Asaumi Yuta, Rey Marcel, Vogel Nicolas, Nakamura Yoshinobu, Fujii Syuji
Institute of Particle Technology, Friedrich-Alexander University Erlangen-Nürnberg, Cauerstrasse 4, 91058 Erlangen, Germany.
Langmuir. 2020 Mar 17;36(10):2695-2706. doi: 10.1021/acs.langmuir.0c00061. Epub 2020 Mar 4.
Liquid marbles are water droplets coated with solid particles that prevent coalescence and allow storage, transport, and handling of liquids in the form of a powder. Here, we report on the formation of liquid marbles that are stabilized entirely by a single monolayer of solid particles and thus minimize the amount of required solid material. As stabilizing particles, we synthesize relatively monodisperse, 80 μm-sized polystyrene (PS) particles coated with heptadecafluorooctanesulfonic acid-doped polypyrrole (PPy-CF) shell (PS/PPy-CF particles) by aqueous chemical oxidative seeded polymerization of pyrrole using FeCl as an oxidant and heptadecafluorooctanesulfonic acid as a hydrophobic dopant. We characterize the physicochemical properties of the particles as a function of the PPy-CF loading. Laser diffraction particle size analyses of dilute aqueous suspensions indicate that the polymer particles disperse stably in water medium before and after coating with the PPy-CF shell. X-ray photoelectron spectroscopy studies indicate the formation of a PPy-CF shell around the PS seed particles, which was further supported by deflated morphologies observed by scanning electron microscopy after extraction of the PS component from the PS/PPy-CF particles. We investigate the performance of the dried PS/PPy-CF particles to stabilize liquid marbles. Stereo- and laser microscope observations, as well as gravimetric studies, confirm that the PS/PPy-CF particles adsorb to the water droplet surface in the form of a particle monolayer with the characteristic hexagonal close-packed structure expected for spherical (colloidal) particles. Mechanical integrity of the liquid marble increases with an increase of PPy-CF loading of the PS/PPy-CF particles. The water contact angle of the PS/PPy-CF particles at air-water interface increases from 82 ± 12° to 102 ± 17° with an increase of PPy-CF loading. This increase in water contact angle directly correlates with the shape of the LM, with higher contact angles giving more spherical LMs. Furthermore, the broadband light absorption properties of the PPy coating was used to control evaporation rate of the enclosed water phase on demand by irradiation with a near-infrared laser. The evaporation rate could be finely controlled by the thickness of the PPy-CF shell of the particles stabilizing the liquid marbles.
液滴弹是涂覆有固体颗粒的水滴，这些固体颗粒可防止液滴聚结，并使液体能够以粉末形式进行储存、运输和处理。在此，我们报道了完全由单层固体颗粒稳定的液滴弹的形成，从而将所需固体材料的量降至最低。作为稳定颗粒，我们通过以FeCl为氧化剂、十七氟辛烷磺酸为疏水掺杂剂，对吡咯进行水相化学氧化种子聚合，合成了相对单分散的、80μm大小的聚苯乙烯（PS）颗粒，其包覆有十七氟辛烷磺酸掺杂的聚吡咯（PPy-CF）壳层（PS/PPy-CF颗粒）。我们将颗粒的物理化学性质表征为PPy-CF负载量的函数。对稀水悬浮液的激光衍射粒度分析表明，聚合物颗粒在包覆PPy-CF壳层之前和之后都能稳定地分散在水介质中。X射线光电子能谱研究表明在PS种子颗粒周围形成了PPy-CF壳层，从PS/PPy-CF颗粒中提取PS成分后通过扫描电子显微镜观察到的瘪塌形态进一步证实了这一点。我们研究了干燥的PS/PPy-CF颗粒稳定液滴弹的性能。立体显微镜和激光显微镜观察以及重量分析证实，PS/PPy-CF颗粒以颗粒单层的形式吸附到水滴表面，具有球形（胶体）颗粒预期的特征六方密堆积结构。液滴弹的机械完整性随着PS/PPy-CF颗粒中PPy-CF负载量的增加而提高。PS/PPy-CF颗粒在气-水界面的水接触角随着PPy-CF负载量的增加从82±12°增加到102±17°。水接触角的这种增加与液滴弹的形状直接相关，接触角越高，液滴弹越呈球形。此外，PPy涂层的宽带光吸收特性被用于通过近红外激光照射按需控制封闭水相的蒸发速率。蒸发速率可通过稳定液滴弹的颗粒的PPy-CF壳层厚度进行精细控制。
