Part 3 of a Chromis Technologies series on using AFPs for precise surface control
Introduction
The ability to move droplets without pumps or valves might sound like science fiction – but it’s already transforming diagnostics, displays, and environmental sensing. At the heart of this transformation is electrowetting-on-dielectric (EWOD), a technique that uses electric fields to precisely control liquid motion on solid surfaces. At the core of EWOD systems are specialized dielectric and hydrophobic layers – materials that must balance electrical insulation and chemical stability with precise surface control.
This is the third article in our series on amorphous fluoropolymers (AFPs) and their role in next-generation surface engineering. In Part 1, we introduced the core properties of AFPs. In Part 2, we explored how these materials enable tunable surface energy and wettability.
Now, we turn to EWOD and how AFPs make this digital fluid control possible, reliable, and scalable.
EWOD Technology
Fundamental Principles
EWOD is a foundational technology that enables precise control over liquid droplets by applying an electric field to a hydrophobic surface. When a voltage is applied between a conductive droplet and an electrode beneath a dielectric layer, the droplet’s contact angle changes – causing it to move, spread, or contract (Verheijen & Prins, 1999; Wu et al., 2020). This contact angle modulation, driven by the interplay of electrostatic force and surface tension, makes EWOD a powerful method for dynamic liquid manipulation. The starting angle – known as the electrowetting contact angle (θ0) – is influenced by surface tension and the properties of the dielectric material (Wu et al, 2020; Li, 2007). These principles underpin several emerging technologies, many of which benefit from the unique capabilities of AFPs.
Historical Development
The core principle behind electrowetting, known as electrocapillarity, was first described by Gabriel Lippmann in 1875. His experiments showed that an applied voltage could influence liquid behavior in capillary systems – an insight that laid theElectrowetting.org theoretical foundation for modern EWOD. The term electrowetting itself was introduced in 1981 by G. Beni and S. Hackwood during their work on electrically responsive display devices (Beni & Hackwood, 1981). In the 1990s, Bruno Berge and colleagues significantly advanced the field by adding an insulating dielectric layer between the droplet and the electrode. This innovation improved stability and expanded electrowetting’s potential for practical applications (Electrowetting.org, n.d.).
Dynamic Surface Control and Emerging Applications
At its core, EWOD provides a precise way to dynamically modify surface wettability – without mechanical components. As voltage increases, the contact angle decreases, allowing greater control over fluid motion (Wu et al., 2020). This principle is behind a growing number of technologies, from tunable optics to next-generation display systems. One of the most promising frontiers is digital microfluidics – a field powered by digital microfluidic chips and biochips that use EWOD to manipulate tiny volumes of liquid with speed and precision. While we won’t explore those systems in depth here, AFP-enabled EWOD platforms are fast becoming the bedrock of many cutting-edge digital microfluidics applications. A closer look at this rapidly evolving domain is the focus of the next article in this series.
Properties of Amorphous Fluoropolymers
AFPs possess a blend of properties that make them nearly tailor-made for EWOD systems and digital microfluidic devices. Their non-crystalline molecular structure gives them unique advantages in performance, processing, and reliability – particularly in applications that require precise droplet control, high electrical insulation, and chemical durability.
Extreme Hydrophobicity and Oleophobicity
A key principle of electrowetting is the ability to modulate the contact angle of a droplet. AFPs naturally exhibit extremely low surface energy, making them both hydrophobic (water-repellent) and oleophobic (oil-repellent). This allows droplets to form well-defined spherical shapes – or “bead up” – on the surface, a condition essential for initiating effective droplet movement. The low surface friction also facilitates smooth transport during EWOD actuation, reducing energy loss and improving response times.
Excellent Dielectric Properties
In EWOD systems, the dielectric layer must electrically isolate the droplet from the actuation electrodes while still allowing the electric field to influence surface tension. AFPs serve this role exceptionally well. They offer:
- High dielectric strength, enabling them to withstand the applied voltages without electrical breakdown.
- Low dielectric constant, which minimizes parasitic capacitance and improves control efficiency in digital microfluidics electrowetting operations.
