Non-toxic liquid metal proves useful in rheological studies

Rotational rheometers are commonly used to study the rheological properties of fluids. These devices apply a shear deformation to fluids and measure their responses. When subjected to sufficiently high shear rates, viscoelastic fluids, such as epoxies and pastes, can experience edge fracture that complicates the interpretation of the resulting rheological measurements.

Edge fracture can be prevented by decreasing the rheometer gap size or increasing the interfacial tension of the fluid sample with its surrounding medium. While very promising, the latter method has received little consideration. Chan et al. studied the effects of increasing interfacial tension by immersing a fluid sample in a liquid metal alloy of gallium, indium, and tin.

“We used the non-toxic liquid metal Galinstan, commonly used by enthusiasts to cool computer hardware,” said author San To Chan. “It can be easily purchased from hardware stores or online shops.”

Study results showed that sealing the fluid sample’s free surface with Galinstan delayed fracture occurrence and extended the measurable shear rate range tenfold. This method eliminated all effects of edge fractures for a wide range of shear rates.

“Our proposed method allows researchers to probe the flow properties of viscoelastic materials at high flow rates. This may provide insight into natural phenomena and aid in optimizing industrial processes involving viscoelastic fluids, such as 3D printing and electronic packaging,” said Chan.

The researchers also note that Galinstan is immiscible with both water and oil. This property may eventually prove useful in evaporation prevention for different fluid samples during rheological experiments.

Source: “Prevention of edge fracture using a non-toxic liquid material sealant,” by San To Chan, Simon J. Haward, and Amy Q. Shen, Physics of Fluids (2022). The article can be accessed at https://doi.org/10.1063/5.0135554 .