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Electrically Mediated Static Contact Angle and Hysteresis of Polyelectrolyte Solutions
Sumit Kumar1, Patrick Martin1, Gleb Vasilyev1
1NanoEngineering Group, Department of Mechanical Engineering, Technion - Israel Institute of Technology, Haifa 3200003, Israel.
Langmuir : the ACS Journal of Surfaces and Colloids
|July 26, 2023
Summary
This study explores electrowetting-on-dielectric (EWOD) behavior in poly(acrylic acid) (PAA) solutions. It reveals that droplet ionization and polymer conformation under electric fields control wetting properties, offering new manipulation methods for biological polymers.
Area of Science:
- Surface Science and Engineering
- Materials Science
- Physical Chemistry
Background:
- Electrowetting-on-dielectric (EWOD) is crucial for droplet manipulation in diverse applications.
- Current EWOD research predominantly uses aqueous electrolytes and ionic liquids.
- The electrowetting of polyelectrolyte solutions remains largely unexplored.
Purpose of the Study:
- To investigate the electrowetting behavior of weak polyelectrolyte solutions, specifically poly(acrylic acid) (PAA).
- To understand how solution pH influences the ionization and wetting characteristics of PAA droplets.
- To elucidate the role of polymer conformation and charge-connectivity in controlling electrowetting gain and hysteresis.
Main Methods:
- Experimental investigation of electrowetting in poly(acrylic acid) solutions.
- Control of PAA ionization by adjusting solution pH.
- Application of electric fields to observe changes in droplet wetting behavior and hysteresis.
Main Results:
- Distinct wetting behaviors were observed for weakly and fully charged PAA droplets, dependent on pH.
- Strongly ionized PAA droplets exhibited enhanced wetting compared to weakly charged droplets under an electric field.
- Fully ionized PAA droplets showed higher electrowetting hysteresis, potentially due to electric-field-induced alignment of polymer chains near the contact line.
Conclusions:
- Charge-connectivity and polyelectrolyte conformation significantly influence electrowetting gain and hysteresis.
- The study reveals a novel electrowetting mechanism for polyelectrolyte solutions.
- Findings may enable precise ordering and manipulation of biological polyelectrolytes like DNA and polypeptides.
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