ADVANCED MATERIALS & PROCESSES | JULY/AUGUST 2025 68 3D PRINTSHOP WATER SCULPTING TECHNIQUE CLEANS SURFACES By exploiting water surface tension, physicists from the University of Liège are creating programmed liquid reliefs capable of guiding particles under the action of gravity alone. This is a promising advance for microscopic transport and sorting, as well as marine pollution control. The team 3D printed conical spines close enough together to deform the surface of water on a large scale. “Each spike creates a meniscus around itself,” explains physicist Megan Delens. “Following this logic, this means that if we align them well and they are close enough together, we should see a sort of giant meniscus appear, resulting from the superposition and addition of each individual meniscus.” By modifying each spine individually, the surface of the liquid no longer remains flat, but forms a kind of “programmed” liquid landscape. “Programmed” because it is by changing the height or distance between the spines that the researchers have been able to design liquid interfaces that follow all sorts of topographies: inclined planes, hemispheres, but that also draw much more complex shapes. This method also offers a new way of moving and sorting floating objects such as marbles, droplets, or plastic particles. When the liquid surface slopes, the lighter objects rise and the denser ones sink under the action of their own weight, as if they were sliding down a hill of water. This passive approach could be used in micro- manipulation, particle sorting, or even cleaning liquid surfaces, for example, to capture microplastics or oil droplets on the surface of water. www.ulg.ac.be. EMITTER CREATES ACOUSTIC RAINBOW A 3D-printed device, called an acoustic rainbow emitter (ARE) takes in broadband white noise signals and radiates the sound equally. Similar to how a prism splits white light into a rainbow, the ARE device steers each frequency in different directions, creating an acoustic rainbow. The freedom of 3D printing allowed the team from Technical University of Denmark and Universidad Politécnica de Madrid to iteratively adjust the shape of solid material to control the sound emitted to match a specific pattern across frequencies. The researchers also used the Helmholtz equation to simulate sound propagation and scattering in the air around a rigid, sound- reflecting structure. dx.doi.org/ 10.1126/sciadv.ads7497. MICROSCALE PRINTING CHANGES COLOR ON-DEMAND Researchers have developed a microscale 3D-printing technique that allows them to adjust color. Their findings, published in PNAS Nexus, describe how they used an electric field-coupled two-photon polymerization (TPP) system for on-demand modulation of 3D-printed color. The resin they used is made of oblique helicoidal cholesteric liquid crystals, a material that changes color when exposed to electric fields of varying strengths. The electrical current changes the angle of bent-shaped liquid crystals, which changes how the crystals look under white light, moving from violet to green to red as the field strength decreases. A pattern can be printed in different colors by selectively printing certain parts at one driving electric field strength and other parts at a different driving electric field strength. dx.doi.org/ 10.1093/pnasnexus/pgaf074. By modifying each spine individually, the surface of the liquid forms a kind of programmed liquid landscape. Courtesy of Université de Liège/M. Delens. Printed 2D and 3D microstructures in different structural colors: (a) 2D Max Planck Society logo, (b) 2D Taiji logo, and (c) 3D microscale frames. The frames are printed in liquid crystal cells with a 65 µm gap at different driving electric field strengths. Courtesy of PNAS Nexus, 2025. (a) (b) (c)
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