Surface Interaction And Reinforcement Mechanism In Silicon Rubber Filled Silica

The high special strength of rubber nanocomposites come from the synergistic interactions of rubber molecule chain network and filler network. However, due to the intrinsic complexity of filler network and the restriction of analyzing techniques, the systematic experimental data of filler such as multi-scale structure and three dimensional distribution in the rubber matrix are still lack. The contribution of filler network to the mechanical properties and the physical mechanism of hard and soft double network coordinating role are described through some phenomenological methods.In this work, the synchrotron radiation X-ray nano-computed tomography(Nano-CT) technique combined with rheological and vulcanization research methods were used to study silicon rubber composites filled silica. Three types of silicon rubber/silica composites with different interactions from strong attraction to repulsion were developed through using different silica particles and surface modification. Astructure model of filler network mediated by bound rubber was proposed in rubber composites with attractive surface interaction. The structure evolution of filler network during deformation was observed. The relation between characteristic parameter of filler network and macro-mechanical properties was quantitatively analyzed. This work will promote a better understanding about filler reinforced microscopic physical mechanisms. The main results and conclusions are summarized as follows:1) The repulsive interaction strengths between silicon rubber and silica nanoparticles, ?pn, was controlled through varying surface chemistry of nanoparticles.Linear viscoelastic measurements of rubber composites show dramatic changes with?pn: an inclusion of ?2 vol% of nanoparticles(?pn = -5.2 kT) leads to a reduction in zero-shear viscosity of ? 15%,while the viscosity of rubber composites with ?pn =-0.36 kT can be well understood by hydrodynamic effect of nanoparticles with an adsorbed rubber layer at the interface. Theoretical analyses show a depletion layer surrounding nanoparticles with ? 2% surface coverage when surface interaction is strong repulsion,in contrast to ?100% surface coverage when ?pn= -0.36 kT. The results show that the low surface coverage in strong repulsive rubber composites can hardly assure an efficient load transfer between the rubber matrix and silica nanoparticles, leading to a reduction in viscosity.2) On the basis of the previous research results, two kinds of VMQ/SiO2 composites with interfacial adsorption were designed respectively. The difference of vulcanization behavior of VMQ/SiO2 composites with interfacial adsorption and interfacial repulsion was compared. The results demonstrate that under the same filler content, the higher bound rubber content the more obvious the inhibitory effect on vulcanization reaction. We propose a structure model of filler network: filler aggregates coated rubber molecule chain (bound rubber) on surface as a bridge connected to each other to form the filler network structure.3) Three-dimensional connected network of silica nanofiller was observed through in-situ synchrotron radiation X-ray nano-computed tomography (Nano-CT)technique. The structural evolution of silica nanofiller in silicone rubber matrix at different stains was investigated. The results show that Stress-induced phase separation between silica nanofiller and silicone polymer chain networks is observed during tensile deformation. The quantitative relationship between the structural parameters and the macroscopic mechanical properties of the filler network is analyzed. It is proved that the filler in the composite system acts as a reversible high functionality crosslinker. The reversible bonding between the filler and filler or filler and silicone rubber can effectively dissipate the mechanical energy and achieve the effect of enhancing mechanical properties.The main innovations involved in this thesis:1) The conformation and kinetic behaviors of the rubber molecule chains of interface layer in VMQ/SiO2 composites with strong repulsion surface interaction were quantitatively analyzed.2) The in-situ synchrotron radiation X-ray nano-computed tomography(Nano-CT) technique was employed to study the structural evolution of silica nanofiller in silicone rubber matrix at different stains. Stress-induced phase separation between silica nanofiller and silicone polymer chain networks is observed during tensile deformation.