Phase inversion of polyacrylamide‐based inverse‐emulsions: Influence of inverting‐surfactant type and concentration

The phase inversion of polymeric water‐in‐oil emulsions has been systematically studied by employing nonylphenol and alcohol ethoxylates with various chemistries as well as physical chemical characteristics. A combination of thermodynamics, phase diagrams, and rheometry were used to investigate the behavior of the inverting surfactants as well as the inverted, acrylamide‐based, cationic emulsions. Polymeric inverse‐emulsions containing the inverting surfactant showed no evidence of low‐shear thinning, though they did thin as hydrodynamic forces increased (0.01 to 100 s^?1) prior to reaching a chemistry‐ and concentration‐independent plateau, as is typical for emulsions. The viscosity of emulsions containing inverting surfactants reached a minimum at 1.2% of the “emulsion breaker”. The efficiency of inversion was optimized at 2 wt % of nonylphenols, expressed as a percentage of the total emulsion mass, and increased with the degree of ethoxylation. Interestingly, the viscosity of the polymer inverted in water was maximized at an inverting‐surfactant level corresponding to the CMC of the pure surfactant in water. The alcohol ethoxylates required a higher concentration for inversion (3 wt %), though they provided a higher ultimate inverse viscosity of the polymeric emulsion in water. Therefore, while the inversion process was less efficient with alcohol ethoxylates, the ultimate dilution solution properties of the polyelectrolytes liberated were improved relative to the nonylphenols. Overall, the process of adding a water‐in‐oil emulsion, containing an emulsion breaker, to an excess of water involves a catastrophic inversion mechanism. To be effective under such circumstances, an inverting surfactant should have a partition coefficient between the aqueous an organic phases greatly exceeding unity as well as a hydrophilic–lipophilic balance (HLB) above 12. Effectiveness increases linearly with the partition coefficient. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3567–3584, 2007