Bazazi Parisa, Stone Howard A
Department of Petroleum Engineering, Colorado School of Mines, Golden, CO 8040-1, USA.
Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, NJ 08544, USA.
Soft Matter. 2025 Feb 12;21(7):1296-1307. doi: 10.1039/d4sm00618f.
The capillary break-up of complex fluid filaments occurs in many scientific and industrial applications, particularly in bio-printing where both liquid and polymerized droplets exist in the fluid. The simultaneous presence of fluid and solid particles within a carrier fluid and their interactions lead to deviations in the filament break-up from the well-established capillary breakup dynamics of single-phase liquids. To examine the significance of the dispersed phase and the internal interactions between liquid droplets and solid particles, we prepare emulsions through photopolymerization and conduct experimental investigations into the pinch-off dynamics of fluid filaments, focusing on the impact of varying concentrations of liquid droplets (before polymerization) and polymerized droplets. Despite the increase in bulk viscosity due to the presence of polymerized droplets in the fluid and their aggregation, the results show that polymerization significantly reduces the length of the fluid filament before breakup, thus shortening the duration of pinch-off. We investigate two categories of complex fluids, characterized by their droplet sizes: (i) sub-micrometer droplets and (ii) droplets with an average diameter of 50 micrometers. In emulsions containing sub-micrometer droplets, the individual droplet contributions remain undetectable during capillary breakup, and the measured pinch-off dynamics predominantly reflect the bulk shear viscosity or viscoelasticity of the system. This is due to the droplet sizes falling below our imaging resolution. In contrast, emulsions with larger polymerized droplets exhibit behavior analogous to single-phase carrier fluids: once the filament's length equals the droplet diameter, the droplets are expelled. Concurrently, larger liquid droplets are deformed and elongated along the flow direction. Our study highlights the effect of mixing liquid and polymerized droplets on the capillary breakup dynamics of fluid filaments, providing insights to formulate 3D printing inks.
复杂流体细丝的毛细管破裂现象出现在许多科学和工业应用中，特别是在生物打印领域，其中流体中同时存在液体和聚合液滴。载液中流体和固体颗粒的同时存在及其相互作用导致细丝破裂偏离了单相液体已确立的毛细管破裂动力学。为了研究分散相的重要性以及液滴与固体颗粒之间的内部相互作用，我们通过光聚合制备乳液，并对流体细丝的 pinch-off 动力学进行实验研究，重点关注不同浓度的液体液滴（聚合前）和聚合液滴的影响。尽管由于流体中聚合液滴的存在及其聚集导致本体粘度增加，但结果表明聚合显著缩短了破裂前流体细丝的长度，从而缩短了 pinch-off 的持续时间。我们研究了两类以液滴大小为特征的复杂流体：（i）亚微米级液滴和（ii）平均直径为 50 微米的液滴。在含有亚微米级液滴的乳液中，在毛细管破裂过程中单个液滴的贡献仍无法检测到，测量的 pinch-off 动力学主要反映了系统的本体剪切粘度或粘弹性。这是因为液滴尺寸低于我们的成像分辨率。相比之下，含有较大聚合液滴的乳液表现出类似于单相载液的行为：一旦细丝长度等于液滴直径，液滴就会被排出。同时，较大的液体液滴会沿流动方向变形和拉长。我们的研究突出了混合液体和聚合液滴对流体细丝毛细管破裂动力学的影响，为配制 3D 打印墨水提供了见解。
