Everything in nature has a geometric pattern—from the tiger’s stripes and spirals in flowers to the unique fingerprints of each human being. While these patterns are sometimes symmetrical, most of such patterns lack symmetry, which leaves us with one major question: How do such unsymmetrical patterns emerge in nature?

Studies report that drying environments cause water evaporation and can lead to the formation of asymmetric patterns during biological growth through a phenomenon called “symmetry breaking.” Although reported through mathematical studies, these studies lack physical-chemical experiments that replicate this phenomenon.

A recent study at the Japan Advanced Institute of Science and Technology (JAIST), led by Associate Professor Kosuke Okeyoshi and doctoral student Thi Kim Loc Nguyen, uncovers the mechanisms behind symmetry breaking during a process called meniscus splitting in evaporating polymer solutions. The findings of the study were published in Advanced Science on June 3, 2025.

Meniscus splitting is the geometric division of a single evaporating liquid interface into multiple segments, typically observed when viscous fluids like polymer solutions are evaporated in confined spaces. Crucially, this division occurs in an asymmetric fashion, breaking the spatial symmetry of the original system.

In his previous studies, Dr. Okeyoshi had reported that meniscus splitting in evaporating polymer dispersions forms dissipative structures—systems that form and maintain order despite being far from thermodynamic equilibrium. Such structures are commonly seen in natural systems, including biological tissues, chemical reactions, and weather patterns.

“We had previously reported meniscus splitting as a dissipative structure phenomenon, but the precise mechanisms guiding the symmetry and positioning of split interfaces during evaporation were poorly understood—until now,” explains Dr. Okeyoshi.

Using controlled experiments and probabilistic analysis, the researchers tried to uncover the mechanism behind the unsymmetrical meniscus splitting. They observed that the splitting of the liquid interface doesn’t occur evenly. Instead, the nucleation points—the spots where the split begins—form at uneven, unpredictable positions along the confined space. This symmetry breaking and its time of occurrence vary significantly depending on different factors like the width of the container and the fluid’s properties.

For the experiments, the researchers used chitosan, a biocompatible polysaccharide, as the polymer material. When the polymer solution evaporated under controlled conditions, the interface split into either two or three sections, with clear deviations from symmetric positions. Focusing on conditions where the interface splits into two or three, the team examined nucleation positions in detail.

Statistical analysis revealed that symmetry breaking and asynchronous nucleus formation occur with each split type and are interrelated. In binary splits, nuclei tend to form off-center, and this displacement becomes more prominent with increasing cell width. In ternary splits, the second nucleation’s timing and position significantly affect asynchronous nuclei formation. These two aspects are crucial to understanding time evolution in such phenomena.

Additionally, the spacing between nuclei was influenced by the capillary length at the interface between the liquid phase of the polymer solution and air. The spacing is greater than twice the capillary length. In this study, a viscous polysaccharide solution of chitosan was used, with a capillary length of around 5 mm. This phenomenon has also been demonstrated with other polysaccharides, contributing to a wider understanding of pattern formation.

The simple exploration of the splitting process in this study contributes to the fundamental understanding of symmetry breaking and synchronous generation in natural patterns, with practical applications in designing and optimizing polymer-based materials and processes.

“This work bridges a gap between theoretical pattern formation and real-world physical behavior, with insights also applicable to the natural world,” says Dr. Okeyoshi. “Our results not only deepen our understanding of non-equilibrium systems but also offer potential applications in materials science, evolutionary ecology, and meteorology.”

While the finding is a significant milestone in polymer science, the implications extend far beyond impacting multiple fields, including colloid science, interfacial science, materials science, fluid dynamics, non-equilibrium science, and life sciences. Furthermore, integration of these findings with mathematics, simulation, and data science may promote further development in pattern formation theory and material design.