Preparation Of Highly Conductive Composites Through Polyphenol Surface Modification Of Micro-nanoparticles

With the widespread use of electrical and electronic devices in industrial,commercial,and military fields,electromagnetic interference(EMI)has become a serious problem in recent years.Electromagnetic shielding rubber combines electromagnetic sealing and environmental sealing ability,high shielding effectiveness,strong environmental adaptability,low density,and low cost.It is widely used in the fields of aerospace,electronic communications,national defense and military affairs.Metal-coated electroconductive powder,with low cost,low density,good conductivity,is the most commonly used electromagnetic shielding filler.However,the domestic research in this area is relatively backward,and the production of metal-coated powder can't meet the needs of the military and civilian markets.Mussle-inspired dopamine modification has advantages of simple ingredients and equipment,mild reaction condition,environment-friendly,and applicability to various types of materials.It is a simple and effective surface modification method,which can effectively improve the binding force between the silver particles and the substrate.We have prepared highly conductive silver-coated powder through dopamine modification.Nevertheless,the high cost of dopamine and long reaction time limit its industrial production and application.The excellent adhesion of dopamine comes from the ortho-phenolic hydroxyl and amino groups in its structure.Therefore,we chose two low-cost catechol and polyamine instead of dopamine to reduce the production cost.The addition of an oxidant can promotes the oxidation of catechol to o-benzoquinone,and accelerates the deposition of poly(catechol-polyamine).In addition,tannic acid(TA),a kind of polyphenol extracted from plants,is rich in catechol and pyrogallol groups.TA can be quickly chelated with metal ions to deposit stable polyphenol-metal film on the surface of substrate,which is an efficient,environmental friendly surface modification method.In this paper,two kinds of polyphenol surface modification methods were studied to modify a variety of substrates and prepare highly conductive silver-plated powder.The details are as follows:(1)Silica microspheres were modified by oxidative co-deposition of catechol and polyamine.The optimum conditions for the deposition of poly(catechol/polyamine)(PCPA)were determined as follows:catechol and tetraethylenepentamine with a molar ratio of 3:1,the reaction pH of 9,and the reaction time of 4 h.The Ag+ can be absorbed by catechol group of PCPA through chelation of ortho phenolic hydroxyl,then Ag+ can be reduced by amino group of PCPA into silver nanoparticles.The binding force of silver particles and the substrate was effectively enhanced after PCPA modification.Finally,highly conductive silver-coated silica microspheres(1000 S/cm)were prepared through electroless silver plating.Compared with the dopamine modification method,the catechol-polyamine biomimetic modification method is low cost(1%of the cost of dopamine)and efficient(1/6 of the reaction time of dopamine).On this basis,the oxidant CuSO4/H2O2 was added to promote the oxidation of catechol to o-benzoquinone and accelerate the process of the deposition of PCPA.The deposition time of PCPA was shortened from 4 h to 40 min.The silver-coated silica microspheres with conductivity up to 1000 S/cm were prepared by subsequent electroless plating.Silver-coated silica microspheres filled silicone rubber composites show good mechanical properties and excellent electrical properties.The catechol/polyamine modification method have the advantages of high efficiency,controllability,and low-cost.The PCPA layer can serve as a platform for secondary functionalization.This modification method show broad application prospects in the field of surface modification and functionalization of materials.(2)We have modified the substrate of different shapes(fibrillar,spherical,sheet)and materials(polymers,metals,carbon materials)through catechol/polyamine surface modification,which proves that catechol/polyamine modification method is apply to various types of materials.Highly conductive(10000 S/cm)silver-coated aramid fibers were prepared by using catechol/polyamine modification and electroless silver plating,which can be used for electromagnetic shielding fabrics or flexible conductive materials.Aluminum and graphene were modified by catechol and polyamine.Then,a two-step electroless plating process was carried out to prepare silver coated aluminum and graphene.The silver-coated aluminum powder and silver-coated graphene show high electrical conductivity of 10000 S/cm.Silver-coated aluminum filled silicone rubber composites show good mechanical properties and excellent electrical properties.Moreover,ammonium persulfate as oxidant was added to accelerate the oxidation of catechol and promote the deposition of PCPA.The deposition time of PCPA on graphene was shortened to 1 h.The two-step silver plating method is suitable for the substrate which is difficult to be plated with silver.This method can be used to prepare highly conductive silver-coated powder,which provides a new idea for the metal surface of the material.The catechol/polyamine surface modification method does not limit the material and shape of the matrix,and has a great potential for application.(3)Stable polyphenol-metal film was quickly deposited on the surface of silica microspheres through chelation of tannic acid and ferric ions.The optimal deposition conditions were as follows:the reaction pH of 8,the concentration of Fe? of 0.10 g/L,the reaction time of 1 min.The pyrogallol groups and catechol groups in tannic acid has the function of absorbing and reducing silver ions.The adhesion of the silver particles were improved after TA-Fe? modification.TA-Fe? modified silica microspheres was coated with silver through electroless plating.The as-prepared silver-coated silica microspheres show electrical conductivity up to 1250 S/cm.The method of TA-Fe? modification is green,efficient,low cost,and has wide application range.It can be used for the secondary functionalization on its modified surface and has great industrial application prospect.