Application Cases

Experiment Name: Experimental Study on Wetting State Transition and Its Impact on Lubrication Performance

Test Purpose: This section mainly focuses on the selection and preparation of experimental materials and the establishment of an experimental platform for electrowetting experiments. First, the selection and preparation methods of various experimental materials are introduced. Next, the contact angle and roll-off angle of deionized water on different structured surfaces after hydrophobic treatment are measured. Finally, the changes in contact angle and filling state of the liquid droplet under electric and non-electric conditions are measured, and the patterns are studied.

Testing Equipment: Voltage amplifier, signal generator, contact angle meter, etc.

Experimental Process:

Figure 1: Electrowetting Experimental Setup

Before the experiment, the preparation of electrowetting test samples, dielectric layer, and hydrophobic layers is carried out. Then, an electrowetting experimental platform as shown in Figure 1 is set up. The experimental power supply uses a combination of a signal generator and a voltage amplifier. A contact angle meter is used to measure the contact angle of water (5μl) under electric and non-electric conditions. The changes in the state and filling condition of the liquid droplet are observed, and the changes in the roll-off angle under electric and non-electric conditions are measured using the contact angle meter.

Experimental Results:

Figure 2: Liquid Droplet State on Electrowetting Rough Surface

One significant feature of the experimental process is the direct visual observation of the liquid droplet state transition induced by electrowetting. Figure 2 shows the liquid droplet on an electrowetting surface with roughness φ=0.18, rm=2.25, and h=60μm. On the left, the liquid droplet is clearly in the Cassie state without applied voltage, as the background light between the pillars is clearly visible. The existence of the Cassie state can be confirmed by directly observing the visibility of light between the pillars, which is similar to the experimental determination of the Cassie state. The white area in the center of the droplet is caused by the backlight optical effect. On the right, the liquid droplet transitions to the Wenzel state when a voltage of 130V is applied. The voltage is applied through a wire that contacts the top of the droplet. Since no background light passes between the pillars and is instead filled by the droplet, it can be confirmed that the droplet is in the Wenzel state.

Figure 3: Initial State of Droplets on Different Pillar Heights (Left: Low Micron Pillars; Right: Nanometer Pillars)

The method of direct visual observation to determine the onset of droplet transition is used in all experiments in this paper. However, for microstructures with low pillar heights or high φ values, direct visual observation is not applicable (as shown in Figures 4-9), because in the Cassie state, high-density pillars significantly reduce the light pathway in the available area, making it impossible to directly visually observe the initial state.

Recommended Voltage Amplifier: ATA-2082

Figure: ATA-2082 High-Voltage Amplifier Specifications

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