Formation and stability of nanoemulsion based on Solbrax
For formation of the nanoemulsions, the Solbrax solvent was
selected as oil phase because it has good affinity with crude oil,
since it is basically composed of a mixture of aliphatic hydrocarbon
naphtha extracted and treated by the catalytic hydrocracking
process. This reduces its aromatics content to less than
1%, presenting low toxicity [19]. The ethoxylated surfactant Utrol
L70 was used to stabilize these nanoemulsions [20].
For the compositions containing 5 to 6 wt% oil phase (Solbrax)
and 10 to 12 wt% of surfactant (ULTROL L70) was not necessary to
use any method of high energy, such as high-shear stirring, highpressure
homogenizers and ultrasound generators for preparation
of nanoemulsion [21]. The oil phase concentration was increased
to 7–10 wt% and the surfactant concentration was maintained
(10 and 12 wt%) and for these systems the nanoemulsions were
obtained in the high-pressure homogenizer.
Table 1 shows the composition and size range (between 5 and
20 nm) of nanoemulsions formed and the times they remained
stable. The photo in Fig. 1a shows the transparency of the
nanoemulsion containing 8 wt% Solbrax and 12 wt% surfactant.
This is due to the tiny size of the droplets. In comparison, the
nanoemulsion that lost size stability had a milky appearance.
Fig. 1b shows the nanoemulsion droplet size distribution curves
in the period of 120 days, and with above 90% of sample volume
in the size range between 5 and 20 nm. Fig. 1c shows an optical
micrograph of the same solution