Nr. Cameron et Dc. Sherrington, NONAQUEOUS HIGH INTERNAL PHASE EMULSIONS - PREPARATION AND STABILITY, Journal of the Chemical Society. Faraday transactions, 92(9), 1996, pp. 1543-1547
Citations number
31
Categorie Soggetti
Chemistry Physical","Physics, Atomic, Molecular & Chemical
Several novel non-aqueous high internal phase emulsions (HIPEs) of pet
roleum ether dispersed in a number of polar organic solvents [formamid
e (FA), N,N'-dimethyl formamide (DMF) and dimethyl sulfoxide (DMSO)I a
s the continuous phase, with internal phase volume ratios ((phi) of 0.
9, have been prepared, employing both polymeric and non-polymeric non-
ionic surfactants. A number of factors have been shown to be important
in determining HIPE stability. First, the nature of the polar organic
phase: the most stable emulsions are formed with formamide. This is a
ttributed to its high polarity and ability to form a water-like hydrog
en-bonded network, however, rationalising the relative performance of
the other polar solvents is more difficult. Second, the interfacial be
haviour of the surfactant employed: interfacial data for aqueous solut
ions in contact with hydrocarbon do not adequately describe surfactant
performance and a much better guide is the hydrophilic-lipophilic bal
ance (HLB) value of the surfactant. Although this may be an empirical
guide to surfactant behaviour, in this context it is useful, indeed ra
ther powerful. The third important parameter is the molecular size or
complexity of the surfactant. Generally, low-molecular-weight surfacta
nts perform poorly, whereas PEO-PPO-PEO block copolymers of appropriat
e HLB value allow the formation of stable HIPEs. The PEO block appears
to be solubilised in the polar solvent and the PPO block in the hydro
carbon. Presumably, each block attempts to form a (separate) random co
il on its own side of the interface. Consequential effects may well in
clude an increase in viscosity and slow desorption kinetics at the int
erface.