Investigation Of Segmental Relaxation Mechanism In Polymer Composites By Mechanical Spectroscopy

Polymer material is one of the indispensable materials in modern world and industrial production.In order to meet more performance requirements,in addition to researching and developing new type of polymers,polymer composites have become one of the research hotspots of polymer materials due to their excellent physical and chemical properties.At the same time,the performance improvement of polymer composites is closely related to the interaction between polymer matrix and second phase(nanoparticles or polymers),so the movement and dynamic relaxation behavior of molecular chains in polymer composites have been attracted much attention.However,most of the current studies focuce on the ? relaxation behavior near the glass transition temperature(Tg).But the mechanisms underlying ?'relaxation related to the longer-scale segmental movement above Tg are poorly understand.In this work,the typical polymer composites with different interaction were prepared.The molecular interaction between different components and the segmental relaxation dynamics were investigated by various techniques,such as liquid mechanical spectroscopy,differential scanning calorimentry,Fourier transform infrared spectroscopy,which has great significance to the the design,performance tuning and processing technology of polymer composites.Firstly,we prepared amorphous poly(methyl methacrylate)(PMMA)and semicrystalline poly(vinylidene fluoride)blends with different components,and studied the segmental relaxation dynamics of the blend.Meanwhile,the evolution of PVDF crystalline phase and the entanglement state of polymer chains with composition and temperature were analyzed.The results show that the interaction between PMMA and PVDF is strongly dependent on the composition.For the intermediate component(?PVDF=40%and 50%),the interaction between PMMA and PVDF is week due to the formation of PVDF intermediate phase and crystalline phase,which results in the acceleration of segmental relaxation and the decrease of relaxation time.However,if the PVDF crystalline phase is thinner,it will melt gradually with the increase of temperature.At this time,PMMA chains can penetrate into this region and entangle with PVDF chains,resulting in ?' relaxation slowing down and relaxation time increaseSecondly,we prepared PMMA/SiO2 nanocomposites and studied the effect of nanoparticles on the segmental relaxation dynamics of polymer.It was found that the interaction between unmodified nanoparticles and PMMA is weak,and the nanoparticles tend to self-agglomerate when ?SiO2>0.5%,which results in the local heterogeneity of polymer chains distribution.The mechanical spectroscopy results show that the motion unit concentration involved in ? relaxtion increases,but the ?'relaxation related to longer-scale segmental movements is hindered.When the content of nanoparticles is up to 0.7%,PMMA chains gather around the nanoparticles to form an interfacial layer due to the physical adsorption effect,leading to the decrease of the motion unit concentration involved in ? relaxtion and the slowing down of relaxation.However,due to the dissociation of the bounds between PMMA and SiO2 and the concentration heterogrnrity of polymer chains,the motion unit concentration involved in ?' relaxtion increased abnormally.Finally,in order to obtained polymer nanocomposites with good dispersion,the surface of SiO2 nanoparticles was modified.It was found that the modified nanoparticles have a stronger interaction with polymer chains and can be evenly dispersed in the polymer matrix.With the increase of SiO2 content,both of the local segmental ? relaxation and longer-scale ?' relaxation shift to higher temperature,and the concentration of relaxation units involved in movements decreases,the relaxations slow down.