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August
2024 |
The Spreading Coefficient and Contact Angle |
The spreading coefficient is a
quantitative measure that describes the tendency of a liquid to
spread across a solid or even another liquid surface. It is particularly
useful in understanding the wetting behavior of liquids on various
surfaces. The spreading coefficient,
Mathematically, the spreading coefficient
where:
The value of the spreading coefficient determines the wetting behavior as follows:
The relationship between the
spreading coefficient
γ where
θ
is the contact angle. If we substitute
γ Knowing both the contact angle and the spreading coefficient provides a more comprehensive understanding of the wetting behavior and surface interactions of a liquid on a solid. While contact angle provides a snapshot of the equilibrium state of a droplet on a surface, it doesn't directly quantify the energy changes involved. The spreading coefficient not only quantifies the tendency of a liquid to spread, but can also predict dynamic wetting behavior, such as how quickly a particular liquid will wet or dewet a particular surface. In short, while the equilibrium contact angle provides valuable feedback relative to basic wetting behavior, the spreading coefficient is capable of providing a more expansive view of wetting dynamics by taking into account not only the contact angle but also the surface tension of the liquid. In practical terms, the spreading coefficient is crucial in applications where the control of wetting properties is important, such as in coatings, adhesives, lubrication, and the development of superhydrophobic and superhydrophilic surfaces. |
Product of the Month - Precision Combo Calibration Device |
While ramé-hart offers a variety of
calibration products, the
Precision Combo Calibration Device (p/n
100-27-31-U) is the only one that's required and also included with each
instrument we sell. Our DROPimage software has a calibration routine^{1}
that will take a picture of the sphere which results when the
calibration device is positioned on the stage and in focus and then
analyzes the resulting profile. Knowing the diameter of the ball, a
value (in microns) of the pixel size in both the x and y axes is
calculated. These dimensional values are then stored in DROPimage and used to
determine both linear and angular distances. Since all measurements
reference back to the calibration device of a known dimensional value,
the resulting data are both correct and valid.
For customers working within certain quality standards, we also offer a certified version of the Precision Combo Calibration Device (p/n 100-27-31-C). This version of the calibration tool ships with a NIST-traceable certificate which optionally can be renewed annually. ^{1} Watch this video to see how easy it is to calibrate a ramé-hart instrument using a Precision Combo Calibration Device and DROPimage Advanced. |
Regards,
Carl Clegg |