We study the dynamics of an active gel droplet with imposed orientational anchoring (normal or planar) at its surface. We find that if the activity is large enough droplets subject to strong anchoring spontaneously start to rotate, with the sense of rotation randomly selected by fluctuations. Contractile droplets rotate only for planar anchoring and extensile ones only for normal anchoring. This is because such a combination leads to a pair of stable elastic deformations which creates an active torque to power the rotation. Interestingly, under these conditions there is a conflict between the anchoring promoted thermodynamically and that favoured by activity. By tuning activity and anchoring strength, we find a wealth of qualitatively different droplet morphologies and spatiotemporal patterns, encompassing steady rotations, oscillations, and more irregular trajectories. The spontaneous rotations we observe are fundamentally different from previously reported instances of rotating defects in active fluids as they require the presence of strong enough anchoring and entail significant droplet shape deformations.

中文翻译：

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主动凝胶液滴中锚定驱动的自发旋转

我们研究了在其表面施加定向锚固（法向或平面）的活性凝胶滴的动力学。我们发现，如果活动足够大，则受到强锚定作用的液滴会自发地开始旋转，而旋转的感觉是由波动随机选择的。收缩性液滴仅在平面锚固时旋转，而可拉伸液滴仅在常规锚固时旋转。这是因为这样的组合会导致一对稳定的弹性变形，从而产生有效的转矩来为旋转提供动力。有趣的是，在这些条件下，在热力学上促进的锚定与活性促进的锚定之间存在冲突。通过调整活动和锚定强度，我们发现了许多质量上不同的液滴形态和时空模式，包括稳定的旋转，振荡，以及更多不规则的轨迹 我们观察到的自发旋转与以前报道的活性流体中旋转缺陷的情况根本不同，因为它们需要存在足够强的锚固并需要显着的液滴形状变形。