Optofluidics and Interface Science Laboratory, Department of Physics, National Institute of Technology Calicut, Kozhikode, Kerala India, 673601.
Langmuir. 2022 Sep 27;38(38):11743-11752. doi: 10.1021/acs.langmuir.2c01880. Epub 2022 Sep 15.
Liquid marbles (LMs), droplets encapsulated with micro/nanoparticles, have attracted significant attention owing to their potential applications in various fields, ranging from microbioreactors to sensors. The volume of the LMs is a key parameter determining their mechanical stability and gas sensing ability. It is ideal to work with small volumes because of their better mechanical stability and gas sensing power compared to the larger LMs. Though many methods exist for producing LMs in the volume range above 2 μL, no reliable method exists to prepare fully coated submicroliter LMs with tunable volume. The situation becomes even more difficult when one attempts to produce tiny Janus Liquid Marbles (JLMs). This paper presents a simple, single-step, and efficient strategy for obtaining both the pristine LMs and JLMs in the volume range 200 nL to 18 μL. The core idea relies on the impact of a liquid drop on a particle bed at a Weber number of ∼55 to produce two daughter droplets and to convert these droplets into LMs/JLMs. The whole process takes only a few tens of milliseconds (∼50 ms). We have rendered the experimental schemes so that both the JLMs and pristine LMs can be produced in a single step, with control over their volume. The mechanical stability analysis of the prepared marbles indicates that 200 nL is 5 times more stable than 10 μL of LMs. The 0.72 μL LMs prepared with a 0.5 v/v % phenolphthalein indicator solution showed 3 times faster response time to ammonia gas sensing than 10 μL of LMs. The results presented in this work open up a new route for the rapid and reliable production of both multilayered LMs and JLMs with tunable volume in a wide range (200 nL to 18 μL).
液滴（LM）是用微/纳米颗粒包裹的液滴，由于其在微生物反应器到传感器等各个领域的潜在应用而受到了极大的关注。LM 的体积是决定其机械稳定性和气体传感能力的关键参数。由于与较大的 LM 相比，其具有更好的机械稳定性和气体传感能力，因此使用较小的体积是理想的。尽管有许多方法可以在 2 μL 以上的体积范围内产生 LM，但目前还没有可靠的方法来制备具有可调节体积的完全涂覆的亚微 LM。当试图制备微小的单分体液滴时，情况会变得更加困难。本文提出了一种简单、单步、高效的策略，可在 200 nL 至 18 μL 的体积范围内获得原始 LM 和单分体液滴。其核心思想依赖于在韦伯数约为 55 的情况下，液滴撞击颗粒床产生两个子液滴，并将这些液滴转化为 LM/单分体液滴。整个过程只需几十毫秒（约 50 ms）。我们设计了实验方案，使得单分体液滴和原始 LM 可以在一个步骤中生成，并且可以控制它们的体积。制备的液滴的机械稳定性分析表明，200 nL 的液滴比 10 μL 的 LM 稳定 5 倍。使用 0.5 v/v%酚酞指示剂溶液制备的 0.72 μL 的 LM 对氨气的传感响应时间比 10 μL 的 LM 快 3 倍。本工作中所呈现的结果为快速可靠地制备具有可调体积（200 nL 至 18 μL）的多层 LM 和单分体液滴开辟了一条新途径。
