Study On The Preparation And Properties Of Polymer-based Nanocomposites Reinforced By Graphene Oxide Materials

In recent years,with the rapid development of portable and wearable electronic devices to miniaturization,lightweight and multifunction,the integrated circuits with higher power density have been further promoted.In order to ensure the highly efficient operation of electronic products,the effective management of circuit heat becomes the key.Graphene materials has been widely used to improve the thermal properties of polymer composites for electronic packaging because of its excellent thermal and mechanical properties.However,the thermal properties of composites are still far from the expectation based on the excellent properties of graphene materials.In this paper,graphene oxide(GO)materials were used as the nanofillers for thermal reinforcement of epoxy resin matrix.The effect of GO materials on the curing reaction of the polymer matrix was studied.A method to further improve the thermal conductivity of GO/polymer composites was proposed.The mechanism of GO materials in improving the thermal conductivity and the thermal stability of the polymer matrix was analyzed.(1)A series of multi-layer graphene oxide(MGO,0.5,1,2,2.2,2.5,3wt%)/epoxy composites were prepared by in-situ curing method and the results showed that the thermal conductivity of 2wt%MGO composites reached a maximum,2.03 times that pure epoxy resin.The presence of 2wt%MGO percolating chains leads to an unprecedentedly sharp rise in energy barrier at final curing stage,but an increased epoxy curing degree is observed;however,this difference nearly disappears after aging or thermal annealing.These results suggest that the steep concentration gradient of-OH.originated from the 2 wt%MGO percolating chains,exerts the vital driving force on the residual isolated/trapped epoxy to conquer barrier for epoxy-MGO reaction.A modified Shrinking Core Model customized for the special layered-structure of MGO sheet was proposed to understand the resistance variation during the intercalative epoxy-MGO reaction.It shows that the promoted intercalative crosslinking is highly desirable for further improving the thermal conductivity of the composite,but it meets with increased resistance.Guided by the kinetic studies,targeted optimization on the cure processing strategy was accordingly proposed to promote the intercalative crosslinking,a thermal conductivity,2.96 times that of the epoxy,was got with only a small amount(30?)increase of the post-heating temperature.(2)A series of graphene oxide nanoplatelet(GONP)/epoxy composites were prepared by in-situ curing method,and the effects of morphology characteristic,surface functional groups contents,the exfoliation/dispersion state in the matrix,and the interfacial bonding strength of two kinds of GONP(r-GONP and f-GONP,similar in lateral size)on the thermal conductivity,Tg and its associated dimensional and structural stability of epoxy were investigated.The results showed that r-GONP(average thickness is 34nm)has a relatively rigid lamellar morphology with smooth surface;while the f-GONP(average thickness is 7nm)has a flexible gauzy morphology with winkled surface.Both r-/f-GONP were exfoliated and dispersed uniformly in the matrix(without 3wt%f-GONPs).The thermal conductivity of the composites under the same loading follows sequence:r-GONP/epoxy composites>f-GONP/epoxy composites>epoxy resin,while Tg follows a sequence:r-GNOP/epoxy composites>epoxy resin>f-GONP/epoxy composites.The stronger r-GONP/epoxy interfacial interaction formed was verified by "local" mechanical properties investigated using nanoindentation.The results of thermal expansion coefficient and thermogravimetric analysis showed that r-GONP/epoxy resin composites have higher thermal stability.Therefore,the thicker GONP endowed polymeric materials with higher overall thermal properties.