Visualization Of SiO₂ Filler Network Structures With Fluorescently Labeled In Silicone Rubber

In a complex use environment,the filler network structure of the rubber material undergoes elastic deformation,irreversible fracture and rearrangement,etc.,resulting in macroscopic mechanical behavior such as relaxation,creep,fatigue,and aging.These changes will reduce the component’s reliability.In severe cases,they can jeopardize the security of the system’s operation.In order to ensure the performance of rubber materials and their long-term stability,the systematic study of the structure-activity relationship between the filler network structure and macro-mechanical properties has aroused great attention in the field of materials.However,due to the complexity of the filler network structure,the current research methods and technical means are limited,making its real structure unclear.Therefore,there is a need for a technical means that can more easily and intuitively characterize the structure of the filler network,in order to detect its evolution under stress,and to provide theoretical and technical support for revealing the reinforcing mechanism of the filler.In this paper,sol-gel SiO₂,precipitated SiO₂ and silane coupling agent modified SiO₂ were in situ fluorescently labeled by"rare earth complex sensitization fluorescence enhancement technology";then scanning electron microscope,fluorescence spectrometer and laser scanning confocal microscope were used.Microscopes,rubber processing analyzers and solid rheology analyzers were used to determine and analyze the morphology and fluorescence properties of the fluorescently-labeled SiO₂ filler,as well as its filler network structure filled with silicone rubber,vulcanization properties,and dynamic mechanical properties.The specific conclusions are as follows:（1）In-situ fluorescent labeling of SiO₂ prepared by sol-gel method and precipitation method was realized by using the luminescent properties of rare earth ions and sensitized fluorescence enhancement technology of organic ligands.When 5%by weight of Eu（DBM）₃phen was used to fluorescently label SiO₂,the fluorescence intensity and excitation wavelength（405 nm）could be used to satisfy the use of laser scanning confocal microscope to ensure the reliability of visualization results.According to the visualization results,the dispersion state of the fillers,the morphology of the aggregates,the size of the aggregates of the filler,and the network connection rate in the fluorescent-labeled SiO₂ filled silicone rubber can be visually observed.Among them,the average size of 10-60 parts of sol-gel SiO₂ filled silicone rubber aggregates increased from 0.92μm to 6.04μm,and the network connection rate increased from 5%to 66%;the average size of 10-60 parts of precipitated SiO₂ filled silicone rubber aggregates increased from 2.12μm to 7.19μm,and the network connection rate increased from 8%to 73%.The results show that with the increase of the number of filled fillers,the network connection rate increases,and the internal structure of filled silicone rubber gradually forms a stronger filler network structure;（2）The rubber vulcanization performance,Payne effect and tensile property of the fluorescent-labeled SiO₂ filled silicone rubber were measured and analyzed by rubber processing analyzer and solid rheology analyzer.The results show that with the increase of filler loading,the torque value in the vulcanization process gradually increases,and the Payne effect gradually increases,which indicates that the interior of the filled silicone rubber gradually forms a strong filler network structure.The tensile fracture energy of 10-60 parts of sol-gel and precipitated SiO₂ filled silicone rubber increased from 83 J/m² to 210 J/m² and from 122 J/m² to 269 J/m²,respectively.Comparing the network connection rate with the tensile energy,it can be seen that the fillers filled with the silicone rubber filler network form a percolation filler of 30 parts each;（3）SiO₂ was modified in situ and fluorescently labeled with KH-550,KH-560,KH-570.Through the contact angle,binding adhesive test,filler aggregate size statistics and network connectivity analysis results,we can see that the hydrophobicity,dispersibility of SiO₂ filler and the compatibility with the silicone rubber matrix is the best modifier KH-570.