Contents

Roll off / sliding angle

Pronunciation: /rəʊl ɒf ˈslaɪdɪŋ ˈæŋɡəl/

The roll off angle, or sliding angle, is the smallest tilt of a surface at which a drop of a given volume starts to move. It shows how easily drops leave a surface, which a static contact angle does not.

Also called

Sliding angle Roll off angle

Related terms

Tilting plate Hydrophobic vs hydrophilic Lotus effect

Topics

Sliding angle Wetting
Book a 15 minute demo Read the sliding angle measurement guide

At a glance

What the roll off angle tells you.

Typical values

Reported in degrees, with the drop volume. Superhydrophobic, self cleaning surfaces are commonly described as having a water contact angle above 150° and a sliding angle below 10°.

Related terms

Nearby wetting terms.

Related terms

  • Tilting plate
  • Contact angle hysteresis
  • Lotus effect

FAQ

Common questions.

Is a high contact angle the same as a low roll off angle?

No. Contact angle shows repellency; roll off angle shows mobility. A rough surface can show both a high angle and strong pinning. Students test both in experiment 8 on sliding and roll off angle, and the measurement method selector suggests which test to run.

What controls the roll off angle?

Mainly contact angle hysteresis and drop size. Hysteresis sets how strongly the drop is pinned. Teaching labs can compare tilting setups in our guide to the best contact angle goniometer for teaching and academic labs.

References

Primary sources.

1. Furmidge, C. G. L. (1962). Studies at phase interfaces. I. The sliding of liquid drops on solid surfaces and a theory for spray retention. Journal of Colloid Science, 17(4), 309 to 324. https://doi.org/10.1016/0095-8522(62)90011-9
2. Pierce, E., Carmona, F. J., and Amirfazli, A. (2008). Understanding of sliding and contact angle results in tilted plate experiments. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 323(1 to 3), 73 to 82. https://doi.org/10.1016/j.colsurfa.2007.09.032
3. ISO 19403-7:2024. Paints and varnishes. Wettability. Part 7: Measurement of the dynamic contact angles and the roll-off angle on a tilt stage. International Organization for Standardization. https://www.iso.org/standard/87267.html
4. Sliding angle measurement guide
5. Tilting plate
6. Lotus effect