The abrupt behaviors of microdroplets during the LN-based photovoltaic manipulation may cause the transient instability and even failure of the microfluidic manipulation. In this paper, we perform a systematical analysis on the responses of water microdroplets to laser illumination on both naked and PTFE-coated LN:Fe surface, and find that the abrupt repulsive behaviors of the microdroplets are due to the electrostatic transition from the dielectrophoresis (DEP) to electrophoresis (EP) mechanism. Charging of the water microdroplets through the Rayleigh jetting from electrified water/oil interface is suggested as the cause of the DEP-EP transition. Fitting the kinetic data of the microdroplets to the models describing the motion of the microdroplets under the photovoltaic field yields the charging amount depending on the substrate configuration (∼1.7 × 10−11 and 3.9 × 10−12 C on the naked and PTFE-coated LN:Fe substrates), and also reveals the dominance of the EP mechanism in the co-existence of the DEP and EP mechanisms. The outcome of this paper will be quite important to the practicalization of the photovoltaic manipulation in LN-based optofluidic chips.

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Organic single crystals are attracting enormous attention and playing an indispensable role in the realization of high-performance electronic devices. In this paper, we reported an in-situ growth method for two-dimensional branch-like and hexagonal shapes fluoranthene crystals under the photophoretic and dielectrophoretic forces generated by the photothermal and photovoltaic effects in both vapor- and liquid- environments. The crystals grown via this method are characterized by the real-time controllability and large size. At the same time, the crystal morphology can also be modified through non-contact illumination. This growth method may serve the future demand for the crystal growth in different phases.

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