Effects of Light Dispersed Particles on the Stability of Dense Suspended Particles Against Sedimentation
Effects of Light Dispersed Particles on the Stability of Dense Suspended Particles Against Sedimentation
复制标题
轻分散颗粒对重悬浮颗粒抗沉降稳定性的影响
DOI：
10.1021/acs.jpcb.8b10172
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Corti, David S.
中科院分区：
文献类型：
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作者：
Yang, Yung-Jih;Franses, Elias I.;Corti, David S.
最近提出了一种新方法，其中双链阳离子表面活性剂 DDAB（双十二烷基二甲基溴化铵）的囊泡分散体稳定高密度二氧化钛颗粒的悬浮液（Yang, Y.-J; Corti, D.S.; Franses, E. I.Langmuir2015, 31, 8802–8808）。在足够高的 DDAB 浓度下，囊泡形成紧密堆积的结构，对二氧化钛颗粒的沉降提供强大的抵抗力，同时分散体保持高度剪切稀化和适度的极限粘度。在这里，为了阐明囊泡或其他非沉降颗粒稳定高密度颗粒以防止沉降的机制的关键因素，我们使用布朗动力学模拟（BDS）来检查自行快速沉降的“致密颗粒”和代表非沉降“刚性囊泡”的“轻颗粒”混合物的沉降行为。 BDS 证实，对于足够大的轻粒子体积分数 ψ2 值，致密粒子应保持悬浮状态。混合物的流变行为也使用 BDS 进行计算。观察到的轻颗粒分散体的剪切稀化行为表明，致密颗粒的悬浮液在高剪切应力下仍然是可流动的。此外，随着 phi2 的增加，致密粒子周围的轻粒子的局部粘度显着增加，特别是当 BDS 中施加的相同重力施加在致密粒子上时。轻粒子围绕移动的致密粒子的排列是决定致密粒子抗沉降稳定性的重要因素。 BDS 结果表明，非沉降颗粒的分散提供了一种稳定高密度颗粒沉降的通用方法。
A novel method in which vesicular dispersions of the double-chain cationic surfactant DDAB (didodecyldimethylammonium bromide) stabilize suspensions of high density titania particles was recently presented (Yang, Y.-J; Corti, D.S.; Franses, E. I.Langmuir2015, 31, 8802–8808). At high enough DDAB concentration, the vesicles form a close-packed structure, providing strong resistance to the sedimentation of the titania particles, while the dispersions remain highly shear-thinning with moderate limiting viscosities. Here, to elucidate the key factors of the mechanism by which vesicles or other nonsettling particles stabilize high density particles against sedimentation, we use Brownian dynamics simulations (BDS) to examine the sedimentation behavior of mixtures of “dense particles” that settle rapidly on their own and “light particles” that represent nonsettling “rigid vesicles”. BDS confirm that for large enough values of the volume fraction ϕ2of the light particles, the dense particles should remain suspended. The rheological behavior of the mixtures is also computed with BDS. The observed shear-thinning behavior of the light particle dispersion suggests that the suspensions of the dense particles are still flowable at high shear stresses. Furthermore, the local viscosity of light particles around the dense particles significantly increases with increasing ϕ2, particularly when the same gravitational force applied in the BDS is exerted on a dense particle. The arrangement of light particles around the moving dense particles is an important factor in determining the stability of the dense particles against sedimentation. The BDS results indicate that dispersions of nonsettling particles provide a general method for the stabilization against sedimentation of high density particles.