Contact angle hysteresis can give valuable information on the properties of your surfaces. One of the often-used measurement methods is called tilting cradle or plate. The droplet is placed on the sample after which the tilting of the sample is started. The measurement can be done either with the manual tilting stage where only the sample stage is tilted or with the automated tilting cradle where the whole instrument is tilted.
Automation for better repeatability and ease-of-use
The one benefit of automated tilting cradle is that the tilting can be done with constant inclination speed that is defined in the software. With the manual tilting stage, the speed of inclination is dependent on the user which can make it difficult to compare results between different users. With the automated method, the tilting angle is also recorded by the software which makes the determination of roll-off or sliding angle easier. Also, the placement of the drop is not that critical as the whole instrument is tilted. With the tilting stage, the drop needs to be placed on the center of the image to ensure that the droplet is visible through the whole tilting range.
Volume of the drop influences the results
As the method is based on gravity, the volume of the droplet used is meaningful. The bigger the drop, the larger the gravity affected by the drop. It is thus important to use the same drop size if the results are being compared with each other. Typically, at least 10 µl drops are used. The roll-off or sliding angle is especially sensitive to the size of the droplet used.
To see how the measurements can be done in practice, please watch the video through the link below.
The measurement methods can be divided into optical (needle and tilting methods) and force (Wilhelmy method) depending on the measurement principle used. All the methods are measuring advancing and receding contact angles which are used to calculate contact angle hysteresis.
Contact angle hysteresis (CAH) is an important physical phenomenon. When you look through the window on a rainy day, you have probably noticed that some of the water droplets stick to the glass even though gravity is pulling them down. The phenomenon can be explained by contact angle hysteresis.
Contact angles are routinely measured as they offer simple, yet extremely sensitive measurement method for surface characterization. Although, the static contact angle is an excellent tool, more in-depth understanding of the surface properties require dynamic contact angle measurements.