# Understanding how plasma interacts with water for cleaner technologies

**Source**: https://www.tue.nl/en/news-and-events/news-overview/18-03-2026-understanding-how-plasma-interacts-with-water-for-cleaner-technologies
**Parent**: https://www.tue.nl/en/research

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# Understanding how plasma interacts with water for cleaner technologies

March 18, 2026

Olivier van Rooij defended his PhD thesis at the Department of Applied Physics and Science Education on March 17.

Olivier van Rooij.

**Olivier van Rooij** has investigated one of the most fundamental yet least understood processes in plasma science: the interaction between a **plasma discharge and a water surface**. His research provides new insights into how plasma-treated water (PTW) acquires disinfecting and nutrient-rich properties, helping unlock applications in **biomedicine, agriculture, and sustainable chemistry**.

### **What happens when plasma touches water?**

When a sharp electrode above water is energized with a high voltage, a plasma forms and propagates toward the water surface. The energetic electrons and reactive species created in this gaseous breakdown trigger rapid chemical reactions in the thin surface layer of the water. Only **long-lived species** make it into the bulk liquid, most importantly:

- **Nitrate (NO****₃⁻****)**
- **Nitrite (NO****₂⁻****)**
- **Hydrogen peroxide (H****₂****O****₂****)**

These species give plasma-treated water both **disinfecting properties** and **plant‑nutrient value**, explaining its growing relevance for medical sterilization and sustainable agriculture.

### **A water layer that changes during treatment**

A key finding of the thesis is that water is **not a passive target,** its electrical role changes during plasma exposure. At low conductivity, water behaves like a **dielectric barrier**, blocking current from reaching the submerged electrode and causing charge to accumulate on the surface. This prevents plasma from penetrating deeper, similar to a dielectric barrier discharge.

As the plasma creates more ions in the water, its conductivity rises. The water then behaves like a **high‑resistance conductor**, allowing electrolysis to occur and enabling plasma to form a continuous conducting path. These two regimes, dielectric and electrolytic, coexist and change dynamically during treatment.

Olivier van Rooij's thesis cover

### **Measuring nanosecond plasma dynamics**

To understand this evolving system, Van Rooij employed a suite of diagnostics to track both plasma and water properties:

- **iCCD imaging** to capture plasma morphology on **nanosecond timescales**
- **Electrical measurements** to determine energy dissipation, charge deposition, and discharge regime
- **Optical emission spectroscopy** to extract **gas temperature** and **electron density**, the latter reaching ~10²¹ m⁻³ based on Stark broadening of hydrogen lines
- **pH and conductivity measurements** to infer concentrations of NOₓ⁻ species in the water

Together, these tools reveal how changes in the water feed back into plasma formation and vice versa, showing a tightly coupled, evolving system rather than a one‑way interaction.

### **How pulse parameters control plasma-water chemistry**

Van Rooij also studied how different electrical driving conditions influence the plasma-water interaction. Using a **custom‑designed pulse generator**, he independently varied rise time, pulse length, frequency, and waveform shape. These experiments show that pulse parameters have a **strong effect on species generation, discharge morphology, and the transition between dielectric and electrolytic behavior**. This knowledge allows future plasma devices to be tuned for specific outcomes, whether maximizing disinfecting power, optimizing fertilizer production, or ensuring gentle biomedical treatment.

### **Toward controlled and application-ready plasma-treated water**

By revealing how water conductivity, humidity, plasma parameters, and charge dynamics all shape the chemistry of plasma-treated water, this thesis provides a scientific basis for better control of PTW generation. Van Rooij’s work strengthens the foundation for technologies ranging from **environmentally friendly agriculture** to **cold plasma medicine**, where controlling reactive species in water is essential for safe and effective use.

- [### PhD student

  Olivier van Rooij, Department of Applied Physics and Science Education

  Read more](https://research.tue.nl/nl/persons/olivier-jap-van-rooij/)
- [### Dissertation title

  The interplay between plasma and a water interface dissertation

  Read more](https://pure.tue.nl/ws/files/380686227/20260317_Rooij_van_hf.pdf)
- ### Supervisors

  Ana Sobota & Gerrit Kroesen

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[l.m.walrecht@tue.nl](#)