Interfacial Structure And Properties Of Graphene/Polymer Composites

Graphene,a two-dimensional sp2-hybridized carbon,is currently,without any doubt,the most intensively studied material.This single-atom-thick sheet of carbon atoms arrayed in a honeycomb pattern is the world’s thinnest,strongest,and stiffest material,as well as being an excellent conductor of both heat and electricity.Due to its fascinating physical and chemical properties,graphene has been used in the field of electronics,energy storage,environment protection,medicine and pharmacology and catalyst design.Despite significant efforts and great progress made in the synthesis of new polymers,the properties of neat polymer compared to nano-filled polymer composites can be considered to be modest in many cases.As mentioned above,taking full advantage of the graphene to design and prepare high performance materials,will be an important developing trend for polymer composites.On the basis of reviewing the graphene based nanocomposites,functional polymer materials and their applications,this thesis is focused on exploring into the structure and high performance of graphene based polymer composites.Till now,the applications of graphene in polymer composites are mainly limited by the design of interfacial structure,uniform disperse of graphene and lack of complete understanding of the relationship between the structure and properties of the composites.As mentioned above,modification methods based on the interfacial interactions from strong level(covalent bonding)to weak level(π-π stacking,electrostatic attraction,hydrogen bond,CH-π、cation-π)have been discussed.In addition,the utilization of large surface area,high tensile strength,high carrier mobility,good optical transparency and excellent thermal conductivity of graphene under different interfacial interactions have also been investigated.The theoretical basis to prepare high performance graphene based polymer composites could be provided through the investigation of the relationship between interfacial structure and properties of the composites.In this dissertation,five different kinds of polymers that could be used in medicine and pharmacy,environmental protection,energy and new materials were studied.The main contents are shown as following:As the most important presoma to prepare graphene,graphene oxide(GO)also possesses large surface area and high tensile strength.Simple preparation processes make GO to exhibit unique advantages in polymer filling modification.As a conventional drug carrier,poly(sebacic anhydride)(PSA)possesses the advantage of surface erosion,however it cannot meet the requirements for long term drug release for chronic inflammation.Covalent modification cannot only enhance the dispersion of graphene,but also can advance the adhesion at the interface.Therefore,in chapter 2,GO-PSA composite based on-COO-bond and CH-π interfacial interactions was designed and prepared.Then,π-π stacking interaction between GO and levofloxacin(LOF)was utilized to fabricate LOF loaded pills.Finally,the in vitro release behavior of the pills was investigated under the conditions of 37℃,and pH=7.4(PBS).Compared to the pills containing pure PSA,the pills containing GO-PSA exhibited longer release time and zero order release behavior.This can be ascribed to the strong interaction between GO and PSA as well as the LOF.Though polyethylenimine(PEI)exhibit high adsorption capacity to CO2,it has a small surface area and volatility.Similar to graphene,GO has large surface area.In the GO-PSA composite,a small area was utilized to load LOF.To take full advantage of the large surface area,GO-PEI composite based on C-N bond,electrostatic attraction,hydrogen bond,CH-π and cation-π interfacial interactions was designed and prepared in chapter 3.Subsequently,the adsorption capacity,mechanism and cycles were investigated through various techniques.The results revealed that three dimensional structures could be obtained at low concentration of PEI,and the strong interfacial interactions make the composite more thermostable.All these are contributions to the high CO2 adsorption capacity and good cyclical stability.Besides large surface area,graphene also shows excellent bulk properties such as high carrier mobility and thermal conductivity.However,only surface area was utilized in the GO-PSA and GO-PEI composites.To utilize the electricity of graphene,in chapter 4 is dedicated to the design and preparation of conjugated copolymer grafted graphene(G-CP)based on C-C bond and intramolecular π-π stacking was designed and prepared.In this chapter,brominated chemically converted graphene(G-Br)were obtained with sonication for the first time.Then,conjugated monomer such as phenthiazine,fluorenen and thiophene was grafted to the surface of graphene.Optical and electrochemical properties of the G-CP composite were studied by UV,FL and CV.Finally,preliminary investigation of power conversion efficiency was carried out on photovoltaic devices based on G-CP.Though covalent modification can enhance dispersion and interfacial adhesion,challenges such as complicated fabrication procedures and consumption of large amount solvent reduce its competitiveness.Consequently,graphene modified polymer based on noncovalent interactions were investigated in the last two chapters.Waterborne polyurethane has been used widely in the field of leather finishing for its eco-friendly and glossy,however,bad solvent barrier and low tensile strength property limits its practical use.Therefore,in chapter 5,GO/WPU composite based on π-π stacking,hydrogen bonding and CH-π interactions was designed and prepared through self-assembly techniques.The obtained GO/WPU emulsion had excellent stability at room temperature,and the tensile strength,solvent barrier property and electrical conductivity of the GO/WPU composites were improved remarkably.These are profits from the well-dispersed of GO,and the formation of layered structure.Silicone rubber(SR)has been widely used in the field of LED encapsulant for its high resistance to yellowing and good optical transparency,however,SR has very low thermal conductivity and bad barrier property.Accordingly,RGO/SR composite based on hydrogen bonding and CH-π interfacial interactions was designed and prepared through simple solvent-exchange method in chapter 6.The effect of the interfacial interactions on the barrier properties,mechanical,optical,and especially the thermal properties were intensively investigated.The improvement in the properties was due to the formation of interconnected network in the composites.In this dissertation,five different kinds of polymers modified by GO or RGO were investigated,which extend the applications of graphene-based polymer composites.What’s more,different interfacial structure based on various interacting mechanisms were designed,which can deepen our understanding of structure-property relationship for these composites.Finally,the obtained results cannot only provide experimental evidence to corresponding theoretical approaches,but also can offer theoretical basis for preparing high performance graphene-based polymer composites.