Comparison between the early stages of compression in the experiment and simulations performed with different densities. The experiment was performed at room temperature with 6-nm gold nanoparticles.

Self assembled layers of nanoparticles at interfaces exhibit a complex dynamic behavior.  Under compression, a monolayer phase has been observed to transition into a trilayer, through intermediate phases characterized by the presence of macroscopic line patterns.  It has been shown, in a paper published in the Proceedings of the National Academy of Science, that these patterns can be explained by an equilibrium statistical mechanical theory.  The energy cost of the wrinkle pattern creation is, according to this theory, more than offset by an entropy increase, whereas the free energy of the system is lowered.  The model predicts two-phase coexistence and is in qualitative agreement with experimental observations.


Yenchao Chua, Brian Leahy, Minke Zhang, Siheng You, Ka Yee C. Lee, Susan N. Coppersmith, and Binhua Lin
Incommensurate phases of a supported nanoparticle film subjected to uniaxial compression
PNAS 110 (3), 824-831 (2013).  Author affiliations:  aJames Franck Institute, bCenter for Advanced Radiation Sources, and cDepartment of Chemistry and Institute for Biophysical Dynamics, University of Chicago; and dDepartment of Physics, University of Wisconsin-Madison.