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AC Electrowetting Modulation of Low-Volatile Liquids Probed by XPS: Dipolar vs Ionic Screening
Langmuir ( IF 3.7 ) Pub Date : 2019-02-15 00:00:00 , DOI: 10.1021/acs.langmuir.8b04099 Pinar Aydogan Gokturk 1 , Burak Ulgut 1 , Sefik Suzer 1
Langmuir ( IF 3.7 ) Pub Date : 2019-02-15 00:00:00 , DOI: 10.1021/acs.langmuir.8b04099 Pinar Aydogan Gokturk 1 , Burak Ulgut 1 , Sefik Suzer 1
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X-ray photoelectron spectroscopic (XPS) data have been recorded for a low-molecular-weight poly(ethylene glycol) microliter-sized sessile liquid drops sitting on a dielectric covered planar electrode while imposing a ±6 V square-wave actuation with varying frequencies between 10–1 and 105 Hz to tap into the information derivable from (AC) electrowetting. We show that this time-varying XPS spectra reveal two distinct behaviors of the device under investigation, below and above a critical frequency, measured as ∼70 Hz for the liquid poly(ethylene glycol) with a 600 Da molecular weight. Below the critical frequency, the liquid complies faithfully to the applied bias, as determined by the constant shift in the binding energy position of the XPS peaks representative of the liquid throughout its entire surface. The liquid completely screens the applied electrical field and the entire potential drop takes place at the liquid/dielectric interface. However, for frequencies above the critical value, the resistive component of the system dominates, resulting in the formation of equipotential surface contours, which are derived from the differences in the positions of the twinned O 1s peaks under AC application. This critical frequency is independent of the size of the liquid drop, and the amplitude of the excitation, but increases when ionic moieties are introduced. The XP spectra under AC actuation is also faithfully simulated using an equivalent circuit model consisting of only resistors and capacitors and using an electrical circuit simulation software. Moreover, a mimicking device is fabricated and its XP spectra are recorded using the Sn 3d peaks of the solder joints at different points on the circuit to confirm the reliability of the measured and simulated AC behaviors of the liquid. These new findings indicate that in contrast to direct current case, XPS measurements under variable frequency AC actuation reveal (through differences in the frequency response) information related to the chemical makeup of the liquid(s) and brings the laboratory-based XPS as a powerful complimentary arsenal to electrochemical analyses of liquids and their interfaces.
中文翻译：
XPS探测的低挥发性液体的交流电润湿调制：偶极与离子筛选
X射线光电子能谱（XPS）数据已记录，它是低分子量聚（乙二醇）微升大小的固着液滴，它坐在电介质覆盖的平面电极上，同时施加±6 V方波驱动，频率变化在10 –1到10 5之间Hz以利用可从（AC）电润湿获得的信息。我们表明，该随时间变化的XPS光谱揭示了所研究设备的两种不同行为，在临界频率以下和以上，该临界频率在分子量为600 Da的液态聚乙二醇中约为70 Hz。在临界频率以下，液体忠实地遵守所施加的偏压，这由代表整个液体整个表面的XPS峰的结合能位置的恒定偏移确定。液体完全屏蔽了施加的电场，整个电位降发生在液体/介电界面。但是，对于高于临界值的频率，系统的电阻分量起主导作用，导致形成等势面轮廓，这是由于在交流电条件下孪生的O 1s峰的位置不同而引起的。该临界频率与液滴的大小和激发的幅度无关，但是当引入离子部分时会增加。使用仅由电阻器和电容器组成的等效电路模型以及电路仿真软件，也可以忠实地模拟交流驱动下的XP频谱。此外，制造了一个模拟设备，并使用电路上不同点的焊点的Sn 3d峰记录了XP光谱，以确认所测量和模拟的液体AC行为的可靠性。这些新发现表明，与直接案例相比，
更新日期：2019-02-15
中文翻译：
XPS探测的低挥发性液体的交流电润湿调制：偶极与离子筛选
X射线光电子能谱（XPS）数据已记录，它是低分子量聚（乙二醇）微升大小的固着液滴，它坐在电介质覆盖的平面电极上，同时施加±6 V方波驱动，频率变化在10 –1到10 5之间Hz以利用可从（AC）电润湿获得的信息。我们表明，该随时间变化的XPS光谱揭示了所研究设备的两种不同行为，在临界频率以下和以上，该临界频率在分子量为600 Da的液态聚乙二醇中约为70 Hz。在临界频率以下，液体忠实地遵守所施加的偏压，这由代表整个液体整个表面的XPS峰的结合能位置的恒定偏移确定。液体完全屏蔽了施加的电场，整个电位降发生在液体/介电界面。但是，对于高于临界值的频率，系统的电阻分量起主导作用，导致形成等势面轮廓，这是由于在交流电条件下孪生的O 1s峰的位置不同而引起的。该临界频率与液滴的大小和激发的幅度无关，但是当引入离子部分时会增加。使用仅由电阻器和电容器组成的等效电路模型以及电路仿真软件，也可以忠实地模拟交流驱动下的XP频谱。此外，制造了一个模拟设备，并使用电路上不同点的焊点的Sn 3d峰记录了XP光谱，以确认所测量和模拟的液体AC行为的可靠性。这些新发现表明，与直接案例相比，
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