These electrical characteristics are fundamental to stable, low-voltage actuation across a wide range of digital microfluidic chips.
Optical Transparency
Many AFPs are optically transparent across a wide spectral range – from deep ultraviolet (DUV) through visible light to near-infrared (NIR) wavelengths (Yang et al., 2018). This transparency is essential in digital microfluidics for biological analysis and applications, where optical detection methods such as fluorescence and absorbance are often integrated into the chip. The use of AFPs allows for real-time monitoring without interfering with signal quality.
Chemical Inertness and Biocompatibility
In microfluidic environments, materials often come into contact with reactive chemicals or biological reagents. AFPs are highly chemically inert and biocompatible, offering resistance to acids, bases, solvents, and biological contamination. These properties help maintain sample integrity and extend the functional life of EWOD devices – particularly important in digital microfluidic biochips used for clinical diagnostics or pharmaceutical research.
Solution Processability
Unlike semi-crystalline fluoropolymers such as PTFE, which require high-temperature processing, AFPs are typically solution-processable. They can be spin- and dip-coated, spray-deposited, or even inkjet-printed from specialized fluorinated solvents. This ease of processing allows for the formation of thin, uniform, and patterned dielectric layers on EWOD substrates – simplifying the fabrication of digital microfluidics platforms.
Low Contact Angle Hysteresis
Contact angle hysteresis – the difference between advancing and receding contact angles – can significantly impact droplet motion. High hysteresis leads to “sticking” or unpredictable behavior, undermining the reliability of droplet control. AFPs generally exhibit very low contact angle hysteresis, enabling consistent and repeatable droplet manipulation in EWOD systems, even over extended use.
Applications of Amorphous Fluoropolymers in Electrowetting
AFPs have become critical enablers of electrowetting-on-dielectric (EWOD) systems because of the unique combination of properties described above. These materials improve the responsiveness and reliability of electrowetting devices, helping reduce actuation voltages, enhance droplet manipulation, and support long-term durability. Their integration has made EWOD technology scalable and practical for a wide range of applications – many of which are now central to the growth of digital microfluidics.
Digital Microfluidics and Bioanalysis
AFPs are foundational to the performance of digital microfluidic chips used in lab-on-a-chip systems, biomedical diagnostics, and chemical processing. In these platforms, EWOD is used to manipulate microliter-scale droplets – transporting, merging, and splitting them with precision. AFP-coated surfaces ensure chemical compatibility and reduce contamination, which is vital in sensitive procedures like digital microfluidics PCR or magnetic digital microfluidics. Their low surface energy minimizes droplet pinning, supporting more accurate and reliable fluid handling. While we’ll explore digital microfluidic biochips and related technologies in the next article, it’s worth noting that AFPs play a central role in enabling these systems to operate at low voltages with high consistency.
Display Technologies
Electrowetting displays (EWDs) are another major application of AFP-enabled EWOD systems. These displays use electric fields to reposition colored oil droplets on a hydrophobic insulating layer, creating sharp, reflective images. AFPs improve EWD performance by delivering fast switching speeds, low-voltage operation, and stable surface characteristics. The result is a lightweight, low-power alternative to traditional LCDs – particularly well-suited for mobile, wearable, and e-paper devices.
Environmental Monitoring and Management
EWOD technology, when combined with the durability and chemical resistance of AFPs, is showing increasing promise in environmental monitoring and remediation.
In water quality applications, EWOD platforms can assist in detecting heavy metals, nutrients, pathogens, and toxins by enabling precise droplet mixing and controlled micro-reactions. Similarly, AFP-coated surfaces can support air-quality systems by helping capture or manipulate particulates or bioaerosols at microscale levels. These emerging uses point to a future where EWOD-based devices may play a role in safeguarding environmental health.
On the remediation side, EWOD’s fine droplet control opens possibilities for separating oil from water, concentrating contaminants, or supporting controlled reactions that break down pollutants. The chemical inertness of AFPs ensures that such systems can handle corrosive materials without degrading performance.
While many of these applications will rely on integrated digital microfluidic devices, the enabling technologies – including AFP coatings and EWOD actuation layers – are already being engineered today. A deeper look into those systems will be the focus of the next article in this series.
