利用亲/疏水图案化基底限域吸附液体生成液滴微阵列的方法比传统微注射方法具有高效率的优势, 然而由于限域吸附过程涉及三相接触线钉扎、滑移的跨尺度动力学问题, 且吸附液滴边缘接触角极小、蒸发损失效应显著, 导致无论是通过理论还是基于实验都难以定量获取限域吸附液滴最大高度。该文首先通过相场动力学和润滑近似方法分别对亲/疏水图案化基底限域吸附液体过程进行了数值建模, 然后基于测量限域吸附溶液干燥后固体残留形貌的方法对限域吸附液滴最大高度进行了实验研究, 最后对比了理论和实验结果。研究结果表明, 2种数值建模方法均能模拟出限域吸附动力学过程的基本特征, 但相场动力学方法能够更准确地描述亲水区域吸附液滴最大高度随毛细数的变化规律, 有望用于指导液滴微阵列中液滴最大高度的精准调控。

Objective: Droplet microarrays are widely used in electronic device manufacturing, high-throughput cell screening, and microsensors. Unlike traditional micropipetting techniques, the confined adsorption method—using a hydrophilic/hydrophobic patterned substrate to generate droplet microarrays—offers higher efficiency through parallel processing. In this method, specific regions of a substrate are modified to be hydrophilic using methods like plasma treatment or vacuum ultraviolet irradiation, while other regions are made hydrophobic via self-assembled monolayer films. The substrate is then immersed in a liquid and withdrawn at a constant speed, causing the liquid to selectively adsorb onto the hydrophilic regions, resulting in droplet microarrays. For droplets in equilibrium with a specific hydrophilic surface, the maximum height is sufficient to fully characterize the droplet's shape and volume. Thus, controlling the maximum height allows for the regulation of droplet shape and volume. However, accurately quantifying the maximum height of confined liquid adsorption droplets is challenging, both theoretically and experimentally, because of the multiscale dynamics involved in the adsorption process. These challenges include issues such as three-phase contact line pinning and sliding, along with the extremely small contact angle at the droplet's edge, which leads to substantial fast evaporation losses. Although precise theoretical models and experimental data are available for idealized cases—such as infinitely large hydrophilic areas or infinitely long hydrophilic lines—these do not apply to more general scenarios. Specifically, when the lengths and widths of hydrophilic regions are comparable and both are smaller than the capillary length, no sufficiently accurate theoretical model exists. The lack of a precise model limits the systematic control of the maximum height of droplets in microarrays formed on hydrophilic regions. To address this gap, we developed a theoretical model and conducted numerical analysis to explore the maximum height of adsorbed droplets within hydrophilic regions smaller than the capillary length. Methods: The confined adsorption process on hydrophilic/hydrophobic substrates is numerically modeled using phase-field dynamics and lubrication approximation methods. Experimentally, the maximum height of the confined adsorption droplets is determined by measuring the residual surface morphology of the solid after drying the solution. High-speed imaging captures the liquid adsorption dynamics on hydrophilic patterns. Finally, the theoretical and experimental results are compared qualitatively and quantitatively. Results: The comparative results show that both the lubrication approximation and phase-field methods effectively simulate the two stages of liquid adsorption in hydrophilic regions. Compared with the phase-field method, the lubrication approximation method more accurately characterizes liquid bridge breakup and satellite droplet formation. Conversely, the phase-field method clarifies the relationship between the maximum droplet height and capillary number, revealing the weakening effect of viscous forces on droplet formation during confined adsorption. Conclusions: These findings offer valuable insights into the precise regulation of the maximum droplet height in confined adsorption-generated droplet microarrays.