Surface charge effects on solvation across liquid/liquid and model liquid/liquid interfaces

Area of Science:

• Physical Chemistry
• Interface Science
• Spectroscopy

Background:

• Understanding solvation at liquid interfaces is crucial for chemical processes.
• Surface charge significantly influences interfacial properties.
• Novel molecular probes are needed to dissect complex interfacial environments.

Purpose of the Study:

• To investigate interfacial solvation dynamics using solvatochromic surfactants.
• To explore the impact of surface charge on solvation at liquid/liquid and liquid/vapor interfaces.
• To develop and utilize "molecular rulers" for probing interfacial structure.

Main Methods:

• Resonance enhanced second harmonic generation (SHG) spectroscopy.
• Synthesis and application of novel solvatochromic surfactants ("molecular rulers") with variable alkyl spacer lengths.
• Probing water/cyclohexane interfaces and aqueous liquid/vapor interfaces with 1-octanol monolayers.

Main Results:

• Cationic and anionic surfactants exhibit distinct solvation behaviors across a water/cyclohexane interface.
• Anionic surfactant solvation smoothly transitions from aqueous to organic limits with increasing spacer length.
• Molecular ruler systems at liquid/vapor interfaces qualitatively mimic bulk interfaces and are easier to assemble.
• Headgroup of cationic surfactants alters chromophore electronic structure, not the nonpolar environment.

Conclusions:

• Solvation at charged interfaces is highly dependent on surfactant type (cationic vs. anionic).
• Molecular rulers provide a versatile tool for studying interfacial solvation and structure.
• Surface charge plays a critical role in modulating the interfacial environment.