Challenges and Future Directions
Despite their advantages, AFPs and EWOD systems face several technical hurdles, including:
- Surface morphology degradation from repeated droplet impacts, which can increase contact angle hysteresis and reduce device reliability (Wu, 2020)
- Increased actuation voltage requirements associated with thicker, more durable hydrophobic coatings (Wu, 2020)
- Charge trapping and chemical degradation of fluoropolymer surfaces over time, which can compromise dielectric stability and long-term performance (Wu, 2020; Krishnan et al., 2023)
These issues can limit practical deployment, particularly in advanced applications such as digital microfluidics SPR (surface plasmon resonance) and emerging 5G-compatible sensing platforms (Krishnan et al., 2023).
Looking ahead, continued innovation in AFP synthesis and solution-processable coating technologies is expected to improve material performance while lowering cost and environmental impact. As digital microfluidics companies push the frontiers of lab automation, diagnostics, and miniaturized chemical analysis, AFPs are poised to remain a core enabler of scalable, high-precision EWOD systems.
Conclusion
Electrowetting-on-dielectric technology has matured into a versatile platform for precise droplet manipulation, enabling a new generation of microfluidic and display systems. At the heart of many of these innovations are amorphous fluoropolymers – materials whose exceptional dielectric strength, hydrophobicity, chemical resistance, and optical transparency make them uniquely suited for EWOD applications.
As digital microfluidics continues to push into new domains – clinical diagnostics, environmental monitoring, soft electronics – the performance demands on electrowetting systems will only grow. AFPs, with their balance of functional and processable properties, are poised to meet these challenges head-on. While technical hurdles remain, ongoing advances in AFP material science and coating techniques promise to expand what EWOD systems can do.
Next Steps in the Series
The next article in this series will take a deeper look at digital microfluidics technology and the applications it enables.
Learn More
Interested in how amorphous fluoropolymers can advance your cutting-edge research or new product development? Our team at Chromis Technologies is here to help.
Contact us to learn more about our materials, capabilities, and how we can support your innovation initiatives.
References
Verheijen, H. J. J., & Prins, M. W. J. (1999). Reversible electrowetting and trapping of charge: Model and experiments. Langmuir, 15(20), 6616–6620. https://doi.org/10.1021/la990548n
Wu, H., Dey, R., Siretanu, I., van den Ende, D., Shui, L., Zhou, G., & Mugele, F. (2020). Electrically controlled localized charge trapping at amorphous fluoropolymer–electrolyte interfaces. Small, 16(2), e1905726. https://doi.org/10.1002/smll.201905726
Wu, H. (2020). Electrically responsive fluoropolymer surfaces and applications (Doctoral dissertation, University of Twente). https://doi.org/10.3990/1.9789036549523
Li, Y. (2007). Surface engineering of electrowetting-on-dielectric (EWOD) for microfluidics (Unpublished doctoral dissertation). The University of Edinburgh.
Lippmann, G. (1875). Relation entre les phénomènes électriques et capillaires. Annales de Chimie et de Physique, 5(11), 494–549.
