Study On Preparation And Mechanical Properties Of Eu³⁺-indole Dynamically Crosslinked Silicone Rubber

Silicone rubber has been widely used in military,medical,electrical and other fields due to its excellent comprehensive properties.It has become an important research object in the field of high performance elastomer materials.Due to the limited space for performance design and improvement of silicone rubber with traditional cross-linked network structure,its application in national defense,military and other fields has certain limitations.Cationic-πdynamic non-covalent bond has attracted more and more attention from material researchers due to its dynamic reversibility and design flexibility,and has been applied to different material systems,giving new characteristics to traditional materials.In order to further expand the design space of silicone rubber materials,the cation-πdynamic non-covalent bond was introduced into the silicone rubber system,and a hybrid synergistic cross-linking silicone rubber system containing both covalent cross-linking and Eu³⁺-πdynamic non-covalent cross-linking was designed and prepared.The effect of the reversibility of Eu³⁺-πinteraction on the dynamic and static mechanical behavior of silicone rubber was studied.The results can provide reference for the design of new silicone rubber materials.Based on the fluorescence labeling of silicone rubber matrix,combined with laser confocal microscopy（LSCM）-3D-dimensional reconstruction technology,the dispersion morphology and network structure visualization of filler in silicone rubber composites were explored,which provides a new perspective for the enhancement mechanism and related research of nanofillers.The specific research conclusions are as follows:（1）Indole-based silicone rubber system（DTIN）with covalent crosslinking was designed and prepared.With mechanical properties as the reference object,the content of crosslinking agent（TETA）was determined to be 2 wt%,and the preparation process was ternary direct blending.At the same time,the preparation conditions of the system were determined to be120℃and 24 h.In addition,the influence of different content of epoxy indole monomer（IN）on its mechanical properties was also regulated.It was found that the increase of IN content led to the decrease of toughness of DTIN,and the strength first increased and then decreased.When the content of IN was determined to be 1（the molar ratio of IN to TETA）,the mechanical properties were the best,the elongation at break was 219.65%,and the tensile strength was 169.93 k Pa.Therefore,the preparation and properties of subsequent samples were studied on this basis.（2）The hybrid synergistic cross-linking silicone rubber system（DTIN-Eu）containing both covalent cross-linking and Eu³⁺-πnon-covalent cross-linking was prepared.The effect of the reversibility of dynamic non-covalent bonds on the mechanical behavior of silicone rubber was studied from two aspects of dynamic and static mechanical properties.The existence of Eu³⁺-πinteraction was successfully proved by EDS,liquid UV differential spectroscopy,fluorescence emission spectroscopy,quantum dynamics（QD）and all-atom molecular dynamics（MD）simulations,and the relative distance between them was 3.59?,which was consistent with the theoretical range of cation-πinteraction.Based on the elongation at break and tensile strength,it was determined that the mechanical properties were the best when the Eu³⁺addition（molar ratio to IN）was 1/2,and the tensile strength was 365.48 k Pa.Under the dynamic force,the Eu³⁺-πinteraction exhibits excellent reversibility under high alternating strain to maintain the relative stability of the material,and it is more obvious at high temperature.Under static force,the deformation stress decreases with the decrease of cyclic tensile rate.Under multiple cyclic loadings,the Mullins effect is obvious with the increase of temperature.Combined with Young’s modulus,stress softening energy loss and recovery hysteresis energy loss,it shows that the existence of Eu³⁺-πdynamic non-covalent bond can alleviate certain Mullins effect,and the reversibility of Eu³⁺-πinteraction is related to temperature and time.In addition,the formation of Eu³⁺-πinteraction can improve the creep resistance of silicone rubber system and accelerate its stress relaxation rate.（3）Based on the above two silicone rubber systems,silicone rubber composites were prepared by filling precipitated silica with different filler contents.The visualization of filler dispersion and filler network structure was successfully realized by reverse fluorescence labeling.The filled silicone rubber material has good fluorescence properties under the excitation wavelength of 405 nm,which meets the application conditions of LSCM.The aggregate size of the composites is concentrated in the range of 2000-4000 nm.With the increase of filler content,the filler dispersion is more uniform,and the filler network structure is more perfect and has good consistency with the increase of mechanical properties.At the same time,the experimental results show that even in the nanocomposites,the Eu³⁺-πinteraction still has a reinforcing and toughening effect on silicone rubber.The flexibility in the design of molecular network structure of silicone rubber materials is expected to give them adjustable and excellent performance.The relevant research results have important guiding significance for the design,improvement and application of the structure and performance of silicone rubber materials,and provide theoretical guidance for the design of high-performance,high-functional and high-intelligent polymer materials.