Analyzing nano- and microscale fluids

Scientists that simultaneously perform optical microscopy, measurement, and characterization of tiny volumes of fluids of varied viscosity encounter challenges when examining volatile and low-viscous nanodroplets and thin films, especially when these are significantly influenced by small changes within their immediate microenvironments. For example, the Earth’s 3D magnetic field can interfere with the focal plane of an optical microscope. In a recent investigation, researchers at Clemson University addressed these challenges using their novel optical microscope stage design which contains five magnetic coils and a microTesla rotating magnetic field within the focal plane of the microscope objective. They report their findings in Physics of Fluids in July 2017.

Characterization of large volumes of complex and highly viscous liquids, such as surfactants, biopolymers, and salt solutions, via in situ rheological analysis can be achieved using magnetic rotational spectroscopy which, according to the authors, was proposed by Yakov Frenkel in the mid-20^th century. By placing magnetic probes within the focal plane of the optical microscope, the researchers achieved on-demand cancellation of the Earth’s 3D magnetic field and other ambient bias fields to more precisely analyze samples, creating a minimized magnetic gradient and uniform magnetic field, and controlled sample exposure to environmental factors, such as gas composition and humidity, which could undesirably influence the microscopy.

Author Konstanin Kornev feels that this approach can be effectively used in other important applications, such as characterizing potentially hazardous emulsion droplets and scarce biological remains. Kornev also emphasizes that this analysis approach offers many opportunities for studying new phenomena at the nano- and microscale.

Source: “Magnetic stage with environmental control for optical microscopy and high-speed nano- and microrheology,” by Pavel Aprelev, Bonni McKinney, Chadwick Walls, and Konstantin G. Kornev, Physics of Fluids (2017). The article can be accessed at https://doi.org/10.1063/1.4989548 .