How a Viscometer/Rheometer-On-A-Chip Works

Understanding the viscosity is a crucial aspect of manufacturing operations in many industries worldwide. In order to fulfill customer demands of product consistency and quality, viscosity measurement becomes even more important.

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Problem: Understanding the viscosity is a crucial aspect of manufacturing operations in many industries worldwide. In order to fulfill customer demands of product consistency and quality, viscosity measurement becomes even more important. Viscosity is the resistance to flow by definition. Numerous technologies or methods have been developed and used to measure the resistance. Those are spindle-rotation, acoustic, falling ball, and glass capillaries to name a few. These methods simply give “index” rather than measuring “the true viscosity” for non-Newtonian liquids for which viscosity changes with shear rate (or flow rate). This is because most of these technologies are designed for simple Newtonian liquids. However, non-Newtonian liquids comprise most liquid products in the world. Different methods measure different indexes for the same liquids, which make cross referencing extremely difficult. To measure true viscosity, users have to resort to more sophisticated rheometers. However, these instruments are expensive and require lengthy time and higher level of training for use.

Additional problems are that current viscometers require larger amount of sample volume and limited to narrow shear rates. Larger volume requirements make viscosity measurement very difficult for precious samples and even larger volume of cleaning solution needs to be consumed after test. Limited (or no) shear rate accessibility from these viscometers makes it impossible to characterize properly the liquid flow behavior during fast processes such as printing, coating, inkjetting, and spraying.



RheoSense’s new micro-liter viscometer using lab-on-a-chip technology

Solution: m-VROC® (Viscometer/ rheometer-on-a-chip) is state of the art viscometer that measures “true viscosity”. Its measurement principle is based on pressure drop measurement of a flow in a well defined rectangular microfluidic channel: the principle is well described in numerous rheology textbooks (for example, Rheology Principles, Christopher W. Macosko). Liquid flow through the microfluidic channel generates resistance, which in turns generates pressure drop. By measuring the pressure drop at a known flow rate, viscosity is measured. By varying the flow rate, true viscosity is measured as a function of shear rate. With m-VROC (see photo above), viscosity measurement is easy and fast. Sample loaded into a syringe is pumped to flow to the VROC® chip in silver enclosure. As the flow rate is controlled by the syringe pump and the VROC® chip senses the pressure drop, thereby, measuring viscosity.

In addition to the ability of measuring true viscosity, small measuring cell of VROC® enables viscosity measurement for small sample volume (as small as 50 microliters) and viscosity measurement at high shear rates. The VROC® chip has been used to measure wide range of liquids and viscosities.

The fast and easy-to-use m-VROC increases the test throughput. Accuracy and repeatability of the viscometer helps determine consistency to the next level.

For more information, go to www.kdscientific.com.

Categories: How it Works

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Published: October 1, 2009

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