Influence of Multidirectional Interactions on Domain Size and Shape of 2-D Molecular Assemblies

Abstract

The effect of molecule-molecule interactions on the size and shape of two-dimensional (2-D) ordering domains was investigated using scanning tunneling microscopy (STM) at the liquid/solid interface. Synthesized alkoxybenzene derivatives bearing amide group tend to form very large domains of 2-D orderings (>0.25 μm), whereas the domain size of corresponding urea derivatives was significantly small in the same condition. The quantitative analysis of the concentration dependence of surface coverage using a nucleation-elongation model suggests that the replacement of amide functionality by urea increased the equilibrium constant of the nucleation process of 2-D self-assembly, which is a key factor for the domain size at the liquid/solid interface. Interestingly, the STM observation revealed that a slight difference of molecular structure influences the shape of 2-D ordering domains, and needle-shaped domains with large aspect ratio around 10 were observed by tuning molecule-molecule intramolecular interactions in 2-D self-assembly formed at a liquid/graphite interface.

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

“…Experimental studies of the molecular details of the coarsening process by STM are limited by its spatial and temporal resolution, as well as by potentially strong interactions between the probe and the adsorbent. 10…”

“…Note that the term “coarsening” in the context of domain formation and growth refers to the appearance of large, long-range ordered domains. Experimental studies of the molecular details of the coarsening process by STM are limited by its spatial and temporal resolution, as well as by potentially strong interactions between the probe and the adsorbent …”

Nucleation Mechanisms of Self-Assembled Physisorbed Monolayers on Graphite

“…Despite the fact that clear nucleation events have not been observed in our simulations, the transition from an unordered to an ordered assembly on the surface can be described using the nucleation-elongation model for 2D self-assemblies at liquid/solid interface, developed by Matsuda et al − (Figure c). Our modified version of this model (eqs and ) assumes, that the assembly process can be described by two equilibrium constants: (a) a nucleation constant K n between an adsorbent molecule in solution or on the surface in an unordered state (denoted A 1 unord ) and a free surface adsorption site ( S ) on the one hand and an ordered state ( A 1 ord ) on the other hand (a molecule is in an ordered state when it has two close neighbors with the same orientation, by which we mean it can be parallel or antiparallel; see Supporting Information for details), which acts as a nucleus on the surface; and (b) an elongation constant K e between an adsorbent molecule in an unordered state and ordered clusters of any size ( A n ord ) adsorbed on the surface (note that, in the original model of Matsuda et al, this equilibrium is only between monomers in solvent and clusters on the surface): Using the steady-state approximation, an expression for the surface coverage of ordered molecules, θ, as a function of bulk concentration of adsorbent, c t , can be derived (a detailed derivation can be found in the Supporting Information): Here σ is the degree of cooperativity defined as the ratio between the two equilibrium constants for nucleation and elongation, σ = K n / K e , and α is the maximum concentration of ordered molecules on the graphite surface.…”

“…A well-accepted model to describe the formation of SAMNs is based on nucleation and growth . Matsuda et al − have proposed that similar formation mechanisms as in supramolecular polymerization are present for SAMNs: the isodesmic mechanism, in which molecules as they adsorb to the surface join ordered domains, and the cooperative mechanism, in which a certain concentration of molecules has to be present on the surface before ordered domains can be formed. Depending on the chemical nature of the molecular building block the formation of the assembly can follow one of these paths .…”

Photoresponsive supramolecular self-assemblies at the liquid/solid interface

“…Inspired by cooperative supramolecular polymerization in solution [108,109], our group has recently developed a model of the equilibrium at the liquid/solid interface and used this model to investigate the formation of 2D molecular orderings [100,102,106,107]. The model considers two different equilibrium constants, the nucleation (Kn) and elongation (Ke) constants, for the first nucleation step and the subsequent elongation steps described in equation 1, respectively.…”