Preparation Of Epoxy Resin Porous Materials By Reaction-induced Phase Separation Regulated Using SiO₂ Particles

Most of the research on the use of solid particles to regulate the phase separation process of polymer systems in order to improve the distribution of the two-phase components has focused on polymer modification,while little research has been reported on the involvement of solid particles in the fine regulation of the microstructure of porous materials.In this project,SiO₂ particles are introduced to fine regulation the microstructure of epoxy resin porous materials（through-hole and closed-hole structures）during the preparation of epoxy resin porous materials by reaction-induced phase separation,where the SiO₂ particles can also be removed by acid etching.The results of this study are universal and instructive for the preparation of polymeric porous materials by the participation of solid particles in phase separation.（1）Preparation of epoxy resin porous materials by reaction-induced phase separation with SiO₂ particles.A reaction-induced phase separation method was used to add hydrophilic（C.A.=0^o）SiO₂ particles with size of 7-40 nm into the epoxy resin blend system.By comparing the reaction kinetics,phase separation kinetics and final phase structure of the epoxy resin blend system before and after the addition of fumed SiO₂ particles,it is found that the fumed SiO₂ particles preferfully disperse in the pore-enrichment phase.On the one hand,it makes the system more viscoelastic,reduces the mass transfer rate,decreases the reaction rate and delays the gelation point.On the other hand,the rate of coarsening of the phase structure is reduced and the final phase structure is frozen in the early stages of phase separation.For the degradation of phase separation by spinodal lines,the freezing state of the phase structure can be finely tuned by varying the mass fraction of fumed SiO₂ particles to obtain epoxy porous materials with a continuous through-hole structure within the investigable range.（2）Preparation of through-hole epoxy resin porous materials from SiO₂ particles with modulated phase separation.The monodisperse SiO₂ particles with different particle sizes（fumed,150 nm and 350 nm）were prepared by St?ber method.The surface of the SiO₂particles was modified with hexamethyldisilazane（HMDS）to obtained different wettability（C.A.=0^o,C.A.=93^o,C.A.=149^o）SiO₂ particles.SiO₂ particles with different mass fractions（1wt%,2wt%,3wt%）,particle sizes and wettability were introduced into the epoxy resin blend system respectively,and the system still followed the spinodal line degradation phase separation path,and it was found that:（1）The pore size of the through-hole material becomes progressively smaller as the mass fraction of SiO₂ particles increases due to the preferential dispersion of SiO₂ particles in the porogenic enriched phase;（2）The pore size of the through-hole material decreases as the SiO₂ particle size decreases due to the larger specific surface area of the small size SiO₂ particles,which increases the intermolecular interaction forces of the system;（3）As different wettability SiO₂ particles are compatible with the system,when the SiO₂ particles are preferentially wetted by one of the phases,then the effect of this phase on the microstructure of the epoxy resin porous material is more significant.（3）Preparation of closed-hole epoxy resin porous materials by SiO₂ particles with modulated phase separation.Epoxy resin porous materials（closed-hole structure and through-hole structure）were prepared by adding SiO₂ particles with different contents（1wt%,2 wt%,3 wt%）,wettability（C.A.=0^o,C.A.=93^o,C.A.=149^o）and particle sizes（fumed,150 nm,200 nm and 350 nm）to the same closed-hole epoxy resin blend system.The system follows the nucleation and growth phase separation process.The results show that:（1）The addition of different contents（0-10 wt%）of fumed and 350 nm SiO₂ particles resulted in the same phase separation pathway,but with the curing reaction,the nucleation rate of the system containing SiO₂ particles became faster and the structure tended to form bicontinuous from closed pores,indicating that SiO₂ particles would accelerate the coarsening rate of the epoxy resin blend system and the pore size of the material gradually decreased with the increase of SiO₂ particle content;（2）The different wettability SiO₂ particles produce an anchoring effect on the surface of the epoxy substrate and leave small pits after acid etching.Closed pores with different pore sizes were prepared by adjusting the content of porogenic agent,when the same amount of fumed SiO₂ particles is added to different closed-hole epoxy resin blend system,it is found that the cloud point and gel point of the systems containing fumed SiO₂ particles are delayed,and the quasi-phase diagram of the system can be drawn by this phenomenon.