First Author：Dr. Haochen Ye

Corresponding Authors and Affiliations：

Prof. Zhenjie Xue, Tianjin University of Technology；Prof. Tie Wang, Tianjin University of Technology

Original Article：https://doi.org/10.1021/jacs.5c19419

Background：

Droplet evaporation is a ubiquitous interfacial phenomenon that remains far from fully understood. From the ring-like deposits observed in the coffee-ring effect to applications in inkjet printing, micro/nanomaterial fabrication, and biomedical diagnostics, the evaporation pathway of a droplet on a solid surface often directly determines its final deposition morphology and functional performance.

Although droplet evaporation has been extensively studied, most current understanding is based on the assumption of ideal homogeneous surfaces. In real systems, however, interfaces often exhibit both structural and wettability heterogeneity. Whether droplets still follow a single predictable evaporation pathway under such heterogeneous conditions remains a fundamental and important scientific question.

Overview of the Work：

Recently, the research team led by Prof. Tie Wang and Prof. Zhenjie Xue at the Life and Health Intelligent Research Institute, Tianjin University of Technology, published a study in theJournal of the American Chemical Societythat systematically revealed the multimodal evaporation behaviors of droplets on heterogeneous interfaces and their underlying physical origins. The work further established a new framework for the predictable and controllable regulation of droplet evaporation.

Highlights：

To investigate droplet evaporation under realistic interfacial conditions, the researchers constructed a model system consisting of patterned nanoparticle superlattice arrays (Figure 1). Through controllable self-assembly and patterning techniques, nanoparticle-array domains were introduced onto a solid substrate, creating heterogeneous interfaces with distinct structural and wettability characteristics compared with the surrounding bare substrate.

Figure 1.Fabrication of patterned gold nanoparticle superlattice arrays

Using this model system, the team systematically examined the evaporation behavior of droplets on heterogeneous interfaces. As shown in Figure 2, three distinct evaporation modes were consistently observed:1.Mode 1: Directed contraction toward the center of the nanoparticle superlattice domain;2.Mode 2: Non-directed contraction away from the nanoparticle superlattice domain;3.Mode 3: Directed contraction accompanied by a characteristic “tailing” effect around the perimeter of the nanoparticle superlattice domain.These findings demonstrate that droplet evaporation on heterogeneous interfaces is not governed by a single mechanism but instead exhibits complex multimodal dynamics.

Figure 2.Different evaporation modes on heterogeneous substrates

To further uncover the governing principles behind these evaporation modes, the researchers systematically analyzed the evaporation dynamics associated with each mode (Figure 3). The emergence and transition of different evaporation modes were found to be regulated by the complex interplay among substrate contact-angle hysteresis, the receding contact angle of the nanoparticle superlattice domain, the initial droplet size, and their relative spatial configuration.

These results highlight the synergistic influence of wettability heterogeneity, droplet positioning, and droplet size on interfacial evaporation dynamics. Based on the experimental observations, the team further developed a unified theoretical framework to describe droplet evaporation behavior. By introducing a dimensionless parameter, G, they successfully linked the driving force for contact-line depinning with the pinning effect induced by nanostructures, thereby incorporating all observed evaporation modes into a common physical framework.

Figure 3.Dynamic evaporation processes under different evaporation modes

Droplet evaporation is not only a kinetic process but also directly determines the final deposition pattern of solutes at the interface. As shown in Figure 4, Raman spectroscopy was employed to verify the occurrence of different evaporation modes and to investigate their influence on analyte deposition.

Significant differences in deposition distributions were observed among the three evaporation modes. Notably, Mode 1 enabled highly concentrated and spatially uniform deposition of analytes, making it particularly attractive for sensing applications.

Figure 4.Comparison of analyte distributions after droplet evaporation

After establishing the physical picture of multimodal droplet evaporation, the researchers selected Exhaled Breath Condensate (EBC) as a practical model system to validate their evaporation-control strategy.

As illustrated in Figure 5, by exploiting Mode 1 evaporation, the platform enabled stable monitoring of hydrogen peroxide and pharmaceutical compounds present in EBC samples, demonstrating its potential for noninvasive health monitoring and disease diagnostics.

Figure 5Collection and monitoring of exhaled breath condensate

Conclusions and Outlook：

In summary, this work systematically reveals the multimodal nature of droplet evaporation on heterogeneous interfaces from both experimental and mechanistic perspectives. The study clarifies how droplet size, spatial positioning, and interfacial heterogeneity cooperatively determine evaporation pathway selection and demonstrates the decisive role of controllable evaporation dynamics in governing final deposition outcomes.These findings provide a new paradigm for understanding and regulating droplet behavior on complex interfaces and open new opportunities for advanced sensing, materials fabrication, and biomedical diagnostic applications.