Water Contact Angle

Water Contact Angle (WCA)

Water contact angle is indicative of wettability, hydrophobicity, and the strength of contact in a solid-liquid interaction.

It is as straightforward a technique as its name implies. A drop of water is cast on the surface of a solid. Then, the angle between the face of the solid surface (0 degrees), and the tangent line to the contacting edge of the droplet is measured using a precision goniometer. Goniometers are, fundamentally, optical imaging systems that film the behavior of a droplet from when it lands on a substrate and to the start of its spread or relaxation on the surface. Contact angle is measured over time during this relaxation process, and the Young-Dupre Equation is used to determine the wettability and interaction strength at the solid-liquid interface.

If the angle is greater than 90 degrees, the affinity between the solid and liquid is very low. If the droplet is water, then the material is considered to be hydrophobic. As the angle becomes more acute, the wettability and hydrophilicity of the material proportionately increase.

How contact angle (theta) is measured on a standard droplet (red). From Ossila.

Application Areas for WCA

Water contact angle can be quickly and easily measured to characterize hydrophobic and hydrophilic materials, and can imply insights into surface porosity, roughness, and heterogeneity. This technique is readily utilized in biochemistry, organic chemistry, polymers science, thin film analysis, coating development, textiles and fabric production, as well as in solvent design, cleaning process evaluation, industrial and mechanical engineering, plumbing systems manufacturing, as well as a host of other fields.

Particularly relevant to contemporary concerns: water contact angle can be used in biomedical and public health applications to evaluate the susceptibility of surfaces to respiratory droplets.

Measurements from WCA

  • Wettability and liquid affinity
  • Surface tension
  • Hydrophobicity

Uses and Limitations for WCA

  • What it is great for:
    • Quick, straightforward measurement of liquid-solid interface
    • Indirect measurement of surface free energy
  • Limitations:
    • Expertise required to make accurate measurements

Sample Output

Water Contact Angle measuremenon PEDOT:PSS showing high hydrophilicity in the substrate.
From Ossila.

Contact Angle measurement of glycerol droplet over 4 seconds, showing relaxation behavior indicative of high surface wettability.
From Ossila.

INSTRUMENTS we use for WCA

Ossila Contact Angle Goniometer

The Ossila Contact Angle goniometer provids quick, precise, and reliable contact angle measurement to assay surface tensions of liquid droplets. It can achieve a measurement accuracy within 1 degree, and is capable of capturing time-dependent WCA measurements.