Designed microtextured surfaces have shown promising applications in tuning the wettability of a liquid droplet on the surfaces and attracted great attention over the past decade;unfortunately, the effect of surface geometry on wetting properties is still poorly understood. In this work, two- and multi-stage pillar microtextures are designed to construct gradient surfaces by altering pillar width and spacing. Then, the multi-phase lattice-Boltzmann method (LBM) is used to investigate the wetting dynamics of a liquid droplet on the gradient surface. Results show that for the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis is found to be proportional to the roughness gradient when droplet/surface system is in the Cassie-Baxter state. However, this proportional relation is no longer correct when the system is in the transition state between the Wenzel and Cassie-Baxter states. For the two-stage gradient surface with variable pillar spacing, the contact angle hysteresis always increases linearly with increasing roughness gradient. Results also show that when a larger droplet is placed on the multi-stage gradient surface, stronger droplet motion is observed due to the smaller contact angle hysteresis. The present LBM simulations provide a guideline for the design and manufacture of the microtextured surfaces to tune the droplet wettability and motion.%本文通过改变肋柱宽度和间距，构造了二级和多级梯度微结构表面，采用格子-Boltzmann方法对液滴在两种梯度表面上的铺展过程进行了研究，探析液滴运动的机理和调控方法。结果表明，在改变肋柱间距的二级梯度表面上，当液滴处于Cassie态时，接触角滞后大小与粗糙度梯度成正比关系；当液滴从Cassie态转换为Wenzel态或介于两者之间的不稳定态时，这一正比关系不再遵循。在改变肋柱宽度的二级梯度表面上，接触角滞后大小与粗糙度梯度始终成正比关系。在多级梯度表面上，随液滴初始半径增大，接触角滞后减小，但液滴平衡位置相较于初始位置偏离增大。对梯度微结构表面上液滴运动和接触角滞后的定量分析，可为实现梯度微结构表面液滴运动调控提供理论依据。
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