Amphiphile Blockcopolymere als "Efficiency Booster" für Tenside: Entdeckung und Aufklärung des Effektes

Britta Jakobs, May 2001

It was found and reported for the first time that polymers of the type poly(ethylene-propylen)-co-poly(ethyleneoxide) added in small amounts to conventional microemulsions cause an enormous increase of the efficiency, i.e. solubilization capacity, of surfactants [JAKOBS et al., Langmuir 15, 6707 (1999)]. The effect was called efficiency boosting and is the main subject of this work. Concomitantly with the boosting it is observed that the interfacial tension between the water-rich and the oil-rich phase, which is already ultra-low in microemulsions, is reduced even more. At the same time, the length scale of the microstructure is increased up to orders of magnitude typical for emulsions. The phase inversion temperature of the system is not (balanced polymers) or only marginally affected (unbalanced polymers). The magnitude of the boosting effect depends somewhat on the overall molar mass of the polymers but only weakly on the relative block sizes. The appearance of the lamellar phase can be tuned by varying the combination of the surfactants and polymers used. Small angle neutron scattering (SANS) measurements using a contrast variation technique prove that the polymer decorates the surfactant membrane uniformly in a way that the hydrophilic or hydrophobic block, respectively, extends as a mushroom into the water or oil sub-phase. Further investigations with variation of both the polar and the non-polar solvent as well as the surfactant and the amphiphilic polymer provide evidence that the effects described above can be found in a large variety of pure and technical grade microemulsion systems and thus seem to be based on a common mechanism. An explanation for the effect based on the variation of membrane curvature elasticity by the amphiphilic block copolymer seems to capture the essential features.