Visible-light-assisted condensation of ultrasonically atomized water vapor on LiNbO₃:Fe crystals

Optically massive trapping of the moisture in the air into an adjacent surface is a potential technique in the fields of bacterial adhesion and microfluidic generation, which is quite important to the development of LN-based biological lab-on-chips. Here we demonstrate on a LiNbO₃:Fe substrate the visible-light-assisted condensation of the water vapor in a flowing stream created by an ultrasonic atomizer. Through analyzing the dynamic processes of the visible-light-assisted water condensation at different illumination intensities, it is found that the extent of the water condensation, the bending angle of water vapor trails and the interaction range of the condensation effect are highly dependent on the illumination intensity. According to these findings and the simulated trajectories of the water vapor stream at different illumination intensities, we propose that this visible-light-assisted water condensation is an aggregation process of tiny water droplets driven by the dielectrophoretic interaction of inhomogeneous photovoltaic field and also an electrostatic screening course of photovoltaic charges through the charged evaporation of condensed water. The prolonged condensation of water vapor after a high-intensity illumination and that of oil vapor at a super-low evaporation rate are also studied, and the agreement between the simulation and experimental results reinforces the above mechanism. The reported technique, employing the inexpensive, safe-for-cell visible laser beam, is quite convenient for the controllable generation of various biological microdroplets, and thus it is promising for the microfluidic functionality integration of LN-based biological lab-on-chips.