Phoretic motion of particles along a temperature gradient formed in a fluid, known as thermophoresis, often takes place under the influence of bulk motion caused by thermal convection. In this paper, using a laser heating method, the significance of two competing effects, that is, thermophoresis and thermal convection, for the particle transport in a liquid phase confined in a microgap is investigated experimentally by changing the gap size as a control parameter. It is found that there is a threshold of the gap size, above which the particles tend to accumulate around the heated spot, forming a ring-like particle distribution. On the contrary, if the gap size is below the threshold, the particles are depleted from the heated spot. Switching between these accumulation and depletion modes is expected to develop novel manipulation techniques.

中文翻译：

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可变尺寸微间隙中液体悬浮液的激光诱导热泳和热对流之间的切换

粒子沿流体中形成的温度梯度的泳动运动，称为热泳，通常在热对流引起的整体运动的影响下发生。在本文中，使用激光加热方法，通过改变间隙尺寸作为控制参数，实验研究了两种竞争效应，即热泳和热对流，对于限制在微间隙中的液相中的粒子传输的重要性。发现间隙尺寸存在一个阈值，高于该阈值时，粒子往往会聚集在加热点周围，形成环状粒子分布。相反，如果间隙尺寸低于阈值，则粒子从热点中耗尽。在这些积累和消耗模式之间切换有望开发新的操作技术。