The Preparation And Investigation Of Molecular Dynamics Simulation Of AO-70/NBR Composites

Polymer damping materials can convert mechanical or sound energy into heat energy and then dissipated through its unique viscoelasticity,in recent years,in the preparation of high performance damping composite material,adding small organic polarity molecule to the polymer has arouse the interest and attention among scholars.The key for the small organic polarity molecules to improve the damping performance of rubber is the reversible hydrogen bonds formed between hybrids.Under the outside vibration,the hydrogen bond will fracture and in this process,mechanical energy turns into chemical energy,and then form a new hydrogen bond,in which chemical energy turns into heat energy and dissipate out,thus cause a high damping effect.In this paper,the author has adopted the whole-atom/molecular dynamics simulation from the molecular level to do the study of AO-70/NBR composite material micro structure and damping performance improvement mechanism.The author predicts the types and amount of possible hydrogen bond forming in this system,and uses some experimental means such as infrared spectrum analysis,thermal properties and dynamic mechanical analysis to verify the simulation's accuracy in a reverse way.(1)In the first part of this paper(in the third chapter),the author analyzes the polar atomic electronegativity of hindered phenol small molecule AO-70/NBR composites through the atomistic molecular dynamics simulation and predict that there are Type A,B,C,D four hydrogen bonds in the system,namely,Type A(AO-70)-OH…NC-(NBR),Type B(AO-70)-OH…O=C-(AO-70),Type C(AO-70)-OH…OH-(AO-70),Type D(AO-70)-OH…O-C-(AO-70).The radial distribution function reveals that Type A has the highest probability and the AO-70/NBR composites with AO-70 content of 66 or 109 phr had Type C and D.Then the author calculates the solubility parameters of AO-70 and NBR(the acrylonitrile mass fraction of 41%),the results prove that there is a good compatibility between AO-70 and NBR.Meanwhile,the AO-70/NBR composite with AO-70 content of 109 phr has the smallest fractional free volume,largest number of H-bonds,highest binding energy and cohesion energy density,demonstrating that the highest energy needed to destroy the hydrogen bonds and thus the author can predict AO-70/NBR(109/100)composite has the best damping performance.(2)In the second part of this paper(in the fourth chapter),according to the design of molecular simulation component ratio,AO-70 is added to the NBR in the mass ratios of 0/100,22/100,44/100,66/100,88/100 and 109/100 respectively.The author analyzes the dispersion of AO-70 in NBR matrix,discovering that there were amorphous and crystalline state of AO-70 in NBR matrix through scanning electron microscope.Fourier transform infrared spectrum and Nuclear magnetic resonance hydrogen's results discover that there is a strong hydrogen bonding interaction in AO-70/NBR composites,what's more,the hydrogen bonding is gradually enhanced with the increase of AO-70 content.Temperature-dependent FTIR shows that Type A is the most stable.Differential scanning calorimetry and dynamic mechanical analysis datas show that the glass transition temperature of AO-70/NBR composites increases with increasing of AO-70 content on the reason that the H-bonds which hinder the movements of molecular chains.The damping property of AO-70/NBR composites get a noteworthy increase with the introduction of AO-70—max tan ? increases by 66.9%.Thus,the author confirms the AO-70/NBR(109/100)composite has the best damping performance from the aspect of experiment,which consistents with the simulation results.