A research team from RMIT University in Melbourne, Australia, has developed a new coating technology that uses high-frequency sound waves to atomize liquids into micron-sized aerosol droplets, forming a uniform and dense "invisible protective layer" on various fine surfaces without heating or damaging the substrate. Researchers applied this method to the leaves of the common indoor foliage plant Pothos (Epipremnum aureum) for the first time, effectively blocking harmful ultraviolet (UV) rays without affecting photosynthesis, vividly demonstrating its gentle yet highly effective ability to protect "fragile living organisms".
The core of this work is to use acoustic microfluidics (acoustomicrofluidics) technology to control the liquid precursor so that it is stretched and "broken" on the surface of a tiny chip that can generate ultra-high frequency sound waves of about 10 MHz, forming a delicate aerosol cloud. When these droplets fly through the air and are deposited on a target surface, they self-assemble into a type of covalent organic framework material (COFs), forming a protective coating that is only microns thick but has a continuous structure and well-defined functions. This integrated "atomization + film formation" process can be completed at room temperature and pressure in open air. It does not require high temperatures, long-term reactions or strict laboratory environments commonly used in traditional coating processes, which greatly reduces the requirements for materials and environment.
Covalent organic frameworks are a type of highly porous and crystal-ordered materials, often described as "molecular scaffolding" with nanoscale holes. They can be structurally designed to achieve multiple functions such as absorbing light, capturing specific chemicals, or protecting surfaces. However, in past applications, the construction process of COFs has been extremely "picky": it usually requires precursors to react at high temperatures for a long time, the process is complex and the conditions are harsh. It is difficult to scale up and is not suitable for use on sensitive substrates such as plant leaves and flexible films. The research team pointed out that in traditional processes, it is often necessary to make a difficult choice between "maintaining the orderly structure of the material" and "avoiding damage to the coated surface", and the sonic atomization platform provides a new way to break this dilemma.
In this experiment, the researchers used plant leaves as test objects to verify the performance of the coating on real biological surfaces: the COFs coating can selectively absorb harmful ultraviolet rays while allowing visible light to pass freely, allowing plants to continue photosynthesis. The experiment showed that during the entire process of coating, UV irradiation and subsequent coating removal, the leaves showed no obvious signs of damage during the test period (60 days), highlighting the balance between protective effect and biocompatibility of this "sonic sunscreen spray". The research team regards this as a "proof of concept" and believes that this platform has the potential to be promoted and applied in more real-world interfaces, devices and biological systems.
In terms of technical route, the acoustic microfluidic platform adopts a chip-level design, which is small in size and light in weight. The working principle is to continuously stretch and split the precursor liquid flowing through it into stable fine droplets through ultra-high-frequency acoustic vibrations generated on the surface of the chip. When deposited onto a variety of surfaces, these mist droplets enable gentle and highly controlled coating deposition, even on soft tissues as thin as paper towels. The researchers emphasized that this method combines "manufacturing" and "coating" into one step, does not require additional heating or complex environmental control, and has obvious advantages in terms of process simplification and scope of application.
In terms of application prospects, the research team pays more attention to the possible uses of COFs coatings in highly sensitive materials and new generation devices, including textiles, plastics, glass, silicon-based electronic devices, etc. Many new electronic products, sensors and membrane materials are extremely temperature sensitive and cannot withstand traditional coating processes. However, they urgently need surface protection layers to resist light, corrosion or chemical attack. Sonic atomization technology fills this process gap. Scholars involved in the study pointed out that this method greatly expands the possibility of COFs from laboratory materials to practical applications, opening up a new situation for their deployment in environmental protection, functional coatings and biotechnology.
In terms of scalability, the research team believes that this chip-level acoustic platform is very suitable for integration with unmanned systems to perform large-area, refined spraying tasks. Thanks to the miniaturization and low-cost characteristics of the device, the platform can be installed on drones or autonomous vehicles to accurately coat crops or forest leaves, achieving large-scale "fixed-point sun protection" or other functional spraying in outdoor environments. Combined with the advantages of large-scale production brought by nanofabrication, researchers expect this technology to be deployed on a large scale in future biotechnology and environmental engineering applications.
Currently, this technology has submitted a provisional patent application in Australia, and related research papers have been published in the academic journal "Science Advances". The research team stated that they will further evaluate the stability and durability of the coating under long-term exposure conditions in the natural environment, and explore its practical solutions in electronic device protection, chemical protective films, and other sensitive interfaces. While questions about outdoor weatherability remain to be answered, this new method of manufacturing and depositing coatings that relies on sound waves has shown the potential to disrupt existing process paradigms.