Self-assembly of polymer-decorated nanorods: General principles and molecular dynamics simulations

• Applicant: Dr. Cheng-Wu Li
• Subject Area: Experimental and Theoretical Physics of Polymers ; Computer-Aided Design of Materials and Simulation of Materials Behaviour from Atomic to Microscopic Scale
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 536118308

In close collaboration with experiments on nanoparticle (NP) assembly into supercolloidal structures, this project aims to provide a deeper theoretical understanding of the physics behind the self-assembly of NPs through brush-decorated surfaces. A particular focus lies on the question of how essential parameters of the brush and the solvent affect the features of self-assembled structures that are found in the laboratory. Insights gained from this study are likely to provide clues about how these structures could be engineered in a systematic manner to provide the functionality that will be needed in future applications. Based on the scale of self-assembly system, we start with the basic building blocks-polymer-decorated nanoparticles (PDNs) - and explore the coupling effects between pairs of PDNs to probe the physical significance behind the experimental findings. First, for a single PDN, we will extend our previously developed mean-field theory to describe the brush conformations of PDNs for different NP sizes, polymer properties and solvent qualities. With molecular dynamics (MD) simulations, we will investigate the distribution of polymer graft points in relation to NP surface-curvature in good solvent, and the parameter range in which cohesive patches (as potential "binding sites" between different PDNs) are formed on PDN in poor solvent, respectively. Also, the effect of a mixture of good and poor solvents (as used in the experiments) on the PDN conformation, a mechanism that is not yet fully understood, is among the targets to be explored. Second, we extend our study to paired PDNs. The potential of mean field (PMF) between two PDNs is found in MD simulations by placing the objects at a sequence of different distances and monitoring the averaged forces between their mass centers. On this basis, we analyze the preferences for paired PDN contacts (e.g., side-by-side vs. tip-by-tip) as a function of chain length, grafting density and substrate charge density. Finally, for the simulation of a larger number of PDNs, in order to overcome the limitations of the available computational facilities, we plan to implement another level of coarse-graining, on which the entire brush layer is replaced by an effective mean-field potential. The PMFs obtained in the previous work will be approximated through a suitable parameterization and fed directly into the simulation software. This approach would drastically reduce the degrees of freedom, enable us to study the assembly of larger sets of PDNs, and understand the fundamental mechanisms of PDN assembly over several length scales. Depending on the speed of progress of this final module, extended sets of system parameters could be incorporated, in close coordination with the progress that takes place in the laboratory experiments.

• DFG Programme: Research Grants
• International Connection: China, USA
• Co-Investigator: Dr. Holger Merlitz
• Cooperation Partners: Professor Dr. Xue-Zheng Cao; Professor Dr. Sergei A. Egorov; Professor Dr. Chen-Xu Wu