Measuring the Intermolecular Interactions in Molecular Patterns on Surfaces Using Microscopy

Abstract

Understanding the formation and disassembly of molecular adlayer patterns on surfaces at the molecular level has high fundamental and applied importance. With the combination of atomic force micrographs and statistical analysis of adlayers annealed to different temperatures of two similar molecules (trimesic acid and benzene-1,3,5-tricarboxaldehyde), the enthalpy to disassembly (Δdis H) molecules from a molecular pattern on a surface is quantitatively determined. The difference in the intermolecular interaction in their molecular patterns could be directly quantified from Δdis H. We also observed that Δdis H decreases with decreasing initial absolute coverage of the adlayer, which turns out to be related to the measure of the average number of intermolecular interactions per molecule in a given adlayer pattern. By determining the change in entropy and Gibb’s free energy, we could predict precisely the threshold temperature for the disassembly of the molecular patterns.

Reactive Force Field-Based Molecular Dynamics Simulations on the Thermal Stability of Trimesic Acid on Graphene: Implications for the Design of Supramolecular Networks

“…The fact that the directional hydrogen bonding has a destabilizing effect for the close-packed motif is further supported by the experimental observation of a stable closepacked structure for TCA molecules, 22,55 which have aldehyde groups in the 1, 3, and 5 positions of the central benzene ring and consequently have weaker and nondirectional intermolecular interactions. 55 In our calculations, we have not considered solvent effects. The solvent-induced polymorphism is well documented in the literature, and the general trend is that short-chain fatty acids yield the more densely packed structures, whereas the honeycomb motif emerges for fatty acids with long chains.…”

“…Comparing Table a,b, it can be appreciated that the interaction energies between the TMA molecules account for half of the formation energy of the network on the graphene surface. By performing AFM measurements as a function of temperature, Mishra et al calculated the energy required to break all of the intermolecular interactions and to disassemble the honeycomb pattern on the surface . They obtained a disassembly enthalpy of 25.4 kcal/mol per TMA molecule.…”

“…Mishra et al 55 investigated the disassembly of TMA patterns with the honeycomb structure as a function of annealing temperatures at the graphite/air interface using atomic force microscopy (AFM). They observed that there is a threshold temperature for the disassembly of the honeycomb pattern, and they remark that below this temperature, the TMA patterns remain stable.…”

“…Mishra et al concluded that both diffusion and desorption occur simultaneously upon annealing the honeycomb domains of TMA molecules, in agreement with our MD simulations that show these processes. The threshold temperature observed in Figure a is higher than the value observed experimentally (≈370 K), and this is related to the much higher heating rate in our MD simulations and to the fact that we considered a perfect TMA network adlayer with no defects and no edges.…”

“…By performing AFM measurements as a function of temperature, Mishra et al calculated the energy required to break all of the intermolecular interactions and to disassemble the honeycomb pattern on the surface. 55 They obtained a disassembly enthalpy of 25.4 kcal/mol per TMA molecule. Our calculated interaction energies correspond to the reverse process of disassembly.…”