低固相含量SiO2分散体系流变性研究

以甘油(GL)和聚乙二醇(PEG)为分散介质, 研究了低体积分数(Φ＜8%)的SiO₂分散体系的稳态和动态的流变性能, 发现体系都具有可逆的剪切变稀和剪切增稠现象. 在剪切速率大于临界剪切速率(γ^_.＞γ_^.c)时, 体系具有明显的剪切增稠现象, 而当γ^_.＜γ_^.c, GL体系只有轻微的剪切变稀现象, PEG体系剪切变稀现象却很明显. 在动态试验中考察了模量以及损耗角正切tg δ随剪切应力(σ)的变化. 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', tg δ大于1, 体系主要表现为粘性. 用“粒子簇”生成机理能较好地解释这种剪切变稀和剪切增稠现象, 即剪切变稀是由于连续的空间网络结构被破坏, PEG体系剪切变稀现象较GL体系明显应该与PEG高分子链的松弛以及体系中较少的氢键有关; 剪切增稠是由于粒子簇的生成引起的.

Study on the Rheological Behavior of SiO2 Dispersions with Low Volume Fraction

The rheological behavior of fumed silica dispersions in glycerol (GL) and polyethylene glycol (PEG) have been studied under steady and oscillation shear. The reversible shear-thinning and shear-thickening behaviors have been observed. The two dispersions all show obvious shear-thickening when the shear rate is higher than the critical rate (γ_^.＞γ_^.c), but when γ_^.＜γ_^.c, the GL system only shows slightly shear-thinning behavior, while the PEG system shows shear-thinning comparatively more obviously. The storage modulus G', loss modulus G" and tg δ have also been studied through oscillation stress shear. The magnitude of G" is larger than that of G' and tg δ＞1 for both of the systems in the range of stress studied, which shows that the systems mainly possess the viscous properties. Through “clustering” theory, the shear-thinning and the shear-thickening behaviors can be explained. The shear-thinning is due to the breakage of the steric continuous network structure and that the degree of the shear-thinning of the PEG system is larger than the GL system is due to the less number of the hydrogen bonds and the laxation of the PEG chains; the shear-thickening is caused by the formation of the clusters.