Quantifying the Cooperative Process of Molecular Self-Assembly on Surfaces: A Case Study of Isophthalic Acids

Abstract

Molecular self-assembly, a promising strategy for modifying surfaces on the nanometer scale, is essential for developing functional materials in electronics, catalysis, or two-dimensional (2D) crystal engineering. In this work, we are shifting attention to the physical chemistry of the process at a molecular level through a study of the effect of concentration on the overall process of self-assembled molecular network formation using scanning tunneling microscopy. The overarching idea is to correlate experimental results with analytical thermodynamic models to improve the understanding of supramolecular chemistry in two dimensions by obtaining quantitative data. For this purpose, a series of isophthalic acids have been chosen as a model system. The effect of the concentration on the adsorption behavior, focusing on the surface coverage, has been evaluated at the nanoscale. Our results confirm the existence of a critical concentration above which self-assembly occurs and that a change in the molecular structure (the length of the alkyl chain) has a remarkable impact on the value of this critical threshold. Finally, we report highly cooperative behavior in studied systems, which presents one of the rare examples of quantitative measurement of cooperative phenomena at the liquid/solid interface.