| Polycarbonate（PC）/polymethylmethacrylate（PMMA）blends have been widely used in the fields of electronic appliances,communication equipment and so on.However,with the development of 5G network,higher requirements are put forward for the thermal conductivity of PC/PMMA blends in these fields.Graphene（GNs）has excellent thermal conductivity,and is widely used as filler for preparing thermal conductive polymer blends.However,graphene is easy to agglomerate in polymer.Therefore,how to control the dispersion and distribution of GNs in polymer matrix to build a thermally conductive network structure,improve the interface interaction between GNs and polymer matrix and reduce the interfacial thermal resistance have become the key issues in preparing thermally conductive polymer blends with GNs as filler.In this paper,by designing different blending sequences,combining GNs surface design with kinetics,and regulating the selective dispersion and distribution of GNs in PC/PMMA blends and the phase morphology of composite materials,a heat conduction network structure was constructed in PC/PMMA blends.The effects of blending sequence,surface modifier structure and GNs content on the dispersion and distribution of GNs in PC/PMMA blends,material interface and properties of blends were studied.The mechanism model of phase morphology evolution and formation of thermal conductive network structure of blends was established,and the structure-activity relationship between structure and properties of thermal conductive polymer blends was clarified.The related research results have important theoretical significance and practical value for developing thermal conductive polymer blends with excellent comprehensive properties.The main research contents and results of this paper are as follows:1.Three different melt blending sequences(PC,PMMA,GNs blending（one-step method）;PC/GNs master batch blended with PMMA（two-step method）and PMMA/GNs master batch blended with PC（two-step method）were used to prepare blends.TEM characterization showed that GNs was mainly selectively distributed at the interface between PC and PMMA,and a small amount distributed in PC phase.The wetting coefficient（ωa）was calculated by young’s modulus formula,and theωa of the material was 0.06 and-0.35 at 25℃and 250℃,respectively,ranging from-1<ωa<1.GNs was predicted to be mainly distributed at the interface between PC and PMMA,which confirmed the TEM results.SEM results show that the dispersed phase size of PMMA composite prepared by one-step method is the smallest.Combined with SEM,TEM and rheological test results,the phase morphology evolution mechanism model of composite prepared by one-step method was established.For the three different preparation methods,PC/PMMA/GNs blend prepared by one-step method not only have good thermal and electrical conductivity,but also have good strength and toughness under the condition of adding 0.05 wt%GNs.2.GNs was modified with supercritical carbon dioxide as medium and KH550,KH560,KH570 and Tannin as modifiers.TEM results show that compared with unmodified GNs,modified GNs is still mainly distributed at the interface between PC and PMMA,and a few are distributed in PC phase.GNs surface energy is 50.11 m J·m-2,and that of KH550,KH560,KH570 and Tannin modified GNs is 67.78 m J·m-2,43.49m J·m-2,24.05 m J·m-2,50.67 m J·m-2 respectively.KH560 and KH570 reduce GNs surface energy and improve GNs dispersion.The interfacial energy between GNS modified by KH560 and PC is 0.17 m J·m-2,which is much smaller than that between other fillers and PC.Therefore,GNs-KH560 has the best dispersion in polymer matrix,and a more effective heat conduction network is constructed.Compared with PC/PMMA,the thermal conductivity,electrical conductivity and mechanical properties of PC/PMMA/GNs-KH560 blend with GNS-KH560 are improved by 11.17%,21.63%,0.05 wt%and 46.11%,respectively.3.The effect of GNs-KH560 content on the structure and properties of PC/PMMA（70/30）blends was studied.TEM results show that with the increase of GNs-KH560content,most of GNs-KH560 is still mainly distributed at the interface between PC and PMMA,and a small part is distributed in PC phase,and no obvious aggregation phenomenon is found.With the increase of GNs-KH560 content,the particle size of PMMA in the dispersed phase of the composite tends to decrease gradually.When the content of GNs-KH560 reaches 0.30 wt%,the phase morphology of the blend changes from sea-island structure to partially co-continuous structure,and GNs-KH560 is distributed on the interface of partially co-continuous structure to form a more perfect heat conduction network,which obviously improves the thermal conductivity,electrical conductivity and mechanical properties of the blend. |
