分散介质和温度对SiO_2分散体系流变性能的影响

Effect of suspending medium and temperature on the rheological properties of SiO_2 dispersions

用应力控制流变仪考察了不同分散介质乙二醇(EG)、丙二醇(PG)、丁二醇(BG)以及温度对SiO2分散体系流变性能的影响。实验结果表明:以不同分散介质制得的分散体系都具有可逆的剪切变稀和剪切增稠现象,且在所研究的应力范围内,体系中耗能模量G″都大于储能模量G′,体系主要表现为粘性;在剪切变稀区,G′明显减小,其中EG体系的G′减小最明显,PG体系次之,BG体系G′减小最少,而G″基本保持不变;在剪切增稠区,G′和G″都随着应力的增大而增大。用“粒子簇”生成机理能较好地解释这种流变现象,即:剪切变稀与体系中连续空间网络结构的破坏有关,而剪切增稠则是流体作用力促使不稳定的“粒子簇”的生成所致;分散介质粘度大的体系,对应的临界剪切应力σc反而小,在频率扫描中,临界频率cω也具有相同的变化规律;改变温度并不会改变体系的cσ和流变曲线的变化趋势,但曲线会上下平移。

The influence of the suspending medium of EG, PG, BG and temperature on the rheological properties of silica dispersions was studied with a stress controlled rheometer. The results show that the systems have reversible shear thinning and shear thickening behaviors, and the magnitude of loss modulus G＂ is larger than that of storage modulus G＇ for these suspensions in all the range of stress, which shows that these suspensions mainly possess viscous property. When σ〈σc, G＇ decreases significantly, and the sequence of the decreasing degree （from large to small） of G＇ is. EG/SiO2, PG/SiO2 and BG/SiO2, meanwhile G＂ almost remains unchanged; while σ〈σc, G＇ and G＂ increase with the increase of the shear stress. Using ＂clustering＂ theory, the shear-thinning and the shear-thickening behaviors can be explained, i. e. , shear-thinning is due to the breakage of the steric continuous net-work structure and shear-thickening is caused by the formation of the clusters due to the hydrodynamic forces. Critical stress σc of the suspension is larger while the viscosity of the suspending medium is lower. Different temperatures don＇t change σc and the trends of the rheological plot almost remain unchanged except that the rheological plots move vertically when the temperature changes.