Beni, G., & Hackwood, S. (1981). Electrowetting displays. Applied Physics Letters, 38(4), 207–209. https://doi.org/10.1063/1.92322
Electrowetting.org. (n.d.). History of electrowetting. Retrieved July 25, 2025, from https://electrowetting.org/?p=history
Yang, T., Choo, J., Stavrakis, S., & de Mello, A. (2018). Fluoropolymer-coated PDMS microfluidic devices for application in organic synthesis. Chemistry – A European Journal, 24(46), 12078–12083. https://doi.org/10.1002/chem.201802750
Krishnan, S. G., Jaishankar, A., & Tserepi, A. (2023). Challenges in electrowetting-on-dielectric devices and potential solutions. Micro and Nano Systems Letters, 11(1), 8. https://doi.org/10.1186/s40486-023-00197-4
Other Sources
Son, Y., Kim, W., Lee, D., & Chung, S. K. (2024). Study on repetitive damage-recovery cycle of hydrophobic coating for electrowetting-on-dielectric (EWOD) applications. Micro and Nano Systems Letters, 12, 4. https://doi.org/10.1186/s40486-023-00197-4
Krupenkin, T., Yang, S., & Mach, P. (2003). Tunable liquid microlens. Applied Physics Letters, 82(3), 316–318. https://doi.org/10.1063/1.1536033
Papageorgiou, D. P., Tserepi, A., Boudouvis, A. G., & Papathanasiou, A. G. (2012). Superior performance of multilayered fluoropolymer films in low voltage electrowetting. Journal of Colloid and Interface Science, 368(1), 592–598. https://doi.org/10.1016/j.jcis.2011.10.035
Seyrat, E., & Hayes, R.A. (2001). Amorphous fluoropolymers as insulators for reversible low-voltage electrowetting. Journal of Applied Physics, 90, 1383-1386. https://doi.org/10.1063/1.1383583
Yue, R.-F., Wu, J.-G., Zeng, X.-F., Kang, M., & Liu, L.-T. (2006). Demonstration of four fundamental operations of liquid droplets for digital microfluidic systems based on an electrowetting-on-dielectric actuator. Chinese Physics Letters, 23(8), 2303. https://doi.org/10.1088/0256-307X/23/8/093
Oishi, E., Araki, N., Goto, T., Awano, H., & Takahashi, T. (2019). The Effect of the Terminal Functional Groups on Fluoropolymer on Electrowetting Device Performance. Technologies, 7(3), 52. https://doi.org/10.3390/technologies7030052
Bezelya, A., Küçüktürkmen, B., & Bozkır, A. (2023). Microfluidic Devices for Precision Nanoparticle Production. Micro, 3(4), 822-866. https://doi.org/10.3390/micro3040058
Sun, Q., Wang, D., Li, Y. et al. Surface charge printing for programmed droplet transport. Nat. Mater. 18, 936–941 (2019). https://doi.org/10.1038/s41563-019-0440-2
Frequently Asked Questions (FAQs)
What is electrowetting-on-dielectric (EWOD)?
EWOD is a technique that uses an electric field to change the wetting properties of a surface, allowing droplets to move, split, or merge. A dielectric layer separates the droplet from the electrode, enabling precise control without direct electrical contact.
How are amorphous fluoropolymers (AFPs) different from other fluoropolymers?
AFPs are non-crystalline, meaning they lack an ordered molecular structure. This makes them more optically transparent and easier to process than semi-crystalline fluoropolymers like PTFE.
Why are AFPs ideal for EWOD applications?
AFPs combine extreme hydrophobicity, high dielectric strength, chemical inertness, and low contact angle hysteresis – key traits that support efficient, low-voltage, and long-lasting EWOD performance.
What are digital microfluidic devices?
Digital microfluidic devices manipulate discrete droplets of liquid on a flat surface using electrowetting. These systems are used in lab-on-a-chip platforms, diagnostics, drug discovery, and portable analytical tools.
What is contact angle hysteresis, and why does it matter?
When a droplet moves across a surface, the front edge pushes forward and the back edge pulls away. If the surface holds onto the droplet too tightly, it gets stuck or moves unevenly. That’s called contact angle hysteresis – it’s like friction for droplets. The smooth, water-repellent surfaces of amorphous fluoropolymers have very low contact angle hysteresis and let droplets glide more easily, without sticking. That’s why AFPs are so useful in EWOD and digital microfluidics, where precise and predictable droplet movement is key.
Are EWOD systems already used in real-world products?
Yes. Electrowetting displays (EWDs), some lab-on-a-chip diagnostic tools, and environmental sensors all use EWOD or closely related technologies. Integration is expected to increase as materials like AFPs improve device performance and manufacturability.
Can AFP-based EWOD systems be scaled for mass production?
Yes. Thanks to their solution processability, AFP coatings can be applied using industry-standard methods like spin coating or inkjet printing, making them viable for large-scale production of digital microfluidic chips.
What’s next for AFPs in electrowetting?
Future developments will focus on improving dielectric reliability, reducing actuation voltages, and expanding applications in areas like 5G-compatible sensors, surface plasmon resonance (SPR), and field-deployable diagnostics.