H. Kunieda et al., THE EFFECT OF MIXING OF SURFACTANTS ON SOLUBILIZATION IN A MICROEMULSION SYSTEM, Journal of colloid and interface science, 170(1), 1995, pp. 78-84
The effect of mixing homogeneous polyethylene glycol alkyl ethers (R(m
)EO(n)) on their maximum solubilizing power was investigated at the hy
drophile-lipophile balance (HLB) temperature at which a microemulsion
(surfactant) containing equal weights of water and oil is one phase of
a three-phase body. The solubilization was compared at a fixed temper
ature equal to the HLB temperature for a single R(12)EO(5) system. It
was found that the minimum weight fraction of surfactant required to s
olubilize equal weights of water and oil into a single phase (X(b)) is
decreased by mixing R(12)EO(2) and R(12)EO(8) or R(14)EO(5) and R(10)
EO(5). However, X(b) for the R(12)OH-R(12)EO(8) system is larger than
for the R(12)EO(2)-R(12)EO(8) system. Namely, the solubilization appar
ently reaches its maximum in a mixed surfactant system in which the hy
drophilic-lipophilic properties of the surfactants are not very differ
ent. Nonionic surfactant is mainly distributed between oil microdomain
s and the interface between oil and water microdomains inside the micr
oemulsion phase, Assuming that the monomeric solubility of each surfac
tant component in oil is the same as in the oil microdomain of the mic
roemulsion, the weight fraction of each surfactant at the interface in
the microemulsion (C or C-i) was obtained. C or C-1 + C-2 indicates t
he real solubilizing power, and it is dramatically decreased when surf
actants are mixed. The more the HLBs of the surfactants are separated,
the more the real solubilizing power is increased, It was also found
that the mixing ratio of surfactants at the water-oil interface inside
the microemulsion phase is directly related to the HLB temperature. (
C) 1995 Academic Press, Inc.