摘要
Abstract
[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other regions are made hydrophobic via self-assembled monolayer films.The substrate is then immersed in a liquid and withdrawn at a constant speed,causing the liquid to selectively adsorb onto the hydrophilic regions,resulting in droplet microarrays.For droplets in equilibrium with a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.关键词
液滴微阵列/限域液体吸附/亲/疏水图案化基底/润滑近似/相场动力学Key words
droplet microarrays/confined liquid adsorption/hydrophilic/hydrophobic patterned substrates/lubrication approximation/phase-field dynamics分类
通用工业技术
