Matthias Löffler

Structure characterization of surfactant assisted polymer thickeners by silica nanocasting

The aggregation behavior of the hydrophobically modified polyelectrolytes which act in the enterplay with special surfactant mixtures as a thickener is examined by replication of the different soft matter nanostructures into silica gels. The inorganic solidified replicas can be easily microtomed and analyzed by gas sorption measurements, quantitative small angle X-ray scattering and transmission electron microscopy. The bare hydrophobically modified polyelectrolytes show a very homogeneous structure, free of larger aggregated moieties. In addition, a transition between a weakly- or unaggregated structure and an aggregated structure of the bare copolymer with hydrophobic moieties of ca. 3 nm diameter was found which depends on the degree of hydrophobic substitution, the concentration, and the salt content. The simultaneous presence of surfactant in the polymer solution leads to nanocasting of both spherical (ionic surfactant) and worm-like (zwitterionic surfactant) micelles, which are essentially unperturbed by the incorporate the hydrophobic moieties of the polymer. Optimal thickening efficiency is obtained when each of those micelles is coupled to at least two of the polymers. The resulting sterical demands are best met by the presence of worm-like surfactant micelles.