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Liquid Contact Angle Measurement

Water contact angle measurements using micro-litre or pico-litre droplets inform on sample hydrophobicity

Contact Angle Measurement at a glance

When a liquid drop is placed onto a solid surface, the contact angle is the angle formed at the three-phase interface between the solid, liquid and gas phases. Measuring this angle allows quantification of the wettability (how a liquid spreads) of a surface or material, and therefore an investigation into the energetics of that interface.

Applications of Contact Angle Measurement

• Surface free energy measurement.
• Polar and dispersive component determination.
• Lewis acid and base component determination.
• Hydrogen bond force measurement
• Interfacial and surface tension analysis of liquids  

How does Contact Angle Measurement Work?

A contact angle is dependent upon the physicochemical properties of the solid surface and the liquid dropped onto that surface. Specifically it is the attractive and repulsive forces between these media, and the three phase interface properties of the interaction (gas, liquid and solid). Those interactions are broadly described by the prevalent adhesive and cohesive intermolecular forces. Cohesive forces between ‘similar’ molecules such as those of the liquid molecules (i.e. hydrogen bonds and Van der Waals forces) balance against the adhesive forces between ‘dissimilar’ molecules such as those between the liquid and solid molecules (i.e. mechanical and electrostatic forces). This balance will determine the contact angle.

A large contact angle suggests that cohesive forces are stronger in ratio than adhesive forces, and the molecules of the liquid interact to a greater extent with each other than with the solid molecules. Surface wettability is low, and spreading of the drop is minimal and/or slow. However, a small contact angle represents cohesive forces being weaker in ratio to adhesive forces, and molecules of the liquid interacting to a greater extent with the solid molecules than themselves, Surface wettability is high, and spreading of the drop in great and/or fast.

While several different systems can be employed to take a contact angle measurement (depending on the exact operational desire), the most simplistic is a sessile drop technique where a contact angle goniometer is employed with an optical subsystem to capture the profile of a pure liquid drop on a solid substrate. If the size of the drop is not altered during the measurement this is a ‘static’ measurement. Alternatively the drop can be increased and then decreased in size with an advancing and receding contact angle in a ‘dynamic’ measurement. The angle formed between the liquid/solid interface and the liquid/vapour interface is measured directly by observation. This value can then be used in thermodynamic equations to calculate such properties as surface energies and surface tensions.  

Our Contact Angle Facilities

Publications of Interest

• Upper critical solution temperature thermo-responsive polymer brushes and a mechanism for controlled cell attachment, Xue, X., Thiagarajan, L., Braim, S., Saunders, B. R., Shakesheff, K. M. & Alexander, C., Journal of Materials Chemistry B, 5, 4926–4933 (2017).
• Surface-controlled spatially heterogeneous physical properties of a supramolecular gel with homogeneous chemical composition, Yang, B., Lledos, M., Akhtar, R., Ciccone, G., Jiang, L., Russo, E., Rajput, S., Jin, C., Angelereou, M. G. F., Arnold, T., Rawle, J., Vassalli, M., Marlow, M., Adams, D. J. & Zelzer, M., Chemical Science,12, 14260–14269 (2021).