3-in-1 rheo-Raman microscope revealed
Image: NIST researcher, Anthony Kotula, using the rheo-Raman microscope, a three-in-one instrument to measure the flow properties of a material alongside microscopic structure and composition.
A novel rheo-Raman microscope allows scientists to correlate the flowability of soft materials, including gels, molten polymers and biological fluids with the underlying microstructure and composition.
Developed by researchers at the National Institute of Standards and Technology (NIST) and Thermo Fisher Scientific, the instrument provides a clearer picture of how structural make-up and flow behaviour during processing dictate macroscopic properties, including strength, hardness and electrical conductivity.
The new research tool couples a Raman spectrometer and optical microscope to a rotational rheometer through an optically transparent base.
As NIST materials scientist, Anthony Kotula, highlights: "The new instrument is designed for 'multitasking'... and the resulting simultaneous measurements are particularly advantageous in situations where flow properties vary due to either chemical or conformational changes in molecular structure, such as in crystallization, melting, gelation, or curing processes."
“It allows you to trace the evolution of microstructure across a range of temperatures and to do it in one controlled experiment rather than in two or three separate ones," he adds. "It provides insights that would be very difficult to obtain through measurements made one at a time."
Kotula believes homing in on the flow behaviour is especially important, because it is intimately coupled with the microstructure and ultimate properties.
As he highlights, soft materials share features of liquids and solids.
These materials range from plastics to liquid crystal displays and from contact lenses to biopharmaceuticals.
For these "in-between materials", even slight variations in processing conditions can alter internal structures and drastically change material properties, which can open the door to improved performance or entirely new technological applications.
Kotula and colleagues used their prototype rheo-Raman microscope to track and measure changes before, during and after melting a cosmetic material composed of coconut, almond oils and about ten other ingredients.
The researchers also presented simultaneous “melt” measurements taken on high-density polyethylene, corrosion-resistant pipes and many other items, as liquid molecules arranged and solidified into crystals.
Both demonstrations yielded a detailed, unfolding picture of how flow behaviour and other phenomena during melting and crystallisation correspond to changes in the shape and arrangement of molecules due to processing conditions.
“The rheo-Raman microscope is a general purpose instrument with lots of potential uses,” says Kotula. “At NIST, one of our first applications pertains to 3D printing. We’ll use it to better understand how polymer crystallization proceeds during the layer-by-layer printing process.”
Research is published in Review of Scientific Instruments.