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Amphiphile self-assembly dynamics at the solution-solid interface reveal asymmetry in head/tail desorption
Henry D Castillo1, John M Espinosa-Duran, James R Dobscha
1Department of Chemistry, Indiana University, 800 E. Kirkwood Avenue, Bloomington, Indiana 47405, USA. tait@indiana.edu.
Chemical Communications (Cambridge, England)
|August 8, 2018
Summary
Amphiphilic alkoxybenzonitriles (ABNs) self-assembly on graphite is controlled by concentration and size. Molecular dynamics reveal that desorption, often initiated by alkyl chain detachment, is favored over head group detachment, influencing adsorption dynamics.
Area of Science:
- Surface Science
- Supramolecular Chemistry
- Materials Science
Background:
- Amphiphilic alkoxybenzonitriles (ABNs) are molecules with both water-loving and water-hating parts.
- Understanding how these molecules assemble on surfaces is crucial for designing new materials.
Purpose of the Study:
- To investigate the dynamics of amphiphilic alkoxybenzonitrile (ABN) assembly at the solution/graphite interface.
- To analyze the factors controlling competitive self-assembly between ABNs and alkanoic acid solvents.
Main Methods:
- Scanning Tunneling Microscopy (STM) to visualize molecular assembly.
- Molecular Dynamics (MD) simulations to probe sub-nanosecond dynamics.
- Studying ABNs with varying alkyl chain lengths.
Main Results:
- Competitive self-assembly is governed by ABN concentration and molecular size.
- Key dynamic steps include adsorption, desorption, and on-surface motion at sub-nanosecond timescales.
- Desorption is favored via alkyl chain detachment due to steric hindrance from neighboring molecules.
Conclusions:
- The study reveals an asymmetric desorption-adsorption mechanism for ABNs on graphite.
- Despite strong solvent affinity, the nitrile head group frequently re-adsorbs after detachment.
- Concentration and molecular size are critical parameters for controlling ABN self-assembly dynamics.
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