Mechanism of Ostwald Ripening in 2D Physisorbed Assemblies at Molecular Time and Length Scale by Molecular Dynamics Simulations

Abstract

Ostwald ripening can improve the long-range order of self-assembled monolayers by the growth of large domains and disassembly of smaller ones. Here, coarse-grained molecular dynamics simulations are used to study the dynamics of the stable assembly and the coarsening of defects of physisorbed monolayers of long-chain functionalized alkanes. Our results show that the partial desorption from the surface of one or more adsorbent molecules is the essential process that allows other adsorbent molecules to rearrange on the surface and thereby improve alignment. We also show that the ripening process is faster at higher temperature because the rate of partial desorption is higher.

Nucleation Mechanisms of Self-Assembled Physisorbed Monolayers on Graphite

“…Most of the final structure is stable and just a small fraction, on the edges of the flake, remains dynamic. On much longer time-scales, remaining defects heal; the mechanisms of the healing process are the subject of a recent study and are not discussed here.…”

“…Most of the final structure is stable and just a small fraction, on the edges of the flake, remains dynamic. On much longer time-scales, remaining defects heal; the mechanisms of the healing process are the subject of a recent study 40 and are not discussed here. The self-assembly process is stochastic in natureit is difficult to create a clear image of the process from a single trajectory, but after several independent self-assembly simulations, clear patterns characterizing the mechanism can be observed.…”

“…51 Mechanisms to heal such defects are discussed elsewhere. 40 At the lower temperature, there is no transition from an unorganized liquid-like phase to a solid phase, and most of the molecules are ordered (Figure 3b). In fitting the nucleation−elongation model (shown in Figure 3c), we assumed that α is the same as for self-assembly at high temperature; i.e., the maximum amount of molecules which can adsorb does not change with temperature.…”

“…Previous work by us on the physisorbed monolayers revealed that partial desorption of the alkanes is closely linked to the rearrangement of molecules on a saturated surface and that the time scales for these rearrangements are accessible by our model. 40…”

The Martini Model in Materials Science

“…Other studies have investigated the self-assembly and self-organization of various long-chain (functionalized) alkanes on graphite (Figure 13). [74,256,257] The Martini simulations performed by Piskorz et al provided a microscopic view on the ad-sorption and subsequent rearrangement of alkanes on the surface to form long-range ordered lamellar structures (Figure 13). The assembly of porphyrin nanorings on graphite has also been explored [258].…”