Surface Nanobubbles

James R. T. Seddon

“Nanobubble”• Height approx. 20-50nm• Width approx. 50-200nm

“Micropancake”• Height approx. 1-2nm• Width approx. 1-3μm

NOTE: These are not results of hydrophobicity

0nm

5nm

An immersed surface, at the nanoscale

Why are nanobubbles interesting?

Fundamental Interest:• Complete bulk diffusion should take place in microseconds.• Nanobubbles last for at least 10-11 orders of magnitude longer

than this!• Understanding surface wetting?• As a precursor to several catalytic reactions?• As a precursor to boiling?

Possible applications:• Controlling slip in microfluidic devices?

A possible explanation

“Superstability”

Patterning(?) substrates

Clearly we need to understand creation mechanisms for nanobubbles

Alcohol-water exchange

Liquid heating

Liquid heating(1K/min for 15 minutes,

from 25°C to 40°C)

Oversaturation through rapid heating

Nanobubbles form when the system is oversaturated with gas...

...but, all the studies in the literature vary gas and temperature. Can we distinguish between

the two effects?

Experiments

We will control the system during deposition of the liquid on the substrate.

1.Hold the substrate at 25°C; vary the liquid temperature; ensure the liquid is 100% saturated with air.

2.Hold the substrate at 25°C; vary the concentration of saturated air in the liquid; ensure the liquid is held at 30°C.

Substrate

1μm

• PFDTS-coated Si substrate – isotropic roughness (rms=0.4nm) – hydrophobic (θ≈110°)

Experimental system

• Water is Millipore purified.• Gas concentration measured with an oximeter.• Water temperature controlled/measured.• Substrate is at 298K during deposition.

Results 1: Effect of temperature(100.0% ± 0.2% gas saturation)

Results 2: Effect of gas concentration (30.0°C ± 0.2°C liquid temperature)

Conclusions

• Liquid temperature and gas concentration both play important roles in nanobubble formation.

• A very small zone exists in phase space, where nanobubbles preferentially form.

Acknowledgements

University of TwenteSezer CaynakStefan KooijHarold ZandvlietBene PoelsemaDetlef Lohse

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