Food-grade Microemulsions As Nano-scale Controlled Delivery Vehicles - Food and Industrial Bioproducts and Bioprocessing - page 151

Oil (C)

0

100

10

90

20

80

30

70

40

60

50

50

60

40

70

30

X

80

o 20

90

10

100

0

0 0 0 0 0 0 0 0 0 0 0

Water (A) Surfactant (B)

Figure 5.4 Putative ternary phase diagram.

applying the same logic, the proportions of the surfactant (B) (10%) and oil phases (C) (20%)
can be determined. Any point along the axes consists of two components only.
A key property dictating the functionality of microemulsions will be whether these can
be infinitely diluted by the continuous phase without loss of structure. Such fully dilutable
(“U-type”) microemulsions yield large isotropic regions extending from the oil-rich to
the water-rich apex, without any phase separation (Garti, 2003). Garti and co-workers were
the first to develop dilutable microemulsions, in which the L 2 microemulsions were dilutable
with aqueous phase (Garti et al ., 2005). This was achieved by addition of co-surfactants to
the system, thereby increasing the flexibility of the interface. These dilutable microemulsions
had a high solubilization capacity and could be used for the transport of hydrophobic guest
molecules (nutraceuticals, drugs, etc.), which are normally water insoluble.

5.10.2 Small angle scattering techniques
Small angle scattering techniques, such as SAXS and SANS, are often used to provide
information on microemulsion droplet shape and size (Moulik and Paul, 1998; Garti and
Aserin, 2006). In these methods, the intensity of the light, scattered at low angles, provides
structural information about the scattering species (e.g., oil or water droplets in a microemul-
sion) (Moulik and Paul, 1998). The scattering intensity depends on the scattering length
density of the droplets and the continuous phase (Garti and Aserin, 2006). In both techniques,
there is a sharp change of scattering length density across the amphiphilic film, which
separates the water and oil regions in a microemulsion (Regev et al ., 1996 ).

5.10.2.1 Small angle X-ray scattering

This technique is quite commonly used to characterize microemulsions, providing informa-
tion on domain size and spatial arrangement. Regev and co-workers (1996) characterized
octaethylene glycol mono n -dodecyl ether-dodecane-pentanol-water systems as a fire-resistant