不稳定冻胶中的指进到压裂转变
Fingering to fracturing transition in a transient gel
摘要：
断裂过程在软材料中是普遍存在的，甚至在复杂的流体中，受到应力。为了研究这些过程中的一个简单的几何形状，我们使用一个模型自组装瞬态凝胶和研究的不稳定模式时，低粘度的油推动更粘稠的瞬态凝胶在径向海勒-肖细胞。由于形态的图案的分析，我们发现一个不连续的过渡之间的标准Saffman-Taylor指进不稳定性和压裂不稳定性的石油注入率的增加。我们的数据表明，手指尖前面的凝胶的流动特性控制向压裂的过渡。通过分析的手指和裂缝附近的凝胶的位移场，我们表明，在指状制度，石油轻轻地推动凝胶，而在压裂制度，裂缝撕裂凝胶，导致在一个强大的下降的凝胶速度提前裂纹尖端相比，尖端速度。我们发现了一个独特的行为，为整个位移场的凝胶周围的裂纹，这是显着不同的手指，并揭示了在短时间内的固体状行为的凝胶。我们的实验和分析提供了定量而简单的工具，明确区分手指从裂纹的粘弹性材料。
英文摘要：
Fracture processes are ubiquitous in soft materials, even in complex fluids, subjected to stresses. To investigate these processes in a simple geometry, we use a model self-assembled transient gel and study the instability patterns obtained in a radial Hele-Shaw cell when a low viscosity oil pushes the more viscous transient gel. Thanks to an analysis of the morphology of the patterns, we find a discontinuous transition between the standard Saffman-Taylor fingering instability and a fracturing instability as the oil injection rate increases. Our data suggest that the flow properties of the gel ahead of the finger tip controls the transition towards fracturing. By analyzing the displacement field of the gel in the vicinity of the fingers and cracks, we show that in the fingering regime, the oil gently pushes the gel, whereas in the fracturing regime, the crack tears apart the gel, resulting in a strong drop of the gel velocity ahead of the crack tip as compared to the tip velocity. We find a unique behavior for the whole displacement field of a gel around a crack, which is drastically different from that around a finger, and reveals the solid-like behavior of the gel at short time. Our experiments and analysis provide quantitative yet simple tools to unambiguously discriminate a finger from a crack in a visco-elastic material.
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