Solution-growth kinetics and thermodynamics of nanoporous self-assembled molecular monolayers

Abstract

The temperature and concentration dependences of the self-assembly onto graphite from solution of a series of molecular building blocks able to form nanoporous structures are analyzed experimentally by in situ scanning tunneling microscopy. It is shown that the commonly observed coexistence of dense and nanoporous domains results from kinetic blockades rather than a thermodynamic equilibrium. The ripening can be favored by high densities of domain boundaries, which can be obtained by cooling the substrate before the nucleation and growth. Then ripening at higher-temperature yields large defect-free domains of a single structure. This thermodynamically stable structure can be either the dense or the nanoporous one, depending on the tecton concentration in the supernatant solution. A sharp phase transition from dense to honeycomb structures is observed at a critical concentration. This collective phenomenon is explained by introducing interactions between adsorbed molecules in the thermodynamic description of the whole system.

Principles of molecular assemblies leading to molecular nanostructures

“…Thus, it was generally believed that self-assembly at the liquid-solid interface warrants the optimum conditions to achieve equilibrium and hence leads to formation of thermodynamically stable structures. However, there is increasing evidence that some of the two-dimensional molecular networks formed at the liquidsolid interface are in fact kinetically trapped structures and may not represent the minimum energy equilibrated state [46].…”

“…A number of experimental parameters have already been identified that control the appearance of a certain type of polymorph over another. A non-comprehensive list of these parameters includes the type of solvent [23][24][25][26][27][28][29], the concentration of molecules [30][31][32][33][34][35], the type of substrate [36][37][38][39][40][41], the temperature at which the self-assembly takes place [42][43][44][45] and the thermal history of the sample [46]. How these parameters affect the self-assembly of organic building blocks is the subject of this review, with a special focus on the liquid-solid interface.…”

Self-Assembly Behavior of Alkylated Isophthalic Acids Revisited: Concentration in Control and Guest-Induced Phase Transformation

“…By using hydrogen bonding [5][6][7][8] , van der Waals interactions [9][10][11][12] , metal-ligand coordination [13][14][15] or a combination thereof as a molecular 'glue', a multitude of architectures have been successfully engineered both in ultra-high vacuum conditions as well as at a liquid-solid interface. Predicting the specific outcome of network formation based on the molecular building blocks remains a challenge as various experimental factors govern the selfassembly process: solute concentration, 10,[16][17][18][19][20] temperature [21][22][23][24][25] , solvent 26,27 have all been known to influence the 2D crystal formation under ambient conditions.…”

A priori calculations of the free energy of formation from solution of polymorphic self-assembled monolayers

“…5 and 6), has remained prohibitive a priori. Alternatively, model calculations have been useful for identifying key qualitative features (7)(8)(9)(10)(11), whereas some full molecular dynamics simulations of the free energy using empirical force fields have been revealing for SAMs (12)(13)(14)(15) and also for macromolecules (16), and DFT molecular dynamics approaches are appearing (17). A priori computational methods have significant advantages in that they do not require parameterization, they treat interactions both generally and accurately, and, through use of implicit solvation models, they can avoid extensive liquid structure simulations.…”

“…Experimentally testing this hypothesis requires quantitative information (7,8,33), as has been measured, e.g., for codeposition of single SAMs containing mixed porphyrins (40) to reveal that molecules inside SAM phases are not in equilibrium with those in solution. However, only limited data are available concerning relative polymorph propensities.…”