对长时变形恢复情况进行评估。发现在黏弹性范围内,宏观实验结果可用于PMMA材料纳米压痕变形长期恢复的预测;而纳米划痕由于其特殊的加载变形方式,为避免估计变形恢复量时产生误差,需要对宏观实验所得参数加以修正。研究结果可对光伏电池封装材料的设计和耐划伤长期性能评估提供建议。

Polymethylmethacrylate(PMMA)is a commonly used photovoltaic cell packaging material.Nano-indentation and nano-scratch experiments of PMMA were carried out with both Berkovich and spherical indenters.The characteristics of deformation recovery under different heat treatment temperatures were studied.The evolution of residual indentation and scratch deformation with time was investigated.The results indicate that the recovery rate of indentation/scratch deformation decreases significantly with time,and the extent of deformation recovery becomes larger when the heat treatment temperature is closer to the glass transition temperature.Because of the symmetrically and uniformly distributed deformation of spherical indenter,its recovery capability is much better than that of Berkovich indenter.While the long term recovery of nano-indentation can be predicted with the help from the data of macroscopic tensile creep recovery test of bulk material based on time-temperature equivalent principle,the long term recovery of nano-scratch deformation cannot be obtained directly.These findings give meaningful insights for the design and long term scratch resistance evaluation of the packaging material for photovoltaic applications.