Preparation And Properties Of Gradient TMPTMA And SiO₂ Porous Materials By The Inclined Rotating Sol-gel Method

Gradient porous materials(GPM)is an important part of functional gradient materials.,Due to their internal components structure gradient change and there is no obvious interface in the material,they can effectively avoid the implosion hydrodynamic instability in inertial confinement fusion(ICF),solve the problem of high thermal stress in aeronautics and astronautics and realizes the compatibility between biological implants and tissues.Therefore,GPM has a broad potential application in the corresponding field.However,the existing methods for preparing gradient porous materials have many shortcomings,such as complex process,difficulty in realizing precise control of density gradient,etc.,which cannot meet the needs of ICF and other precision experimental research.On the basis of literature research,this thesis developed a new method for the preparation of gradient porous materials,namely the slope-rotation sol-gel method.This method is simple,efficient and can realize the precise control of density gradient.Gradient porous materials,such as polyacrylate and SiO2,were prepared via slope-rotation sol-gel method.Firstly,the formation mechanism of gradient sol was explained and verified by mathematical modeling theory and particle velocity imaging(PIV)flow field analysis.The velocity distribution equation and the distribution equation of shear stress were derived by infinitesimal method.According to the distribution equation of shear stress,the flow field distribution inside the tube was predicted.The fluids of high and low concentration were mixed by volume diffusion.The final solution concentration distribution formula was calculated for arbitrary cross section of the tube.The PIV flow field analysis was used to obtain the real-time flow field distribution of the fluid in the tube,which verified the correctness of the theoretical derivation and the feasibility of slope-rotation sol-gel method.On the basis of the theoretical simulation,slope-rotation sol-gel experiment device and preparation technology were established.Using UV curing technology to achieve the rapid gelation,gradient density polyethylene trimethylolpropane three methyl acrylate(TMPTMA)foam was successfully fabricated The scope of density gradient was 10?200 mg/cm3 gradient around 6 cm length with precisely control.The results show that from the bottom to the top of the sample,the pore size increases gradually,the specific surface area decreases gradually,and the sample density decreases linearly.The density and absorbance of TMPTMA gel presented a linear positive correlation,and the energy storage modulus of TMPTMA gradient foam material was 5.7?7.6 MPa under the oscillation load,which was 2?3 times of a single density foam.In order to further improve the mechanical properties of TMPTMA foam,the slope-rotation sol-gel method was used to fabricate the TMPTMA foam doped with SiO2 sub-microspheres.From the bottom to the top of the sample,the mass percentage of SiO2 sub-microspheres gradually decreased.The energy storage modulus of the TMPTMA foam doped with SiO2 sub-microspheres was greatly improved.Under the low-frequency loading,the energy storage modulus of the gradient doped sample could reach 9.5 Mpa,which was 3-4 times higher than that of the undoped foam sample.Under high frequency loading,the energy storage modulus of SiO2 sub-microspheres gradient doped foam reached 14.1 MPa,which was around 40%higher than that of the homogeneously doped sample.By optimizing the preparation process and technology,the density gradient SiO2 aerogel and its composites were further prepared by slope-rotation sol-gel method.The results showed that the gelation time could be controlled by controlling the amount of catalyst.The density gradient of the samples was 50?150 mg/cm3 and the specific surface area was 609.3?472.2 m2/g in the axial around 6 cm length.From the bottom to the top,the pore size of gradient SiO2 aerogel gradually inereased,the skeleton distribution gradually loosen,the density gradually decreased,the light transmittance increased,and the refractive index decreased.Gradient SiO2/TMPTMA composite material fabricated in one step by slope-rotation sol-gel method to enhance mechanical properties of SiO2 aerogel From the bottom to the top of the composite,its three-dimensional network skeleton gradually thicken,the number of pore structures gradually decreased,the specific surface area gradually increased,and the mass proportion of SiO2 gradually increased.Gradient SiO2/TMPTMA composite material not only maintained the high specific surface area characteristics of SiO2 aerogel,but also significantly improved the mechanical properties of SiO2 material,making its energy storage modulus increase by 4?6 times.High Z element doping is commonly used in ICF diagnosis,TiO2 gradient doped SiO2 aerogel was prepared.From bottom to top,the specific surface area of the sample increased,and the number of pore structures decreased gradually.In the near-infrared band,the absorbance of SiO2 aerogel doped with TiO2 significantly increased,and the enhanced absorbance gradually decreased from the top to the bottom of the sample.