Molecular Dynamics Study On The Mechanical Properties Of Modified Nanopaticle Reinforced Polymer Matrix Composites

At present, nanoparticle reinforced polymer matrix composite is one of the researchemphasis in the field of nanometer materials science. With the excellent properties ofnanoparticles and polymer, it is widely applied in many fields. Because nanoparticles have manysurface atoms, highly active and with many broken keys, easily agglomerated, the nano sizeeffect cannot act effectively. The experimental results of many researchers show that thenanoparticle surface treatment can effectively improve the properties of composite. With thedevelopment of computer technology, molecular simulation software as a supplement of theexperiment can predict the influence factor in qualitative and quantitative analysis, providingmore intuitive results for analysis and further guide for experiments.Effective moduli of fiber-reinforced polymer matrix composites filled with nanoparticleconsidering the effect of linear change of interphase are presented in this paper based on theMori-Tanaka method. The formula to calculate the elastic modulus and Poisson’s ratio arederived and effects of the thickness of interfacial layer, the particle size and the volume fractionof nanoparticles on the effective elastic moduli of the composites are also discussed.According to the molecular dynamics theory, the molecular model of SiO2and polyimide(PI) can be built by the Materials Studio software and make the following analysis:1. SiO2/PI composite model is established, the mechanical properties are calculated, andthe Young’s modulus and Poisson’s ratio of the unit cell are obtained，effects of theparticle size and the volume fraction on the mechanical properties of the composites arediscussed. The results show that nanoparticle can improve the mechanical properties ofcomposites in some extent compared with pure polyimide.2. In the Materials Studio software, the SiO2nanoparticles are treated in three ways: siliconproply modified, directly and covalently grafted with the polyimide, and the mechanicalproperties of three kinds of modified nanosilica polyimide composites are calculated,effects of the particle size and the grafted ratio on the mechanical properties of thecomposites are discussed. The energy variation of grafted and ungrafted nanosilica is analyzed from an energetic standpoint, predicting the force that plays a major rolebetween the particle and matrix interface, revealing the effect mechanism of themodified nanoparticles on the mechanical properties of the composites. The resultsshow that the Young’s modulus of composites increases by15%when the grafting ratiois5%.3. The interaction between nanoparticles is simulated and calculated, influence factorswith the leading role for reunion are analyzed.