1. Aqueous Solution Microdroplet
Fundamental Studies on the Interfacial Properties of Individual Aqueous Microdroplets in Hydrocarbons Sunghee Lee, Department of Chemistry, Iona College, New Rochelle, NY 10801
Visual evidence of surfactant monolayer at the water-oil interface: Aqueous solute morphology as proxy
Enhanced understanding of the nature of surfactant monolayer and its interfacial structure at the water-oil interface is critical for designing novel functional droplets employed in the food, pharmaceutical, and petroleum industries. In our approach, surfactant packing at the liquid-liquid interface is probed via study of the interplay of incipient crystal lattices of known structure with interfacial amphiphiles. In particular, we have deduced packing parameters for a cationic surfactant (octadecylamine) assembled at an aqueous microdroplet phase containing a crystallizable polyanionic solute of known crystal structure (K3Fe(CN)6). The high charge-size ratio of the hexacyanoferrate anion was found to interact strongly with the cationic headgroups of the surfactant (pKa=10) as evidenced by the induction of euhedral crystal morphology in the presence of submillimolar quantities of surfactant in the oil phase surrounding the microdroplet. Only in the presence of a threshold minimum concentration of surfactant was this effect seen, indicative of the quantity of surfactant molecules necessary for an ordered monolayer. Traditional studies of surfactant packing have been via surface pressure studies on Langmuir monolayers at the air-water interface, but considerably fewer such studies at the oil-water interface.
--> This opens up possibility of probing the interplay between the presence of surfactant and hydrocarbon hydrate crystals at the water-air interface.
Salt nucleation is a prove that can sense minor structural changes of long-chain amphiphilic amines at the water-oil interface.
We have provided evidence that long-chain amphiphilic amines aggregate at the oil-water interface. Salt nucleation is a prove that can sense minor structural changes of such aggregates in the organic environment.
This opens up possibility of probing the interplay between the presence of surfactant and hydrocarbon hydrate crystals at the water-air interface.
Other notable evidence from these studies that indirectly support the nature of the surfactant monolayer at the level of single droplet include:
Variation of onset crystallization concentration as evidence of the recognition of monolayer arrangement at the interface
Variation of water droplet dissolution kinetics
Monolayer disruption upon added intercalant
K3Fe(CN)6
Aqueous Solution Microdroplet
Oil Phase
Surfactant
with 0.01% fatty amine
with 0.05% fatty amine