Abstract
An accurate description of contact angle hysteresis in AC electrowetting is important for a wide range of practical electrowetting applications. This work demonstrates that electrowetting actuated advancing contact angles and the reduction of contact angle hysteresis in AC electrowetting are better predicted when characterizing the advancing electrowetting force by its root mean square (rms) value as opposed to its time-averaged or maximum values. Characterizing the electrowetting force by its rms value allows the transient electrowetting force to exceed the pinning force for some amount of time overcoming the inertial effects at the contact line before advancement. This is opposed to the maximum force characterization which implies that inertial effects can be neglected at the contact line resulting in immediate advancement when the forces are unbalanced.
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Data availability statement
The datasets generated during and/or analyzed during the current study are available from the corresponding author on reasonable request.
Abbreviations
- \(a\) :
-
Subscript denoting a property when the contact line is advancing
- \({\text{avg}}\) :
-
The time-averaged value of a transient variable. Superscript/subscript denoting the time-averaged value
- \(c\) :
-
Capacitance per unit area of the solid–liquid interface on an electrowetting on dielectric device
- \({\text{crit}}\) :
-
Subscript denoting a property associated with the critical Electrowetting number where contact angle hysteresis is predicted to be eliminated
- Ew:
-
Electrowetting number, a ratio of electrical and interfacial energy at the solid–liquid interface and subscript denoting a property under that electrowetting number. Superscript and subscript denoting properties (e.g., contact angle) under electrowetting actuation
- \(f^{\prime}\) :
-
Force per unit length at the contact line (in the units of surface tension)
- \(f\) :
-
Dimensionless force at the contact line
- \({\text{int}}\) :
-
Superscript denoting the case where the electrowetting number is such that the cosine of the advancing and receding contact angles both intersect with the electrowetting equation
- \({\text{LM}}\) :
-
Subscript denoting a property associated with the interface between the liquid droplet and surrounding medium
- \({\text{max}}\) :
-
The maximum value of a transient variable. Superscript/subscript denoting the maximum value
- \({\text{min}}\) :
-
The minimum value of a transient variable. Superscript/subscript denoting the minimum value
- \(p\) :
-
Subscript denoting pinning force
- \(pk\) :
-
Superscript denoting peak voltage
- \(r\) :
-
Subscript denoting a property when the contact line is receding
- \({\text{rms}}\) :
-
Subscript denoting the root mean square average of a transient variable
- \({\text{SL}}\) :
-
Subscript denoting a property associated with the interface between the solid and the liquid droplet
- \({\text{SM}}\) :
-
Subscript denoting a property associated with the interface between the solid and the surrounding medium
- \(t\) :
-
Time
- \(U\) :
-
Voltage
- \(Y\) :
-
Superscript denoting the equilibrium contact angle suggested by Young’s equation
- \(\alpha\) :
-
Constant found to scale dimensionless pinning force to electrowetting number for pinning forces under various contact line pinning models
- \(\gamma\) :
-
Surface tension between any two phases in the system
- \(\theta\) :
-
Contact angle
- \(\omega\) :
-
Actuation frequency of an electrical voltage
- \(0\) :
-
Subscript denoting the unactuated condition (i.e., \(Ew = 0\))
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Acknowledgements
We gratefully acknowledge support from ADVANCE RIT (funded through the National Science Foundation under Award No. HRD-1209115) and the Kate Gleason College of Engineering at RIT.
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Partial financial support was received from ADVANCE RIT (funded through the National Science Foundation under Award No. HRD-1209115) and the Kate Gleason College of Engineering at RIT.
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The authors have no relevant financial conflicts of interests to disclose. Dr. Schertzer’s research group received funding from an industrial partner to work on a project where the industrial partner was also working with Associate Editor Dr. Hywel Morgan. However, Dr. Schertzer and Dr. Morgan never directly collaborated on interacted on the project.
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Bernetski, K.A., An, H.T., Maki, K.L. et al. Predicting actuated contact line pinning forces and the elimination of hysteresis under AC electrowetting. Microfluid Nanofluid 26, 94 (2022). https://doi.org/10.1007/s10404-022-02599-z
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DOI: https://doi.org/10.1007/s10404-022-02599-z