Recktenwald Steffen M, Haward Simon J, Shen Amy Q, Willenbacher Norbert
Karlsruhe Institute of Technology, Institute for Mechanical Process Engineering and Mechanics, Gotthard-Franz-Straße 3, 76131, Karlsruhe, Germany.
Okinawa Institute of Science and Technology Graduate University, Micro/Nano/Biofluidics Unit, 1919-1 Tancha, Onna-son, Okinawa, 904-0495, Japan.
Sci Rep. 2019 May 8;9(1):7110. doi: 10.1038/s41598-019-43590-z.
Formation and breakup of fluid threads is pervasive in nature and technology, where high extensibility of fluid filaments and extended filament lifetimes are commonly observed as a consequence of fluid viscoelasticity. In contrast, threads of low viscous Newtonian fluids like water rupture quickly. Here, we demonstrate that a unique banding instability during filament thinning of model surfactant solutions, with a viscosity close to water and no measurable elasticity, leads to extremely long filament lifetimes and to the formation of remarkably long threads. Complementary measurements in planar extension as well as in shear reveal that this flow instability is characterized by a multivalued stress, arising beyond a critical strain rate, irrespective of flow kinematics. Our work reports the first observation of such phenomena during extensional deformation and provides a unifying view on instabilities in complex flow fields.
流体细丝的形成与破裂在自然界和技术领域中普遍存在，由于流体的粘弹性，通常会观察到流体细丝具有高延伸性和较长的细丝寿命。相比之下，像水这样的低粘性牛顿流体细丝会迅速破裂。在此，我们证明，在模型表面活性剂溶液细丝变细过程中存在一种独特的条带不稳定性，该溶液粘度接近水且无明显弹性，但却能产生极长的细丝寿命并形成极长的细丝。在平面拉伸以及剪切中的补充测量表明，这种流动不稳定性的特征是在超过临界应变率时会出现多值应力，而与流动运动学无关。我们的工作首次报道了在拉伸变形过程中此类现象的观察结果，并为复杂流场中的不稳定性提供了统一的观点。
