Phase separating systems that are maintained away from thermodynamic equilibrium via molecular processes represent a class of active systems, which we call active emulsions. These systems are driven by external energy input, for example provided by an external fuel reservoir. The external energy input gives rise to novel phenomena that are not present in passive systems. For instance, concentration gradients can spatially organise emulsions and cause novel droplet size distributions. Another example are active droplets that are subject to chemical reactions such that their nucleation and size can be controlled, and they can divide spontaneously. In this review, we discuss the physics of phase separation and emulsions and show how the concepts that govern such phenomena can be extended to capture the physics of active emulsions. This physics is relevant to the spatial organisation of the biochemistry in living cells, for the development of novel applications in chemical engineering and models for the origin of life.

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活性乳液物理学

通过分子过程保持远离热力学平衡的相分离系统代表了一类活性系统，我们称之为活性乳液。这些系统由外部能量输入驱动，例如由外部燃料储存器提供。外部能量输入产生了无源系统中不存在的新现象。例如，浓度梯度可以在空间上组织乳液并导致新的液滴尺寸分布。另一个例子是活性液滴，它们会发生化学反应，从而可以控制它们的成核和大小，并且它们可以自发分裂。在这篇综述中，我们讨论了相分离和乳液的物理学，并展示了如何将支配这些现象的概念扩展到捕捉活性乳液的物理学。