聚氨酯涂膜弹性模量的AFM测定及微观结构分析

Determination of elastic modulus by atomic force microscopy and microstructure analysis for polyurethane coating film

为测定聚氨酯涂膜的弹性模量,建立了正三棱锥形态原子力显微镜(AFM)探针与涂膜的力学接触模型。同时,通过分析AFM的力学测试曲线,得出了探针与涂膜之间的力-压痕深度关系,并将其与力学接触模型相结合,确定了涂膜的弹性模量。此外,通过正电子湮灭技术测试了涂膜的微观结构,并与其弹性模量进行了对比分析。最后,采用灰色关联理论对微观结构参数与涂膜弹性模量的相关性进行了研究。结果表明:涂膜的弹性模量测定结果为6.118~6.917 MPa,与现有文献中聚氨酯涂膜弹性模量的研究结果一致,证明该方法测定结果准确。由于自由体积尺寸及含量的增大降低了基材对其分子链段运动的限制能力,故涂膜的弹性模量与其自由体积孔径及自由体积分数均呈负相关性,其中,涂膜的自由体积平均孔径对其弹性模量的影响程度更高。

In this work,the mechanical contact model between normal triangular atomic force microscopy(AFM) probe and coating film was established,which aims to measure the elastic modulus of polyurethane coating film.Whilst the force-indentation depth relationship between the probe and the coating film was obtained by analyzing the AFM′s mechanical test curve,and the elastic modulus of the coating film was determined by combining the newly established model.In addition,the microstructure of the coating film was tested using positron-annihilation technology,and compared with its elastic modulus.Finally,the grey correlation theory is used to analyze the correlation between the microstructure parameters and the elastic modulus of the coating film.The results show that the elastic modulus of the coating film was measured within the region of 6.118 MPa to 6.917 MPa.This is consistent with the research results of the elastic modulus of polyurethane coating in existing literature,which guarantees the validity and accuracy of the present method.The elastic modulus of the coating film is negatively correlated with its free volume aperture and free volume fraction since that the restriction ability of the substrate to its molecular chain segment movement is significantly lowered with the increase of free volume size and content.Among them,the free volume average pore diameter of the coating film has higher effects on its elastic modulus.