Study On Crystallization And Phase Separation Behaviors Of Miscible PBS/PVDF Blend Induced By Carbon Nanotubes And Its Resultant Properties

Polymer blending is an important way to develop polymer materials with excellent properties.As for the miscible blends,the microstructure is designed to realize the precise control of the macroscopic performance through tuning the miscibility and phase separation process of the components.Owing to the crystalline components for the crystalline/crystalline blend,more complex and interesting crystal structures can be achieved by regulating crystallization and phase separation,which have attracted more and more attentions from researchers.In recent years,many studies have found that the crystallization and phase separation behaviors of miscible blends are closely related to the shape,dimension,types of functional groups on the surface,content and other properties of the nanopariticles when adding nanoparticles into such blends.Carbon nanotubes(CNTs),as typical one-dimensional nanoparticles,have a large aspect ratio,specific surface area and a good affinity with the polymer matrix.Due to the different affinity between CNTs and the two components,on the one hand,the molecular chains of the component with stronger affinity were selectively adsorbed on the surface of CNTs,leading to the local concentration fluctuation;on the other hand,CNTs can induce crystallization of crystalline component and change the crystallization kinetics.Therefore,the introduction of CNTs has an important influence on the crystallization and phase separation mechanism.The purpose of this study was to explore the effect of CNTs on the crystallization and phase separation behavior of PBS/PVDF miscible blends and its resultant dielectric properties.The carboxyl functinanlized CNTs were introduced into the crystalline/crystalline PBS/PVDF miscible blend to prepare the ternary nanocomposites.Firstly,the effect of CNTs on the phase separation behavior of the blends was studied by dynamic rheological measurements.Then,the effects of CNTs on the nucleation efficiency,crystallization rate and crystalline morphology of PBS and PVDF components were studied systematically during the cooling process.Finally,based on the research of crystallization and phase separation behavior of PBS/PVDF blends induced by CNTs,the formation mechanism of hierarchical isolation structure formed by crystallization induced phase separation and its resultant dielectric properties of the nanocomposites were explored.The main results obtained in this work are listed as follows:(1)The PBS/PVDF/CNT nanocomposites were prepared by one-step melt blending process.It was found that the morphology of the matrix was homogeneous and homogeneous dispersion of CNTs in the nanocomposites was achieved.The calculation of interfacial tension shows that a small amount of PVDF and PBS molecular chains were adsorbed on the CNTs surface in the melt state.Among them,the molecular chain of PVDF is slightly more.In this case,CNTs act as entanglement junctions,which enhance the entanglement density and phase stability of the blend leading to the enhancement of the phase separation temperature.Therefore,the introduction of CNTs is helpful to improve the phase separation temperature of PBS/PVDF miscible blends and to slow down the phase separation process.(2)The PBS/PVDF/CNT nanocomposites were prepared by two-step melt blending process.The interfacial tension calculation showed that the affinity between CNTs and PBS was the strongest,followed by the affinity between PBS and PVDF molecular chain.The study of non-isothermal crystallization behavior showed that,on the one hand,the introduction of CNTs can induce the crystallization of PVDF and PBS at the same time,but the effect on the crystallization of PBS component is more significant.On the other hand,compared with PVDF/CNT and PBS/CNT binary composites,the nucleation ability of CNTs was restricted in the ternary nanocomposites,and the nucleation efficiency was significantly reduced.This is due to that PBS would like to peel off the adhesion of PVDF on CNTs resulting from the preferable adsorption of PBS on CNTs surfaces when PBS was blended with the PVDF/CNT masterbatch.The majority of CNTs surface was covered by the PBS due to the better interaction between PBS and CNTs,giving rise to improved crystallization of PBS on CNTs.The unremoved PVDF chain also crystallized on CNTs surface due to the heterogeneous nucleation effect.The study of isothermal crystallization behavior showed that the significantly increased nucleation density and the accelerated crystallization rate of PVDF and PBS components were obtained.Compared with PVDF/CNT and PBS/CNT binary composites,the restricted nucleation ability of CNTs in the ternary nanocomposites was further verified.In addition,the introduction of CNTs is conducive to the formation of the concentration fluctuations in the miscible blend,inducing the occurrence of microphase separation,which is related to the selective adsorption of CNTs.(3)Firstly,a series of PBS/PVDF/CNT nanocomposites with different compositions were prepared by regulating the contents of PBS.It was found that,compared with the PVDF/CNT binary composites,the introduction of the miscible PBS component was beneficial to improve the dispersion of CNTs and improve the dielectric properties of the nanocomposites in the non-isothermal crystallization process.Secondly,compared with non-isothermal crystallization,the dielectric properties of the composites were enhanced greatly after isothermal crystallization.Further analysis indicates that the CNTs were uniformly distributed in the matrix in the non-isothermal crystallization process,but for the isothermal crystallization process,the CNTs mainly distributes between interfibrillar and interspherulites of PVDF.The formation of hierarchical isolation structure is responsible for the enhancement of the dielectric properties of the composites.