화학공학소재연구정보센터
Macromolecules, Vol.28, No.15, 5225-5229, 1995
Laser-Light Scattering Study of a Very Dilute Water/Sodium bis(2-Ethylhexyl)Sulfosuccinate/N-Hexane Microemulsion Stabilized by Poly(N-Isopropylacrylamide)
The "water-in-oil" microemulsion polymerization of (N-isopropylacrylamide) (NIPAM) enabled us to prepare a series of dilute "water/sodium bis(2-ethylhexyl)sulfosuccinate (AOT)/n-hexane" microemulsions with PNIPAM as a stabilizer. A combination of static and dynamic laser light scattering (LLS) was used to study the temperature (T) and dispersed-phase concentration (C) dependence of this series of dilute microemulsions. For a given water/AOT molar ratio of omega = 23, the average hydrodynamic radius (R(h)) of the microemulsion increases with T when C is higher than 0.150 g/mL but decreases when C is similar to 100-fold dilute. In comparison with the H2O/AOT/n-hexane microemulsion wherein no PNIPAM is introduced as a stabilizer, the H2O(PNIPAM)/AOT/n-hexane microemulsion is much more stable in the range of 1.50 x 10(-3) less than or equal to C less than or equal to 7.50 x 10(-3) g/mL. On the basis of a spherical core-shell model, i.e., a water core coated with a layer of AOT, we determined the AOT layer thickness (b) from the difference between the hydrodynamic radius (R(h)) measured in dynamic LLS and the radius of the water core (R(c)) calculated from the mass (M(w)) of the water core obtained in static LLS, i.e., b = R(h) - R(c). The estimate of b similar to 1.1 nm indicates that the water core is covered with only one monolayer of AOT molecules and the AOT molecules stand right on the surface of the water core, which is quite different from our previously reported model for the "oil-in-water" microemulsion, wherein half of the surfactant hydrophobic tail penetrates into the core.