The Washburn method measures the contact angle and surface free energy of porous materials like powders and textiles by observing how a liquid is drawn up into the material via capillary action. A glass tube filled with powder is dipped in a test liquid, and the liquid’s mass uptake over time is recorded. Treating the powder as many tiny capillaries, the relationship between mass squared (m2m^2m2) and time (ttt) is linear and described by the Washburn equation: m2=cσcos⁡θηρ×tm^2 = \frac{c \sigma \cos \theta}{\eta \rho} \times tm2=ηρcσcosθ​×t

• ccc is a capillary constant related to pore size and packing,
• θ\thetaθ is the contact angle,
• σ,η,ρ\sigma, \eta, \rhoσ,η,ρ are the liquid’s surface tension, viscosity, and density.

To find ccc, measure with a fully wetting liquid (contact angle 0∘0^\circ0∘), then use this to calculate θ\thetaθ for other liquids. Notes:

• Powder packing must be consistent since ccc depends on bulk density.
• Angles above 90° cannot be measured (no wetting). For these, drop shape analysis is used instead.

Drop Shape Analyzer DSA30R perform measurements of Interfacial Rheology and gives the relevant results for optimizing products and processes. The measuring principle of the DSA30R involves evaluating video images of drops or gas bubbles at a dosing needle to measure the surface or interfacial tension (SFI/IFT). The interface size is sinusoidally changed during this process. The SFT/IFT is measured as a function of the surface change and is also sinusoidal in the case of samples containing surfactants. The dosing unit’s extremely precise piezo drive enables exact sine waves in a frequency spectrum of 0.001 to 20 Hz, so the measurements cover a very wide dynamic range. Many innovations around the DSA30R turn formerly complex interfacial rheological analytics into an easy-to-perform method with quick sample changing. The filled glass syringe is inserted in a few simple steps and coupled automatically to the dosing feed. To determine the influence of temperature, or to make investigations of high-viscosity systems easier, the syringe is embedded in a temperature-controlled sleeve for measurements between -10 and 70 °C. The temperature of the surrounding phase can also be controlled. Moreover, the start of certain processes such as the beginning of oscillation can be automatically linked to the target temperature being reached. This ensures reproducible conditions without user intervention. Applications: - ■ Emulsions and foams for food or personal care ■ Flooding mixtures and foam in enhanced oil recovery ■ Demulsifiers ■ Defoamers and antifoamers ■ Surfactant research

The Drop Shape Analyzer – DSA100HP is our high-quality solution for the precision measurement of contact angle as well as surface and interfacial tension under pressures up to 1750 bar. In order to carry out the measurement, the DSA100HP’s high-resolution camera records video images of dosed drops through the pressure cell’s viewing windows and these are then evaluated in real time. DSA100 Series configuration.

• DSA100HP40 : Maximum Pressure – 40 bar (580 psi)
• DSA100HP690 : Maximum Pressure – 690 bar (10 000 psi) 
• DSA100HP1750 : Maximum Pressure – 1750 bar (25 000 psi)