Molecular Dynamics Simulation Study On Micromechanisim About Effect Of Reinforcing Agent And Plasticizer On Mechanical Properties Of Rubber Nanocomposites

Rubber nanocomposite,one kind of strategic resource,has been widely used in national economy,national defense and military industry.The performance of nanocomposite highly depends on the dispersion state of fillers and other compounding ingredients and the interaction between rubber matrix and them.During the past several decades,through experimental techniques and computational approaches,researchers have been paying much attention to the reinforcement mechanism the fillers and compounding ingredients have on mechanical properties of rubbers.In the system of rubber nanocomposite,there exists multilevel and multiscale interaction.That is,whether chemical group interaction in molecular scale and dispersion of fillers in nanoscale,or self-assembly structure in submicroscopic scale,will all significantly affect the macroscopic mechanical,thermal and electrical performance of rubbers.However,traditional methods can barely characterize the micro structure deeply and thoroughly.As a novel and increasingly developing methodology,molecular dynamic(MD)simulation will play more and more pivotal role in exploring the molecular microscopic mechanism of mechanical reinforcement in nanocomposites field.Based on the above research background,by adopting united-atom and atomistic molecular dynamic simulation,our work focuses on the study of microscopic mechanisim reinforcing agent and plasticizer have on the mechanical properties of rubber nanocomposites.The following two aspects is where we mainly carry out from:Micromechanism study of the effect of graphene(GP)packing on mechanical performance of rubber nanocomposites:Through united-atom molecular dynamics simulations,we build a series of GP reinforced cis-1,4-polybutadiene(cis-PB)models with two novel GP structures,intercalated and stacked GP structures,to investigate the effect of different GP packing patterns on the chain structure,chain dynamics,uniaxial tension and visco-elastic behaviors,and correlate the microscopic mechanism with macroscopic mechanical properties.Simulation results show that the interlayer polymer chains in the void of intercalated GPs are strongly confined,leading to higher bond orientation of polymer chains during the stretch process compared with monodisperse systems.And due to this restriction effect,intercalated systems exhibit higher tensile stress under large tensile strain.For stacked systems,the interaction within GP layers and the orientation of the whole stacked GP structure play dominant roles in mechanical and visco-elastic properties.Furthermore,from the results that stacked systems have higher tensile stress and intercalated systems exhibit a higher storage modulus,we can conclude that GP-GP interaction makes greater contribution than GP-PB interaction and the chain confinement effect to the tensile behavior,whereas the restriction and orientation of polymer chains become more crucial factors than the GP-GP interaction under shear conditions.Micromechanism study of the effect of C5/C9 petroleum resin composition on mechanical performance of rubber nanocomposites:It is well known that C5 and C9 petroleum resins have been widely used in the rubber industry as they can soften,tackify and reinforce the rubber matrix and improve their processing ability as well.And these effects depend highly on the compatibility and interaction between rubber matrix and resin additive.Herein,we choose five commercially used petroleum resins(two kinds of Coumarone resins,poly(a-methyl styrene-co-styrene)resin,C5/C9 copolymerized petroleum resin,and 5#-C9 petroleum resin)and two industrial solution polymerized styrene-butadiene rubbers(SSBR)to find the most suitable resin composition for one specific rubber,as well as figure out the dominant mechanism that affects rubber micro mechanical properties.By employing atomistic MD simulation,firstly,we study the influence of resin composition on the compatibility between them.Through the experimental testing of solubility parameter(8)and the simulative calculation of ?,the corresponding R value,binding energy(Ebinding),self-diffusion coefficient(Ds)and free volume fraction(FFV),we find that:(1)the compatibility order of experiment is in consistent with the simulation result;(2)because of the similar molecular structure of five resins,compatibility trends obtained by different simulation approaches generally fits,but differ in detail;(3)the compatibility between SSBR and resins do not dominates the mechanical performance of this particular hybrid system.We then further study the influence of resin composition on the interaction between them.By building the models of resin chain/SSBR unit system and resin unit/SSBR unit system,calculating the interaction energy and comparing these results with experimental micro modulus distribution curves,results show that:(1)styrene unit has the strongest interaction with resins,while cis-1,4 unit has the weakest interaction;(2)resins have better compatibility with SSBR than cis-polybutadiene rubber,the chain/unit level interaction result is in line with the chain/chain level compatibility result;(3)the interaction intensity difference between styrene unit and cis-1,4 unit with resins is the most crucial role that affects mechanical properties.