Powder Wetting

The study of wetting of powders and porous solids involves determination of contact angles or graphing the change in contact angles over time. For more on theory click this link.

Methods used to characterize powder wetting

Washburn Technique

A solid plug of powder is brought into contact with the wetting liquid. The liquid imbibed by the plug (as measured by volume or mass) is monitored against time after contact.  An alternative approach uses the coating of a powder slurry on a solid support (such as a microscope slide) and treating this sample the same as the powder plug. Graphical and mathematical analysis of data from two or more wetting liquids yields "apparent contact angle". Applies only with liquids which wet but do not dissolve powder tested.            For more on theory click this link.

Instruments which use Washburn technique to determine contact angles:

Sigma 700 the finest tensiometer available. Fiber range microbalance accurate to 1 microgram. Expansive software package includes powder wetting by Washburn method . Measurement by change in mass. Effect of packing sleeve may be subtracted from data. Complete data reduction included.

Sigma 701 computer controlled research quality tensiometer. Software package includes powder wetting by Washburn method . Measurement by change in mass. Effect of packing sleeve may be subtracted from data. Complete data reduction included. Modular construction allows upgrade to full Sigma 701 capabilities. Accurate to 0.01 mN/m.

Goniometry

Powder is compressed to produce a flat surface. A drop of the wetting liquid is placed on the surface and contact angla is assayed against time. Can be used with both wetting and non-wetting liquids.                  For more on theory click this link.

Instruments which use goniometry to measure contact angles

Theta research quality computerized goniometer. Strobed monochromatic LED light source, telecentric optics and high speed camera yield exceptional quality images. Data reduction software includes profile fitting to Young-Laplace equation for most accurate contact angle measurements available. On screen trigger and high speed image capabilities allow for studies of rapid wetting substrates. 

Theta Lite low-priced goniometer with computer assisted data reduction. Uses firewire camera and LED lighting. Get the power of sophisticated computer image analysis in an economical package.

Wilhelmy Plate Tensiometry

Powder is compressed to form a flat plate and treated as a solid with Wilhelmy plate contact angle studies. Deformation or dissolution of plate after initial contact may prevent assay of receding angles. Alternately powders can be adhered to a solid support (using tape or adhesive) and studied.   See also Wilhelmy plate contact angles.

Instruments which use Wilhemy method for contact angles.

Sigma 700 the finest tensiometer available. Fiber range microbalance accurate to 1 microgram. Experiments included in expansive software package allow study of wide range of solid substrates including fibers of less than 10 micron diameters.

Sigma 701 (with software upgrade) computer controlled research quality tensiometer. Capable of full range of Wilhelmy method contact angle measurements except very small samples. Modular construction allows upgrade to full  Sigma 701 capabilities. Accurate to 0.01 mN/m.

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