Precise Droplet Manipulation Based on Surface Heterogeneity

Abstract

Conspectus The control of droplet behavior has been investigated for several centuries due to its universality and significance in nature, daily life, and industrial applications. Diverse strategies have been developed and employed to regulate droplet behavior, and great progress has been achieved such as accelerated droplet bouncing, controlled droplet dispensing, and enhanced droplet adhesion. Compared with the strategies utilizing external fields including magnets, heat, light, and electricity as well as various topological structures, the heterogeneous wettability surface provides a facile and efficient way to manipulate droplet behavior and thus has aroused increasing research interest in many fields. The heterogeneous wettability substrate integrates wettable and less wettable regions onto an individual surface, with rational design and a geometrical arrangement. Therefore, it shows more precise, diverse, and controllable interactions with droplets than homogeneous surfaces. In addition to confining the droplet position and morphology and regulating the droplet dynamics, the nonuniformity in wettability can induce a difference in electrical conductivity, nucleation energy barriers, and so forth, which greatly extends its application in the fields of functional materials deposition and device fabrication. In this Account, recent progress in the precise droplet manipulation based on heterogeneous wettability is summarized. First, the principle of droplet control by a heterogeneous surface and the development of the green printing technique based on this principle are introduced. Then the droplet manipulation, categorized as droplet patterning, droplet isolation, and droplet dynamics, is described. Meanwhile, related applications, such as high-capacity information coding, highly sensitive detection, and high-performance optic/electric device fabrication, are demonstrated. In addition, the general principle for controlling the droplet impact using heterogeneous wettability substrates is highlighted. Finally, a brief summary of this Account, with challenges and opportunities in this field, is proposed.

Non‐Hookean Droplet Spring for Enhancing Hydropower Harvest

“…Inspired by lotus leaves and beetles, wettability, especially heterogeneous wettability, provides an effective way to manipulate droplet behaviors. [19][20][21][22][23][24][25] In this work, we fabricate droplet-based springs using two parallel plates with heterogeneous wettability, and investigate their non-Hookean elastic mechanics under pressing and stretching. We demonstrate that the nonlinear behaviors of the spring can be well manipulated by the droplet volume, droplet number, and especially the wettability patterns on the parallel plates.…”

Hierarchically Structured, All-Aqueous-Coated Hydrophobic Surfaces with pH-Selective Droplet Transfer Capability

“…Surfaces with programmable droplet adhesion have propelled technology in both fundamental research and applications, such as droplet-based reactions in microfluidics, precise sensing and analysis in lab-on-a-chip systems, and efficient fog harvesting. − Research in droplet manipulation typically employs external stimuli, including magnetic, − electric, , acoustic, , and photo-actuation. − However, these approaches rely on the stimulus application, droplet functionality, or involve active handling and thus have limitations for autonomous, self-guided environmental applications. In contrast, surfaces that can “recognize” droplet environments (acidity or presence of chemicals) and autonomously “act”, that is, adjust droplet adhesiveness in response to the environment, are self-regulated, do not require power sources, and are more suitable for autonomous operation and monitoring of reactions in the droplets or in applications for water harvesting.…”

“…Surfaces with programmable droplet adhesion have propelled technology in both fundamental research and applications, 1 such as droplet-based reactions in microfluidics, precise sensing and analysis in lab-on-a-chip systems, and efficient fog harvesting. 2−7 Research in droplet manipulation typically employs external stimuli, 8 including magnetic, 9−11 electric, 12,13 acoustic, 14,15 and photo-actuation.…”

Microfluidics-Enabled Soft Manufacture of Materials with Tailorable Wettability

“…In droplet microfluidics, the generation of water-in-oil (W/O) emulsions requires hydrophobic channels while the generation of oil-in-water (O/W) emulsions needs hydrophilic channels to prevent the adhering of discrete droplets to the channel walls . The channel wettability also plays a significant role in bubble management. , The ability to dynamically tune surface wettability has led to the emergence of digital microfluidics, such as by electrowetting/dewetting control − or creating surface anisotropy − for liquid manipulation. In parallel, paper-based microfluidics relies on patterning hydrophobic boundaries around hydrophilic channels on papers to control fluid transport for low-cost diagnosis. , These examples demonstrate the widespread applications of wettability control in microfluidics.…”