Gelled polymerizable microemulsions. Part 3 Rheology

Abstract

This is the first report on the rheological properties of oil-gelled polymerizable bicontinuous microemulsions. The polymerizable base system consists of H₂O/NIPAm/BisAm – n-dodecane – C_13/15E₅ (a technical grade n-alkyl polyglycol ether), where NIPAm denotes the monomer N-isopropylacrylamide and BisAm the cross-linker N,N′-methylene bisacrylamide. For the planned polymerization of the aqueous phase a scaffold is needed to preserve the structure of the templating microemulsion during the polymerization. This scaffold is supposed to be a gel, which was formed by adding the gelator 12-hydroxyoctadecanoic acid (12-HOA) to the oil phase of the microemulsion. The influence of the water-to-oil ratio α, of the gelator concentration β, and of the monomer concentration ψ on the rheological behavior of gelled microemulsions has been studied in detail. The most important result of the study at hand is the observation of a transition from a high viscous solution to a gel, i.e. from a transient to a permanent network, with increasing gelator concentration and increasing amount of the oil phase. In other words, it is only under well-defined conditions that an oil-gelled microemulsion is formed.