Rheometer performs standard testing using a fraction of normal sample size requirements

For many laboratory procedures in chemistry, such as nuclear magnetic resonance spectroscopy and gel permeation chromatography, 10 to 20 milligrams of a new sample is an ample amount to conduct all tests. Rheological measurements, however, often require upwards of 50 mg in a sample, an amount that is prohibitive for some labs. New work points to a path forward for more sensitive rheometers requiring less sample.

Wu et al. developed a miniaturized sliding-plates shear rheometer, named mgRheo, that requires merely 2 mg of sample. Using a flexure-based force-sensing device coupled with a laser interferometer to measure displacement, it can measure forces in milli- and micronewtons. The device performs standard rheological tests such as small amplitude oscillatory shear, step strain, and stress relaxation.

“We want to explore the rheology and dynamics of new kinds of polymers. The question is how new architectures and structures influence their dynamics,” said author Gengxin Liu. “In other words, how would such molecules and polymers diffuse?”

Testing on polydimethylsiloxane viscoelastic standard, entangled poly(hexyl methacrylate), and polystyrene, mgRheo performed comparably with commercial rheometers. When overfilled with the sample, however, moduli measurements became systematically higher by up to 30 percent. Despite this, the device still provided reliable rheometric measurements, especially obtaining linear viscoelasticity on soft matters that are synthetically difficult to obtain in a large quantity.

The laser interferometer also provides the freedom to heat the samples as needed without worrying about damage or disturbance to the displacement-measuring device.

Liu hopes that such work encourages others “to think out of the box (of instrument manufacturers)” and will attract collaborators to characterize new rheological phenomena.

Source: “Micronewton shear rheometer performing SAOS using 2 mg of sample,” by Weiwei Wu, Jintian Luo, Xikai Ouyang, Wangjing He, Kangle Bao, Hui Li, and Gengxin Liu, Journal of Rheology (2022). The article can be accessed at https://doi.org/10.1122/8.0000494 .