多壁碳纳米管填充聚苯乙烯熔体的恒温依时性动态模量逾渗行为

TIME-DEPENDENT DYNAMIC MODULUS PERCOLATION OF MULTI-WALLED CARBON NANOTUBES FILLED POLYSTYRENE MELTS DURING ANNEALING

在恒温(170～190℃)热处理过程中,多壁碳纳米管(MWCNTs)填充聚苯乙烯(PS)熔体发生动态模量逾渗(DMP)行为,且该行为服从时-温叠加(TTS)原理.MWCNTs体积分数(φ)低于逾渗阈值(φc)时,填充熔体在恒温热处理过程中保持类液行为,热处理对MWCNTs分散状态无显著影响,动态储能模量(G')与动态损耗模量(G″)活化能(EG'与EG″)分别高于、低于PS黏流活化能(Eω),而与PS熔体恒频动态模量活化能相一致;φ>φc时,热处理促成MWCNTs进一步团聚,填充熔体在热处理过程中发生类液-类固转变,EG'与EG″均低于Eω,而动态逾渗时间活化能(Et'与Et″)显著高于Eω且随φ增高而增大.在逾渗转变区,EG'与EG″发生不连续变化.PS/MWCNTs复合体系的恒温依时DMP行为与MWCNTs聚集所导致的三维弹性网络的形成密切相关,PS大分子终端松弛不是决定DMP的关键因素.

A study on rheological behavior of multi-walled carbon nanotubes （MWCNTs） filled polystyrene （PS） melts submitted to isothermal annealing at temperatures from 170℃ to 190℃ was carried out.It is found that the filled PS melts with different volume fractions （φ） of MWCNTs from 0 to 0.05 underwent dynamic modulus percolation （DMP） during isothermal annealing and the DMP behaviors followed time-temperature superposition （TTS） principle disclosed for the first time.The filled melts with φ below percolation threshold exhibited liquid-like viscoelasticity during annealing,and the activation energies （EG＇ and EG″） of the dynamic storage modulus （G＇） and loss modulus （G″） were higher and lower than that of viscous flow （Eω） of pure PS melt,respectively,but were in agreement with the dynamic modulus activation energies of dynamic moduli of PS melt at the same frequency as that used in DMP test,the dynamic moduli were obtained through the dynamic frequency experiment.Annealing the melts having φ above percolation threshold caused MWCNTs to aggregate further so much as that the melts changed from the liquid-like to the solid-like.In this case,both EG＇ and EG″ were smaller than Eω while energies （Et＇ and Et″） of liquid-like to solid-like transition were significantly higher than Eω.Moreover,the activation energies of dynamic modulus exhibited a sharp decrease in the percolation transition region.It was suggested that the isothermal time-dependent DMP was closely related to the formation of the MWCNTs aggregation-induced construction of three-dimensional elastic network while the terminal relaxation of PS macromolecules was not the determinant factor for DMP.