The coffee ring effect commonly exists in droplet deposition patterns, which fundamentally affects scientific research and industrial applications, like pharmaceutical purification, salt manufacturing, etc. Some researchers have tried different solutions to control the distributions of droplet deposition patterns, but most control deposits by adjusting droplet characteristics. In this work, droplet deposition patterns with different wettability are investigated by both localized and substrate heating. A whole process of droplet evaporation is recorded. The droplet generally evaporates from Constant Contact Radius (CCR) mode to Constant Contact Angle (CCA) mode, and CCR stage occupies the most of time. Experimental results show that, without any chemicals, laser induced local heating transitions particle deposition patterns from ring-like structure to dot-like patterns on a hydrophilic surface, driving most saline solvent to the center. Meanwhile, a hydrophobic surface is also investigated showing that the particles tend to assemble at the central area, but the pattern is slightly different compared to that on hydrophilic surface. In addition, physical mechanisms of local heating and heating from substrate are also explored.

中文翻译：

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不同加热方向对液滴沉积方式的影响

咖啡环效应通常存在于液滴沉积模式中，从根本上影响科学研究和工业应用，例如药物纯化，制盐等。一些研究人员尝试了不同的解决方案来控制液滴沉积图案的分布，但大多数通过调整液滴特性来控制沉积。在这项工作中，通过局部加热和基板加热研究了具有不同润湿性的液滴沉积方式。记录了液滴蒸发的整个过程。液滴通常从恒定接触半径（CCR）模式蒸发到恒定接触角（CCA）模式，而CCR台占据了大部分时间。实验结果表明，在没有任何化学物质的情况下，激光诱导的局部加热将颗粒沉积模式从环状结构转变为亲水表面上的点状模式，从而将大多数盐类溶剂驱至中心。与此同时，还研究了疏水表面，表明颗粒倾向于在中心区域聚集，但是与亲水表面上的图案相比，图案略有不同。另外，还探索了局部加热和从基板加热的物理机理。