Rougher Materials Get Along Better: Surface Roughness Influences Nanoparticle Attachment

The Science

Nanoparticles in solution can attach, assembling into complex structures. Researchers used cubic phase sodium yttrium fluoride (a-NAYF) as a model system to understand forces that control particle attachment under an optical field. They found that the surface roughness of the a-NAYF particles played a significant role in their attachment behavior. Rougher particles were more easily able to collide and attach. Simulations showed that the hydrodynamic resistivity drastically differs based on surface roughness and leads to the observed differences in attachment behavior.

The Impact

The behavior of nanoparticles in solution is important to nanoscience and nanotechnology in general, impacting fields as varied as non-classical crystal growth, nanophotonics and modern material design, colloidal dispersion processing, and nanoparticle transport. Identifying the influence of surface roughness on nanoparticle attachment can help scientists more accurately predict the behavior of nanoparticles in solution. Particle dynamics that have been relatively ignored need to be considered as a key factor to control the behavior of real systems.

Summary

The interactions involved in colloidal dispersions of nanoparticles affect their assembly pathways and the resulting structures. Understanding nanoparticle behavior is critical to the predictive design of precursor colloidal systems and their conversion to materials with pre-determined properties. Despite much prior work on nanoparticle assembly, a rigorous understanding of the interplay between particle forces that lead to contact between colloidal particles has remained a persistent challenge. Using unique characteristics of an optical field, researchers directed the assembly of individual nanoparticles of cubic phase sodium yttrium fluoride to better understand the forces behind particle attachment. The results showed that decreasing the smoothness of spherical nanostructures increases their ability to collide and assemble in solution under an external optical field. This observation was supported by theoretical models for hydrodynamics of rough particles, coupled with Langevin dynamics simulations to predict the contact of nanoparticles in solution. This work provides a fundamentally new and counter-intuitive insight into the assembly of colloidal nanostructures, revealing the critical roles of particle dynamics and surface roughness and paving the way for the design of surface textures as additional degrees of control over synthesis processes. 

Contact

Jim De Yoreo, Pacific Northwest National Laboratory, james.deyoreo@pnnl.gov 

Funding

Transmission electron microscopy of materials and the development of theories for all simulations and analyses were supported by the U.S. Department of Energy (DOE), Office of Science, Basic Energy Sciences (BES), Materials Sciences and Engineering Division, Synthesis and Processing Science Program, FWP 67554. The development of the Langevin dynamic and hydrodynamic simulations was partially supported by DOE BES Chemical Sciences, Geosciences, and Biosciences Division, Chemical Physics and Interfacial Sciences Program, FWP 16249.