A polymer that can be modified quickly with low-power lasers emitting infrared and visible light could provide a safe, inexpensive method to produce polymer surfaces for biomedical devices, electronics, information storage, microfluidics, and other applications. The photosensitive polymer, made from elemental sulfur and low-cost dienes, was discovered by researchers at Flinders University during a routine chemical analysis. “The novel polymer was immediately modified by a low-power laser — an unusual response I had never observed before on any other common polymers,” researcher Christopher Gibson said. The polymer identified by Gibson was invented in the lab of Flinders University professor Justin Chalker in 2022. The research team further investigated the polymer’s atypical reaction, conducting a detailed analysis of how low-power laser beams modified the polymer and how the type and size of the modifications could be controlled. Researcher Abigail Mann (left), next to the low-power laser, Australian National Fabrication Facility spectroscopist Jason Gascooke (center), and researcher Lynn Lisboa (right) with the “micro-Lisa” laser image displayed on a regular computer screen. Courtesy of Flinders University. Using low-power, continuous wave lasers with wavelengths of 532 nm, 638 nm, 690 nm, and 786 nm, the researchers made a variety of surface modifications to copolymers made from sulfur and either cyclopentadiene or dicyclopentadiene. By controlling the power, wavelength, and beam diameter, the researchers were able to install spikes, raised dots, pits, channels, and holes on the polymer surfaces. The modifications were rapid, with exposure times on the millisecond to second timescales. The inclusion of maghemite (γ-Fe2O3) nanoparticles in the polymer matrix facilitated modification at lower laser powers. The researchers were able to erase the polymer’s swelling modifications by heating the sample in an oven at 160 °C, but could not erase ablated areas because of an irreversible loss of sulfur species from the polymer in these regions. The team demonstrated the synthesis and laser-induced modification of the photosensitive polymer systems in examples of direct-write laser lithography and erasable information storage, featuring a laser-etched version of da Vinci’s Mona Lisa and micro-Braille printing smaller than a pinhead. Many applications, from biomedical devices to microfluidics, rely on the ability to modify polymer surfaces using laser light. Typically, these modifications are made with high-power lasers that require specialized equipment and facilities. Additionally, polymer systems that can be easily modified by lasers are often complex and costly to prepare. The ability to modify polymers using low-power lasers could facilitate new approaches to storing data on polymers, new patterned surfaces for biomedical applications, and new ways to make micro- and nanoscale devices for electronics, sensors, and microfluidics. Courtesy of Flinders University. The simple approach of the Flinders team, using low-cost materials and low-power laser systems, compares favorably to other methods of lithography that require complex polymer structures, high-power lasers, and multi-step masking, developing, and washing protocols. “This could be a way to reduce the need for expensive, specialized equipment, including high-power lasers with hazardous radiation risk, while also using more sustainable materials,” Chalker said. “For instance, the key polymer is made from low-cost elemental sulfur, an industrial byproduct, and either cyclopentadiene or dicyclopentadiene.” Potential applications for the new approach to modifying polymer surfaces with low-power lasing could include methods to store data, develop patterned surfaces for biomedical applications, and make microscale and nanoscale devices. “The impact of this discovery extends far beyond the laboratory, with potential use in biomedical devices, electronics, information storage, microfluidics, and many other functional material applications,” researcher Lynn Lisboa said. “The outcome of these efforts is a new technology for generating precise patterns on the polymer surface,” researcher Abigail Mann said. “It is exciting to develop and bring new microfabrication techniques to sulfur-based materials. We hope to inspire a broad range of real-world applications in our lab and beyond.” The research was published in Angewandte Chemie International Edition (www.doi.org/10.1002/anie.202404802).
