Study On Mechanical Properties Of Gold Nanosphere-polymer Matrix Interface

Over the last decade,flexible conductive nanocomposites have attracted cosiderable attention due to their high elasticity and high conductivity,and have played an indispensable role in the development of flexible and extensible electronic and optoelectronic devices.The fabrication of flexible conductive composites with metal rubber as a typical example will greatly promote the development of 21 st century high technology including stretchable displays,soft biosensors,flexible energy storage devices,and smart textiles.In contrast to the continuous interface of conventional composites,the small scale effect of the nano-fillers in the nanocomposites enhances the effect of the van der Waals interaction between the nanoscale fillers and the matrix,forming a unique "nanofiller-matrix" interface.In addition to the nanofillers and matrix,this interface can be considered as the "third phase" in the nanocomposite,which would exert a substantial influence on the mechanical behavior and properties of the nanocomposite at different length scale.Therefore,it is thus essential to bring in an in-depth understanding of the constitutive relations,and quantify the mechanical properties of this nanoscale “filler-matrix”interface as the third phase in the nanocompsite.In spite of this,detailed study of such a nanoscale interface has not yet been reported in the literature for the novel metal rubber.This situation thus necessitates an immediate and comprehensive study of the mechanics of the “nanofiller-matrix” interface,which could be challenging due to its high anisotropy and nonlinearity.Motivated by this idea,this thesis aims to resolve the issues based on a multi-scale modelling techniques.On the one hand,continuum mechanics theories and Monte Carlo method are employed to study the mechanical behavior and properties of the "nanofiller-matrix" interface.Two different systems are considered.i.e.,single gold nanoparticle+polyethylene matrix and many gold nanoparticles+matrix composite;On the other hand,molecular dynamics simulations are performed to examine the effects of nanoscale interface and environmental factors on the overall properties of nanocomposites.This work has been done by comparingthe "pure polyethylene" and "gold nanoparticle-polyethylene" systems.The major outcomes of the present research are as follows:(1)Based on the Lennard-Jones potential,the analytic formulae have been derived for the first time in the literature for the cohesive energy and cohesive stress of the interface between the nanoparticle and surrounding matrix.(2)These analytical formulae show that the cohesive energy(per unit area)and cohesive strength of the interface increase with the increase of the radius of the golden particle.At a smaller radius,the curvature effect is very strong.It however gradually diminishes with the increase of the radius,and becomes negligible when the radius is sufficiently large.(3)Previous studies have been based on dilute solution assumptions,regardless of the interaction between gold nanoparticles.In this paper,the influence of the gold particle in the surrounding nanocomposites on the interface is investigated for the first time,and the applicable range of the dilute solution is suggested.(4)Finally,using the molecular dynamics simulation,the effects of radius and volume fraction of gold nanoparticle,temperature and strain rate on the mechanical properties(Young's modulus,Yield stress/strain,Fracture stress/strain)of the material were studied.It is shown that the "gold nanoparticle-polyethylene" system is different from the "pure polyethylene" system.