AR-G2/AR 2000ex/AR 1500ex Getting Started Guide Page 37
The Interfacial Double Wall Ring (DWR)
The Interfacial Double Wall Ring (DWR) measuring system measures the viscous and linear viscoelastic
properties of the interface between liquid-liquid and liquid-air. It consists of a thin, square-edged ring and a
Delrin
®
trough with a circular channel. The ring and support legs are constructed from a platinum/ iridium
(Pt/Ir) alloy, for chemical inertness, ease of cleaning, and wettability. The ring support is made of stainless
steel. It is important that the ring and trough are perfectly aligned (concentricity), and the trough positioned
on the Peltier Plate accurately leveled.
A non-return (check) valve is fitted to the trough below the level of the interface. Together with the
supplied tubing and syringe, this can be used to adjust the lower fluid level, or to add an active ingredient.
NOTE: The fabrication process used for the DWR will result in more runout than our standard cones and
plates. The total runout of the DWR is inspected using a 3D laser technique and has to be better than
0.5 mm to pass inspection. This value was determined from the influence on sample measurements taken
during the development process. The human eye can generally perceive a total runout greater than
0.05 mm, so the DWR will always appear to “wobble” when rotating, even when within specification.
Figure 16 Interfacial DWR.
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