Structural characterization of interfacial n-octanol and 3-octanol using molecular dynamic simulations

Area of Science:

• Physical Chemistry
• Materials Science
• Chemical Engineering

Background:

• Understanding liquid/liquid interfaces is crucial for various chemical processes.
• Molecular simulations provide atomistic insights into interfacial phenomena.
• Octanol isomers exhibit different behaviors at interfaces due to their structures.

Purpose of the Study:

• To investigate the atomistic structure of structurally isomeric octanol/water and octanol/vapor interfaces.
• To compare the interfacial properties of n-octanol and 3-octanol.
• To probe the influence of molecular topology on interfacial ordering and properties.

Main Methods:

• Molecular dynamics simulations at 298 K.
• Constant pressure equilibration techniques to ensure proper phase separation and interface formation.
• Analysis of density profiles and orientational order parameters.

Main Results:

• Both n-octanol and 3-octanol interfaces exhibit some water molecules within the octanol phase ('wet' interfaces).
• N-octanol interfaces display extended molecular ordering (several layers) driven by hydrogen bonding between hydroxyl groups and water, creating hydrophilic/hydrophobic layering and an oscillating dielectric response.
• 3-octanol interfaces show more localized ordering (1-2 layers) with a single carbon-rich layer due to its different molecular topology.
• Both isomers roughen the water interface compared to the water/vapor interface.
• Wet octanol phases reach bulk properties faster than dry octanol/vapor interfaces.

Conclusions:

• The molecular topology of octanol isomers significantly impacts interfacial structure and properties.
• N-octanol's linear structure promotes extensive interfacial ordering through hydrogen bonding, while 3-octanol's branched structure leads to more confined ordering.
• These findings enhance the understanding of molecular interactions at liquid/liquid interfaces and their dependence on molecular architecture.