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Additive perturbed molecular assembly in two-dimensional crystals: differentiating kinetic and thermodynamic pathways
1Department of Chemistry and the Macromolecular Science and Engineering Program, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
Journal of the American Chemical Society
|February 8, 2012
Summary
Researchers observed metastable forms during two-dimensional cocrystal formation, similar to 3D crystallization. Additives can kinetically control or thermodynamically stabilize these intermediate forms, offering pathways to isolate metastable polymorphs.
Area of Science:
- Materials Science
- Crystallography
- Surface Science
Background:
- Cocrystal formation involves coadsorbing multiple components.
- Polymorphism, the ability of a solid material to exist in multiple crystalline forms, is well-documented in 3D crystallization.
- Additive-induced polymorph formation is a known phenomenon in 3D systems.
Purpose of the Study:
- To investigate the formation of metastable two-dimensional (2D) cocrystals.
- To understand the mechanistic role of additives in 2D cocrystal formation and polymorphism.
- To explore pathways for kinetically isolating metastable polymorphs in 2D systems.
Main Methods:
- Scanning tunneling microscopy (STM) was employed to study the adsorption and assembly processes.
- Various adsorbate/additive combinations were tested to observe their effects.
- Analysis focused on distinguishing kinetic versus thermodynamic control of crystal formation.
Main Results:
- A metastable form of 2D cocrystals was observed, analogous to 3D additive-induced polymorphs.
- One additive promoted disordered assembly via kinetic control.
- Another additive thermodynamically stabilized an intermediate form, hindering phase transformation.
Conclusions:
- Additives play a crucial role in controlling the outcome of 2D cocrystal formation.
- Both kinetic and thermodynamic effects of additives can lead to the isolation of metastable phases.
- These findings provide insights into pathways for achieving metastable polymorphs in 2D crystallization, relevant to 3D crystallization processes.
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