Credit: NIST
Colorized plot of the light-assisted curing of a polymer over five seconds, as measured with NIST’s custom atomic force microscope with a nanocylinder probe. Darker colors indicate a higher level of conversion from a liquid resin to a polymer. The magenta block at left represents the light fixture that initiates the reaction.
In a step toward making more accurate and uniform 3D-printed parts such as personalized prosthetics and dental materials, researchers at the National Institute of Standards and Technology (NIST) have demonstrated a method of measuring the rate at which microscopic regions of a liquid raw material harden into a solid plastic when exposed to light.
NIST’s custom atomic force microscope (AFM) with a nanometer-scale, cylinder-shaped tip revealed that the complex process of curing resins, as they react under light to form polymers, requires controlling how much of the light’s energy goes into forming the polymer and how much the polymer spreads out, or diffuses, during 3D printing.
Described in a new paper, the NIST experiments showed that overall light-exposure conditions, not just the total optical energy as often assumed, control how far the polymer diffuses. For example, increasing light intensity for a constant or shorter duration reduced resin-to-polymer conversion and could distort the shape of a printed part. The measurements required only a few microliters of resin, offering a way to reduce the costs of making and testing novel resins.
“This research really digs into the unique process and materials science insight afforded by our new metrology techniques,” project leader Jason Killgore said.
The work builds on the NIST team’s prior development of a related AFM method — nanocylinder vibrations quantify polymer curing printing
