Particle adsorption at the oil-water interface studied with second harmonic generation

Area of Science:

• Physical Chemistry
• Colloid Science
• Surface Science

Background:

• Understanding nanoparticle behavior at interfaces is crucial for applications in materials science and nanotechnology.
• The hexadecane-water interface serves as a model system for studying oil-water interactions.
• Second harmonic generation (SHG) is a sensitive optical technique for probing interfacial properties.

Purpose of the Study:

• To investigate the energetics of polystyrene nanoparticle adsorption at the hexadecane-water interface.
• To utilize SHG as an indicator for monitoring nanoparticle adsorption.
• To elucidate the driving forces behind nanoparticle adsorption at the oil-water interface.

Main Methods:

• Second harmonic generation (SHG) spectroscopy was employed to study nanoparticle adsorption.
• Adsorption free energies were quantified for different types of charged polystyrene nanoparticles.
• The influence of particle charge and interfacial properties was analyzed.

Main Results:

• Nanoparticle adsorption at the hexadecane-water interface was confirmed and quantified using SHG.
• Adsorption free energies for 20 nm polystyrene nanoparticles were determined to be approximately -14.4 to -15.1 kcal mol⁻¹.
• SHG signal changes correlated with the adsorption of both positively and negatively charged nanoparticles.

Conclusions:

• Van der Waals interactions and the "like dissolves like" principle are key drivers for polystyrene nanoparticle adsorption.
• Negatively charged nanoparticles are effectively adsorbed at the negatively charged hexadecane-water interface.
• SHG is a reliable method for detecting and quantifying nanoparticle adsorption at oil-water interfaces.