Chemistry Reference
In-Depth Information
Chapter 27
Crystallization in Monodisperse Emulsions
with Particles in Size Range 20-200 nm
Malcolm J.W. Povey,
1
Tarek S. Awad,
1
Ran Huo
1
and
Yulong Ding
2
1
PROCTER DEPARTMENT OF FOOD SCIENCE, UNIVERSITY OF
LEEDS, LEEDS LS2 9JT, UK
2
INSTITUTE FOR PARTICLE SCIENCE AND ENGINEERING,
UNIVERSITY OF LEEDS, LEEDS LS2 9JT, UK
27.1 Introduction
A recent search of the literature for papers on crystallization in oil-in-water
emulsions with authors who use the term 'nano' has generated 260 references,
the first one of which appeared in 1992. The earliest papers were associated with
drug delivery and pharmaceuticals. Crystallizing fats were used instead
of liquid oils because the solid fat gives up the drug more slowly, providing
a controlled release mechanism.
1
An important question is how to crystallize
and stabilize the fat. Initially, the emulsions produced were submicron emul-
sions, sometimes called 'mini-emulsions', with sizes invariably much greater
than 100 nm and a nominal size below 1 mm. Usually called 'parenteral'
emulsions,
2
they were designed for injection into the blood stream and were
normally composed of emulsified soybean oil. The small size was achieved by
high-pressure homogenization, and this was necessary to avoid the presence of
large oil droplets that might interfere with blood circulation. Initially these
parenteral emulsions were produced for intravenous feeding and the prefix
'nano' was not used. However, their use as a vector for drug delivery was clear.
By way of background, it is important to emphasize here that, while many
reports can be found of very small particles of surfactant vesicles/micelles
(e.g., fractionated egg phospholipids
2
) or swollen micelles, convincing evidence
for stable oil particles much below
100 nm is thin on the ground. For
example, particles of size below 100 nm may be produced by dissolution of oil
in an organic solvent, followed by dispersion in water; subsequently the oil
phase crystallizes. This process has been used to produce cholesteryl acetate
particles of
B
100 nm;
3
but no reports specify particles much below this sort of
B
399
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