First, the agent coats the oil, serving as a physical barrier between the droplets.一、乳化剂包裹住油滴，在油滴间形成一道物质屏障。
In the classic example, biologists imagine that a physical barrier arises, perhaps the formation of a new mountain range生物学家过去总是想像山脉隆起或者新海岛在海上冒出之类的地理隔离事件为例子。