Twente researchers use gravity and UV light to predict fiber formation

The University of Twente in the Netherlands reported on October 8 that researchers used gravity and ultraviolet light to predict how a falling liquid resin becomes a thin solid fiber. The experiment addresses a difficult problem in fiber production: determining the final thickness when a pulling force, rather than a controlled drawing speed, stretches the material.

The announcement describes work by Jan Siemen Smink, CW. Visser and H. Lhuissier published in Physical Review Letters on October 2. Its contribution is a controlled way to examine solidification and predict the resulting fiber, rather than the invention of making fibers with light.

How gravity and UV light form a fiber

Smink, of Twente’s Faculty of Engineering Technology, and his colleagues pumped a photocurable resin containing a photoinitiator through a vertical nozzle at constant flow. Gravity stretched the descending liquid jet, which was collected in a water bath between 100 and 400 millimeters below the nozzle.

UV illumination from four sides was focused about 5 millimeters beneath the nozzle, over an effective length of 1.93 millimeters. The researchers used light intensities ranging from 0.5 to about 6 kilowatts per square meter, allowing them to examine how illumination affected the transition from liquid to solid.

Solidification times reached approximately 10 milliseconds. The measured fiber radii ranged from about 0.13 to 0.23 millimeters. These measurements describe the radius, not the full width of the fibers.

A separate demonstration intercepted illuminated and unilluminated jets with a plate. Only the illuminated material retained its shape on collection, according to the university. That observation demonstrated solidification; it was not a standardized test of fiber strength.

What the experiment can predict

The paper, Fast Solidification of a Gravity-Stretched Liquid Jet, distinguishes between spinning at a controlled drawing speed and spinning driven by a force. Final radius is harder to predict in the latter case. The experiment simplifies that problem by concentrating the liquid-to-solid transition within a sharply localized region.

The authors report that light intensity and solidification kinetics determine where the jet solidifies. Gravity, inertia and capillary forces govern the fiber radius, its behavior immediately after illumination begins and the jet’s stability. Their results also address whether the material forms fibers or beads, including when solidification is intermittent.

According to Physics Magazine, combining a momentum balance with polymerization kinetics produced a parameter-free equation that predicted the measured final radii. That agreement applies to the experimental configuration tested; it does not establish equivalent predictive control across all polymers or spinning methods.

“Most manufactured fibers are spun,” Aix-Marseille researcher Henri Lhuissier told Physics Magazine. He identified the interaction of chemistry, phase changes and fluid mechanics as an obstacle to prediction. Twente fluid-dynamics expert Detlef Lohse said the work combined careful experiments with deep theoretical analysis. Lohse shares an institution with members of the study team.

Earlier research on light-cured fibers

Earlier work by Princeton researchers Malcolm Slutzky, Howard A. Stone and Janine K. Nunes already examined pulsed UV light in continuously flowing photocrosslinkable liquid. Their manuscript, A quantitative study of the effect of flow on the photopolymerization of fibers, describes experiments and modeling of soft microfiber production.

That team modeled reactive radicals and molecular oxygen along the illuminated flow, comparing predicted fiber-forming conditions with observations. It distinguished settings that produced no polymerization, nonuniform fibers and uniform microfibers, and reported predictable control of fiber length over a range of operating parameters.

The Princeton work also explained how pulsed light could create segments during formation, instead of requiring a continuous fiber to be cut afterward. It provides independent technical precedent for controlling fibers with light, rather than a replication of the new gravity-driven experiment.

What remains unproven for manufacturing

Physics Magazine reports that the team intends to investigate more gradual solidification and stronger air drag. Those questions extend beyond the sharply localized transition used here. Reducing manufacturing trial and error is a suggested benefit, not a demonstrated factory outcome.

The published accounts establish laboratory measurements and predictions, but do not demonstrate production-cost savings, improved textile performance or commercial deployment. Although the university discusses thickness and strength as broader challenges in fiber formation, its announcement does not quantify a strength improvement.