Liu Zhou,Wyss Hans M.,Fernandez-Nieves Alberto,Shum Ho Cheung
We study the dynamics of two pinned droplets under the influence of an applied electric stress. We find that at a sufficiently strong field, this stress is sufficient to induce contact of the droplets. Interestingly, upon such contact, the dynamic behavior sensitively depends on the separation distance between the droplets. Besides the classical “coalescence” regime, we identify two other dynamic regimes: “fuse-and-split” and “periodic non-coalescence.” In the “fuse-and-split” regime, the droplets first fuse to form a jet, which subsequently breaks up into two droplets. In the “periodic non-coalescence” regime, the droplets contact and bounce away periodically without coalescence. Further analysis indicates that while the electric stress stretches the droplets into shapes that depend on the initial droplet separation, the surface tension stress dominates over the electric stress as soon as the droplets touch. We show that the shapes of the contacting droplets determine their subsequent dynamics. Our work provides a rationale for understanding the interplay between surface tension and electric stresses that govern the behavior of charged droplets and could inspire new methods for characterizing emulsion stability and surfactant performance.
Zhou Liu,Xiangyu Fu,Bernard P. Binks,Ho Cheung Shum
In this work, we investigated the coalescence of liquid water marbles driven by a DC electric field. We have found that two contacting liquid marbles can be forced to coalesce when they are charged by a sufficiently high voltage. The threshold voltage leading to the electro-coalescence sensitively depends on the stabilizing particles as well as the surface tension of the aqueous phase. By evaluating the electric stress and surface tension effect, we attribute such coalescence to the formation of a connecting bridge driven by the electric stress. This liquid bridge subsequently grows and leads to the merging of the marbles. Our interpretation is confirmed by the scaling relation between the electric stress and the restoring capillary pressure. In addition, multiple marbles in a chain can be driven to coalesce by a sufficiently high threshold voltage that increases linearly with the number of the marbles. We have further proposed a simple model to predict the relationship between the threshold voltage and the number of liquid marbles, which agrees well with the experimental results. The concept of electro-coalescence of liquid marbles can be potentially useful in their use as containers for chemical and biomedical reactions involving multiple reagents.
Gas therapy has been limited in its application as a robust standalone antitumor strategy due to the restricted gas production and cytotoxicity. To address this challenge, we employed electrotoxic PtRu composite metal nano-berries (PR) loaded with various therapeutic gas donors to construct a groundbreaking electric field-induced cascade gas therapy (EGT) platform, which generated a great electro-stress storm at tumor sites, exerting electrotoxicity and immunity functions against solid tumors, including those of large volume, through three pathways. Initially, electric field stimulation effectively boosted the release rate and yield of therapeutic gases from the EGT platform. Further, gas molecules reacted with reactive oxygen species (ROS) to either form oxidation coordination (CO and ROS) or generate more potent therapeutic components (RNS produced from ROS and NO), contributing to an electro-stress storm that augmented the cytotoxic potential of the gas components. Subsequently, this electro-stress storm further activated the tumor immune response, identifying and capturing escaped tumor cells, which held significant implications for treating tumors, including non-solid tumors with indistinct boundaries. In summary, the EGT platform leveraged an electro-stress storm to achieve ablation of large volume solid tumors and suppressed metastatic tumors, paving new pathways for gas-based therapeutic strategies.
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