Nanoemulsions Prepared by a Two-Step Low-Energy Process

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Abstract

Asimple low-energy two-step dilution process has been applied in oil/surfactant/water systems with pentaoxyethylene
lauryl ether (C12E5), dodecyldimethylammonium bromide, sodium bis(2-ethylhexyl)sulfosuccinate, sodium n-dodecyl
sulfate-pentanol, and hexadecyltrimethylammonium bromide-pentanol. Appropriate formulations were chosen for
the concentrate to be diluted with water to generate oil-in-water (O/W) emulsions or nanoemulsions. For the system
of decane/C12E5/water, bluish, transparent nanoemulsions having droplet radii of the order of 15 nm were formed,
only when the initial concentrate was a bicontinuous microemulsion, whereas opaque emulsions were generated if
the concentrate began in an emulsion-phase region. Nanoemulsions generated in the system decane/C12E5/water have
been investigated both by dynamic light scattering (DLS) and contrast-variation small-angle neutron scattering (SANS).
The SANS profiles show that nanodroplets exist as spherical core-shell (decane-C12E5) particles, which suffer
essentially no structural change on dilution with water, at least for volume fractions φ down to 0.060. These results
suggest that the nanoemulsion droplet structure is mainly controlled by the phase behavior of the initial concentrate
and is largely independent of dilution. A discrepancy between apparent nanoemulsion droplet sizes was observed by
comparing DLS and SANS data, which is consistent with long-range droplet interactions occurring outside of the
SANS sensitivity range. These combined phase behavior, SANS, and DLS results suggest a different reason for the
stability/instability of nanoemulsions compared with earlier studies, and here it is proposed that a general mechanism
for nanoemulsion formation is homogeneous nucleation of oil droplets during the emulsification
Original languageEnglish
Pages (from-to)6092-6099
Number of pages8
JournalLangmuir
Volume24
Publication statusPublished - 2008

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