Bossler Frank, Weyrauch Lydia, Schmidt Robert, Koos Erin
Karlsruhe Institute of Technology, Institute for Mechanical Process Engineering and Mechanics, Straße am Forum 8, 76131 Karlsruhe, Germany; KU Leuven, Department of Chemical Engineering, Celestijnenlaan 200f, 3001 Leuven, Belgium.
Karlsruhe Institute of Technology, Institute for Mechanical Process Engineering and Mechanics, Straße am Forum 8, 76131 Karlsruhe, Germany.
Colloids Surf A Physicochem Eng Asp. 2017 Apr 5;518:85-97. doi: 10.1016/j.colsurfa.2017.01.026.
The rheological properties of a suspension can be dramatically altered by adding a small amount of a secondary fluid that is immiscible with the bulk liquid. These capillary suspensions exist either in the pendular state where the secondary fluid preferentially wets the particles or the capillary state where the bulk fluid is preferentially wetting. The yield stress, as well as storage and loss moduli, depends on the size and distribution of secondary phase droplets created during sample preparation. Enhanced droplet breakup leads to stronger sample structures. In capillary state systems, this can be achieved by increasing the mixing speed and time of turbulent mixing using a dissolver stirrer. In the pendular state, increased mixing speed also leads to better droplet breakup, but spherical agglomeration is favored at longer times decreasing the yield stress. Additional mixing with a ball mill is shown to be beneficial to sample strength. The influence of viscosity variance between the bulk and second fluid on the droplet breakup is excluded by performing experiments with viscosity-matched fluids. These experiments show that the capillary state competes with the formation of Pickering emulsion droplets and is often more difficult to achieve than the pendular state.
通过添加少量与主体液体不混溶的第二流体，悬浮液的流变特性会发生显著改变。这些毛细管悬浮液要么以第二流体优先润湿颗粒的悬摆状态存在，要么以主体流体优先润湿的毛细管状态存在。屈服应力以及储能模量和损耗模量取决于样品制备过程中形成的第二相液滴的大小和分布。液滴破碎增强会导致更强的样品结构。在毛细管状态系统中，这可以通过使用溶解搅拌器提高湍流混合的速度和时间来实现。在悬摆状态下，混合速度的提高也会导致更好的液滴破碎，但在较长时间内，球形团聚更受青睐，从而降低屈服应力。结果表明，用球磨机进行额外混合对样品强度有益。通过使用粘度匹配的流体进行实验，排除了主体流体和第二流体之间的粘度差异对液滴破碎的影响。这些实验表明，毛细管状态与皮克林乳液液滴的形成相互竞争，并且通常比悬摆状态更难实现。
