Study The Relationship Between Microstructure And Nanomechanical Properties Of Materials By Nanoindentation Technology

Atomic force microscope(AFM)is a powerful tool for surface analysis at the nanometer or even atomic resolution.It can not only characterize the topological structure and local physical properties of materials,but also manipulate samples at the nanoscale.Peak Force Quantitative Nanomechanical Mapping(PF-QNM)based on AFM has attracted more and more attention due to its nondestructive characterization,high resolution imaging and parallel quantitative performance mapping.In this paper,microstructure and nano-mechanical properties of thermoplastic elastomer(TPE)and supramolecular assemblies were characterized and analyzed by the PF-QNM technology based on AFM.It would greatly help to establish the relationship between the structure and mechanical properties of materials.The methodology for material characterization was further developed and improved by the PF-QNM technology.The main contents are as follows:1.The microstructure and nano-mechanical properties of nitrile rubber/polyvinyl chloride(NBR/PVC)composites were first studied by the PF-QNM technology.First,NBR/PVC composites were prepared by mechanically mixing NBR containing 28%acrylonitrile with plasticized PVC.Then the microstructure,homogeneity and nano-mechanical properties of NBR/PVC composites were characterized by the PF-QNM technology.Beyond measuring and discriminating structure and nano-mechanical properties of each phase,we tuned the AFM tips and the peak force parameters in order to reliably image samples.Research shows that a three-phase coexistence of an unmixed NBR phase,the mixed phase,and PVC microcrystallites is directly visualized in NBR/PVC composites by the PF-QNM technology.And the structure and Young's modulus of each phase were directly provided.This study helps us to further understand the structure-mechanical property relationship of thermoplastic elastomers.2.The structure and mechanical properties of C6-4ClPBI and C12-4ClPBI with different alkyl chain lengths on one of N positions have been systematically studied by the PF-QNM technology.In order to improve the solubility and self-assembly performance of 4ClPBI,Oligo(ethylene glycol)was introduced on one of N positions.The other N position was attached to different alkyl chain lengths.Using methanol/tetrahydrofuran(MeOH/THF)mixed solvent,the structure and mechanical properties of C6-4ClPBI and C12-4ClPBI assemblies formed under different solvent polarity were studied by the PF-QNM technology.Studies show that the length of the alkyl chain has a great influence on the process of supramolecular self-assembly and the microstructure of assemblies.Under the condition of high solvent polarity(C_M=80 v%),Young's modulus of C6-4ClPBI assemblies with micron-sized blocked cuboid structure was as high as 3.1 GPa.However,Young's modulus of C12-4ClPBI assemblies with nanoscale rod structure was only about 2.5 GPa.When the alkyl chain is long,the assemblies formed by the non-planar 4ClPBI has poor regularity,relatively small size and low Young's modulus.The relationship between the structure and mechanical properties of supramolecular self-assembly was established.