Glycerol-induced swollen lamellar phases with siloxane copolymers.
Phase behavior is established for a block copolymer polyethyleneoxide-b-dimethylsiloxane-polyethylenoxide (EO)(15)-(PDMS)(15)-(EO)(15) (IM-22) a in glycerol/water mixed solvent. In water alone, the block copolymer forms biphasic micellar/lamellar (L(1)/L(alpha)) systems over the range 10-70 wt%, with single L(alpha)-phases between 70-90 wt%. Strong solvent effects on the phase behavior were noted. For example, using a mixed 60:40 vol% glycerol/water solvent, the single L(alpha)-phase region appears at much lower concentrations, only 20 wt% IM-22, as compared to the biphasic L(1)/L(alpha) system observed in water alone. This interesting observation of L(alpha)-phase swelling on addition of glycerol may be explained by a decrease in attraction between the bilayers, as it is also found that in this mixed glycerol/water solvent there is a close refractive index matching with IM-22. Rheological measurements show the L(alpha)-phases with added glycerol have low shear moduli. The influence of added ionic surfactant sodium dodecylsulfate (SDS) on these swollen IM-22 L(alpha)-phases was studied. Small-angle X-ray scattering (SAXS) indicated the interlamellar distance d remains essentially constant up to 3 mM SDS, and then decreases with increasing SDS content. This weak effect is consistent with the fact that the L(alpha)-phases are most swollen when the mixed solvent contains 60 vol% glycerol. The results suggest that glycerol/water solvent mixtures can be used to tune the refractive index of the background solvent, modifying DLVO-type interactions, and causing significant effects on the phase stability of simple block-copolymer systems.
Zou
Aihua
A
University of Bayreuth, BZKG, Bayreuth 95448, Germany. aihuazou@hotmail.com
Hoffmann
Heinz
H
Eastoe
Julian
J
Glatter
Otto
O
D055598:Chemical Phenomena; D002627:Chemistry, Physical; D004129:Dimethylpolysiloxanes / Q000737:chemistry*; D005990:Glycerol / Q000737:chemistry*; D008823:Micelles; D011092:Polyethylene Glycols / Q000737:chemistry*; D012212:Rheology; D053838:Scattering, Small Angle; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry; D012997:Solvents / Q000737:chemistry; D014867:Water / Q000737:chemistry; D014961:X-Ray Diffraction
D004129:Dimethylpolysiloxanes; D008823:Micelles; D012997:Solvents; D014867:Water; D012967:Sodium Dodecyl Sulfate; D011092:Polyethylene Glycols; D005990:Glycerol