Preparation Of Organic-Inorganic Hybrid Nanoparticles By Radiation Induced Grafting And The Investigations On The Polymer Nanocomposites

Polymer nanocomposites（PNCs）have been defined as“a type of material which contain one or more nanoparticle（NP）components within a polymer matrix”.Desirable or synergistic physicochemical properties can be achieved in PNCs,which is hardly obtained in their individual components alone.However,most nanoparticles are thermodynamically immiscible with polymer due to the combination of low mixing entropy.Therefore,significant aggregation is often occurred during simple mixing procedure.The surface modification of organic components on nanoparticles,which prepared by traditional chemical reactions,is an effective strategy to improve the compatibility between NP and polymer matrix.However,modification is restricted since it requires complementary reactive groups in reactive polymers and nanoparticles,respectively.On the other hand,the formation of single-phase nanocomposites by self-assembly is too hard to achieve due to the limited content of organic modification.Nowadays,the hybrid nanoparticles was commonly applied as fillers for PNCs.Therefore,it is necessary to develop a more simple strategy for the surface modification of nanoparticles with high content and high molecular weight organic components.Recently,radiation-induced grafting methods（RIG）have been found to be one of the most versatile means for the preparation of nanohybrid.It makes possible to introduce a range of functional groups or polymer onto nanoparticles surface abundantly available in various physical forms.In this work,we proposed a new strategy to surface modify the nanoparticles based on the“radiation grafting”process.The feasibility of surface modification strategy was verified by changing the core of hybrid nanoparticles.In addition,the hybrid nanoparticles was then blended with polymer matrix.The dispersion of nanoparticles with different surface modifications in the polymer matrix,the structure and properties of polymer nanocomposite was studied systematically.Finally,the hybrid nanoparticles was melting-processed to prepare functional single-phase nanocomposites directly.Therefore,it developed a more simply strategy for the preparation of nanocomposites.The detailed research in this dissertation were listed as follows:（1）Preparation of PVDF grafted SiO₂by radiationThe hybrid nanoparticles of PVDF grafted SiO₂（F-SiO₂）were prepared via“radiation grafting”process.The chemical structure,thermal stability and crystallization properties of F-SiO₂ was studied systematically.The PVDF was grafted onto the SiO₂ surface successfully.The increasing of PVDF feed ratio and the absorption dose of grafting reaction can significantly improves the reaction opportunities between SiO₂ and PVDF,leading to the increased of grafting degree of PVDF on the nanoparticles surface.（2）Structure and property of SiO₂/PVDF blendsThe blends of PVDF and SiO₂ with different surface modifications were prepared by melt processing.The dispersion of modified SiO₂ in PVDF matrix was studied systematically.It was found that only F-SiO₂ can be dispersed in PVDF matrix uniformly to improve the mechanical properties of the blends,as compared with pristine silica since the PVDF chain on the silica surface improved the compatibility between nanoparticles and matrix.（3）Preparation and property of PVDF grafted BTBarium Titanate nanoparticles（BT）were synthesized by“hydrothermal synthesis”method and its size was about 70 nm.Compared with the preparation of F-SiO₂,the strategy of PVDF grafted BT（F-BT）surface modification was similar.It was also synthesized by a“radiation grafting”method.It was indicated that the grafting degree of PVDF on BT surface can be controlled by adjusting the vinyl group content,PVDF feed ratio and the absorption dose of grafting reaction.The PVDF on the BT surface was mainlyβ-crystalline.（4）Structure and property of BT/PVDF blendsThe blends of PVDF and BT with different surface modifications were prepared by melt processing.It was similar to the SiO₂/PVDF that only F-BT can be dispersed in PVDF matrix uniformly and improved the mechanical properties of the blends.Increasing the PVDF grafting content on F-BT surface can also improve the dispersion of nanoparticles in PVDF matrix significantly.More importantly,with the enhancement of BT dispersion and filling content in PVDF matrix,the dielectric properties of the BT/PVDF blends was also improved.（5）Preparation of flexible F-BT dielectric materials with high dielectric constantThe F-BT hybrid nanoparticles with different surface PVDF grafted content were used to prepare the flexible dielectric films with high dielectric constant.Result showed that the F-BT could not to be melt-processed when the grafting content of PVDF on the F-BT surface was low（5wt%）.However,with the increasing of the PVDF grafting ratio,the processibility and mechanical performance of the F-BT dielectric materials was improved.It can be contributed to the dense network between nanoparticles surface,which formed by the surface grafted-PVDF chain entanglement.This work provides a new strategy for the preparation of novel flexible dielectric materials with high dielectric constant.