Construction,Light-steered Motion And Performance Of Multi-responsive Liquid Marbles

Liquid marble that a nonwetting droplet coated with hydrophobic particles can persist on solid and liquid surfaces.Due to the diversities of those coating particles and inner liquid,liquid marbles show some fascinating functions of movement and application,which can be driven by magnetic,light,electric field and surface tension,and also be used for environmental sensing,such as pH,temperature,surface tension etc.,as well as some special purposes like micro-reactors,cell culture and so on.Therefore,liquid marbles have shown broad application prospects in the fields of microdroplet manipulation and environmental sensing.However,the motional liquid marbles limited to a single drive mode with some inevitable drawbacks are difficult to adapt to complex environments.Similarly,the environment-sensitive liquid marbles based on a static sensing greatly limit their application fields,such as water analyses in large areas or fluidic pipelines.In view of those,two new types of liquid marbles are constructed based on the coated particles and inner solution,aiming at enriching the movement mode and optimizing the environmental application performance of liquid marbles.The main research results are given as follows:?1?We develop a near-infrared?NIR?light-driven magnetic liquid marble,and demonstrate a unique NIR light-steered method that can change phototaxis only by adjusting the light position.The magnetic liquid marble is constructed by oleic acid modified Fe₃O₄ nanoparticles?Fe₃O₄@OA NPs?.Based on the superparamagnetic feature of Fe₃O₄@OA NPs,the liquid marble can be moved by magnetic traction on water surface and substrates.By taking advantages of photothermal effect?absorbance of 0.63?of Fe₃O₄@OA NPs,a negative phototaxis occurs when the NIR light irradiates the lower hemisphere of the marble attributing to the Marangoni flow induced by a local temperature increase.Similarly,a switch to positive phototaxis happens when the irradiation position moves to the upper hemisphere stemming from the good transmittance?0.23?of the coated Fe3O4@OA NPs contributing to the regulation of the direction of Marangoni flow.The light/magnetic dual-responsive liquid marbles effectively enrich the movement mode and applied environment with the integrated advantages of light/magnetic and the switchable positive/negative phototaxis.?2?We firstly develop a dual-responsive liquid marble for NIR light and pH based on the photothermal property and hydrophobic-hydrophilic transformation in acid of the coated mixed stabilizers of hydrophobic carbon black?CB?particles and titanium dioxide particles modified with heptylamine?HA-TiO₂?particles,respectively.Among them,the responses of the liquid marble to NIR light and pH can be modulated by adjusting the mass ratio of CB and HA-TiO₂.For the optimal mass ratio of 0.4:1?CB:HA-TiO₂?determined in this paper,the detection range is pH?6.2,and the responsive time is kept within 2 min.In addition,benefiting from the excellent droplet manipulation,a new liquid marble is constructed that the inner pure liquid is replaced by TiO₂-Au micro-particles solution with an excellent photocatalytic performance for the first time,which can be released for environmental remediation at a ratio of more than 99%as long as the liquid marble collapses after moving to acidic environment because of their hydrophilia.This liquid marble breaks through the limitation of previous static sensing with new construction ideas,providing a new understanding for the application of liquid marble in environmental field.The results give new ways to the construction of liquid marbles from three aspects of constructing multi-functional coated particles,mixing various stabilizers and improving the monotonicity of inner solution,and also provide a guiding ideas for the light-driven mode and environmental application of liquid marbles.