Molecular Simulation Study On The Curing Behavior Of Epoxy/Amine System And Structure Design Of Novel Carbon-based Hybrid Reinforcement Materials

Highly cross-linked epoxy/amine curing systems are widely used as resin matrices,especially for carbon fiber reinforced polymer composites due to their excellent mechanical properties,heat resistance and adhesive performance.It is generally known that the physical and chemical properties of polymers can be tailored by varying the composition of the constituent epoxy resin and the curing agents,controlling the curing process or conditions as well as adding secondary phase fillers.Through adjustment of the network architecture,the epoxy/amine system provides an attractive characteristic which can satisfy the performance requirements of the resin matrix for polymer composites.Therefore,it is a common agreement that desirable performance must surely arise from an adequate understanding of the structure-property relationship of the epoxy matrix,thereby serving as guidance to design high-performance polymer matrices for advanced composites.So far,the mechanical strength and toughness of existing epoxy/amine systems are still not enough for practical applications.Driven by the pursuit of more and higher performance requirements,such as multifunctional properties,improved dispersion and interfacial interaction of engineering nanocomposites,hybrid nano-materials and three-dimensional(3D)graphene aerogel materials gradually comes into the view of material researchers.Accordingly,our research work is shown as followed:(1)The curing kinetics and thermo-mechanical characteristics of two kinds of high-performance amine cured tri-functional epoxy resin compounds,including diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate(TDE-85)and N,N-diglycidyl-4-glycidyloxyaniline(AFG-90),were systematically studied.Different to the simple bi-functional epoxy resin studied before,the increase in epoxy functionality and resultant asymmetric monomer structure made the whole curing behavior more difficult to analyze.In this paper,a methodology,which combined atomistic molecular simulation with experimental research,was established to expound the effect of the asymmetric epoxy monomer structure on the reaction kinetics and ultimate performance of tri-functional epoxy/amine system.(2)Autocatalysis reaction models were proved to be suitable for both curing systems according to the non-isothermal DSC analysis.Molecular simulation,including DFT and MD methods,were used to analyze the difference in reaction activity of two epoxy systems(TDE-85/DDS and AFG-90/DDS).According to the simulation details,the local chemical structure had little effect on the absolute charge values of specific epoxy groups,but directly influenced their bond order value.In addition,the relative rigid molecular chain segment also strongly affected the cross-linking procedure.(3)Once the network building reaction was complete,the epoxy/amine systems turned into highly cross-linked three-dimension viscoelastic structure.The effect of the epoxy monomer structure on the eventual thermo-mechanical properties can be attributed to the discrepancy in physical topological structure and the chemical interaction.The packing mode and the average molecular weight between cross-links strongly reflected the network structure,which is associated closely with the free volume,and dominated the motion ability of the polymer segment.Simultaneously,the chemical groups in epoxy monomer affected cohesive energy density of the epoxy matrix,which determined the intermolecular interactions.These comprehensive factors led to the difference in the thermo-mechanical characteristics between two epoxy systems(TDE-85/DDS and AFG-90/DDS).(4)A novel 3D nanomaterial(MWCNT-PDA-POSS)with bump structure was prepared by combining multi-walled carbon nanotubes(MWCNTs)and polyhedral oligomeric silsesquioxanes(POSS)via mussel-inspired chemistry.A two-step process was used for preparation of MWCNT-PDA-POSS,and the potential chemical reaction between carboxyl-functionalized MWCNT(MWCNT-COOH),polydopamine(PDA)and amino-functionalized POSS(POSS-NH2)was investigated.Furthermore,the unique bump structure of the MWCNT-PDA-POSS was observed.As nanofillers in the resin matrix,the bump structure can provide higher specific surface area while some unreacted catechol functional groups of PDA would participate in the cross-linking reaction of epoxy resin,leading to the interface strengthening between the MWCNTs and resin matrix.Therefore,the MWCNT-PDA-POSS resulted in an enhancement of 20.6%in compressive strength and 33.3%in the compressive modulus compared to the neat epoxy,which exhibited potential application in the multi-scale reinforced composites.(5)A facile synthesis of 3D ultra-light(?2.52 mg/cm3)graphene-polydopamine modified carbon nanotube composite aerogels(GCPCA)that needed no additional reducing agents during the forming process was reported.The composite aerogels exhibited highly repeatable compressibility and superior electrical conductivity.The "flexible" PDA layer on the surface of MWCNTs played a role as dispersant to uniformly disperse MWCNTs into original graphene system and temporarily acted as cross-linking and reducing agent during the self-assembled process.Then the PDA was removed by annealing process at 750 ?,which not only enhanced the electric conductivity but also reduced the density of the resulting GCPCA.The obtained GCPCA was highly compressible and exhibited outstanding fatigue resistance under static and dynamic compression testing.The unique synthetic method and performance advantage of the aerogels will be of great value in a variety of applications such as epoxy composites,oil adsorption,and pressure sensor.