In the relentless pursuit of precision at microscopic scales, controlling the behavior of ultra-small droplets has become a pivotal challenge across multiple advanced fields, including manufacturing, pharmaceuticals, and biomedical diagnostics. As droplets shrink to pico- and nanoliter volumes—millions of times smaller than a typical raindrop—their interaction with surfaces transforms dramatically. Minor imperfections at the solid interface cause significant frictional forces that inhibit their smooth and predictable movement. Overcoming these tribological hurdles is critical for innovations in microfluidics and lab-on-a-chip technologies, where manipulation of minute liquid quantities must be both precise and efficient.
A breakthrough study spearheaded by Dr. Mizuki Tenjimbayashi at the Research Center for Materials Nanoarchitectonics (MANA), Japan, proposes an ingenious alternative to the classical approach: instead of striving to engineer flawlessly smooth surfaces, the researchers coat the droplets themselves with a specially designed nanoparticle layer. This paradigm shift moves the challenge from surface fabrication to droplet modification, allowing ultra-small droplets to glide with near-frictionless ease on otherwise ordinary solid substrates. Their findings are detailed in the journal ACS Nano and have been recognized as the supplementary cover article, underscoring the innovation’s significance.
The team employed an ultrasonic spray technique to envelop pico- to nanoliter-scale droplets with a dynamic layer of fluorocarbon-modified fumed titania nanoparticles, each approximately 20 nanometers in diameter. This particle coating acts as a liquid-repellent shield that radically alters the droplet–surface interface. Instead of direct liquid–solid contact, which typically results in high friction due to adhesive forces and surface roughness, the droplet now slides atop a particle monolayer engaging in solid-solid contacts. This drastically minimizes resistance, reducing the sliding force to sub-nanonewton levels, orders of magnitude below previously reported thresholds.
One of the study’s most compelling aspects lies in its quantitative comparison across different droplet volumes. Their coating methodology decreases the volume threshold for maintaining liquid repellency by three to four orders of magnitude compared to conventional liquid-repellent surfaces. This implies that the scale at which near-frictionless droplet motion can be achieved is profoundly smaller, ensuring unprecedented control over fluids in the pico- and nanoliter regimes. The coating’s ultrastructure and chemistry are finely tuned to maintain this functionality without compromising droplet deformation capabilities.
Despite being encased by a particle shell, these micro liquid marbles preserve their intrinsic fluidic properties. They remain highly versatile entities capable of morphological transformations essential for microfluidic operations: merging with other droplets, splitting into smaller volumes, or re-shaping on command. This tunable flexibility is instrumental for applications demanding dynamic fluid manipulation, such as controlled chemical reactions or biological assays within micro-environments where reagent conservation and operational precision are critical.
The implications of this technology extend far beyond simple droplet transport. In the burgeoning fields of pico- and nanofluidics, where fluid volumes must be minimized to reduce waste and cost, such a coating technique could revolutionize device designs. Soft microrobotics, which rely on the controlled movement and deformation of encapsulated fluids, stand to benefit immensely from the near-frictionless motion enabled by this nanoparticle layer. This could catapult the efficiency and miniaturization capabilities of robotic components designed for delicate tasks at microscopic scales.
Moreover, this advance opens new avenues for collective droplet behaviors, where multiple droplets interact mechanically and chemically akin to particulate systems. Harnessing such behaviors could spawn novel microfluidic devices capable of complex fluid processing operations previously limited by frictional constraints. The ability to perform bioanalytical experiments or diagnostics with minimal sample volumes not only promises enhanced sensitivity but aligns with sustainability goals by drastically cutting reagent usage and chemical byproducts.
Fundamentally, this innovation exemplifies the broader scientific principle of nanoarchitectonics—designing material systems with precision at the nanoscale level to unlock emergent properties. By integrating chemically modified nanoparticles that confer super-repellent characteristics onto droplets, the MANA team has architected a liquid state that can navigate rough, everyday surfaces with unprecedented finesse. This work stands as a testament to the power of strategic nanoscale engineering in redefining fluid dynamics at extremes of scale.
While traditional attempts to reduce droplet friction focused on surface coatings that repel liquids, these approaches hit fundamental material limits when scaling down to pico- and nanoliter volumes. The significance of MANA’s approach resides in circumventing these boundaries by effectively making the droplet the entity that wears the repellency armor. It shifts the problem to a more controllable domain—the liquid’s immediate environment—yielding robust performance and greater adaptability.
Experimental validation involved detailed force measurements during droplet sliding, corroborated by microscopic observations of the particle layer’s structural integrity and behavior under mechanical stress. The coatings remained stable, dynamically adjusting to droplet shapes without catastrophic failure, ensuring consistent repellent effectiveness during complex operations like merging and splitting. This robustness highlights the potential for real-world integration in microfluidic devices.
In conclusion, the development of particle-coated “micro liquid marbles” represents a remarkable stride in miniature fluid management. It offers a scalable, highly effective method for manipulating droplets under conditions where friction previously posed insurmountable barriers. With broad application prospects spanning medical technology, chemical manufacturing, and fundamental physics, this nanoscale innovation heralds a future where the intricate dance of tiny droplets on surfaces can be choreographed with near-perfect grace.
Subject of Research: Nanoparticle-coated pico- to nanoliter droplets enabling near-frictionless motion on solid surfaces for microfluidic applications.
Article Title: Manipulating Pico- to Nanoliter Droplets on Surfaces without Sticking
News Publication Date: 6-Nov-2025
Web References:
- ACS Nano DOI: https://doi.org/10.1021/acsnano.5c14919
Image Credits: Dr. Mizuki Tenjimbayashi, Research Center for Materials Nanoarchitectonics (MANA), NIMS and VIZCIE
Keywords: Nanotechnology, Materials science, Microfluidics, Thin films, Engineering, Manufacturing, Medical technology, Chemistry, Physics
