Highly hydrophobically modified polyelectrolytes: Field variables to control emulsion type

Highly hydrophobically modified (with n-dodecylamide chain) linear poly(acrylic acid)s (HHMPAAH) and poly(sodium acrylate)s (HHMPAANa) with various degrees of grafting (τ) were synthesized and used as emulsifiers of the n-dodecane/water system. The type of emulsion, oil in water (O/W) or water in oil (W/O), was investigated as a function of the polymer chemical structure (τ, salt or acid form of the copolymer) and aqueous phase electrolyte concentration (NaNO₃). Increasing τ and/or salt concentration was found to favor the formation of inverse emulsions. Direct liquid–liquid dispersions are more likely to form with poly(sodium acrylate)s than with poly(acrylic acid)s. Hence, field variables such as τ, pH and ionic strength are relevant parameters to control emulsion type. Moreover, a balanced polyelectrolyte neither soluble in oil nor in water was synthesized for the first time. With this original emulsifier, the dispersion type was found to change from O/W to W/O with polymer salting out. The work provides convenient model system for fundamental studies of polymer conformation at liquid–liquid interfaces. Received: 31 March 1998 Accepted: 30 April 1998     

Highly hydrophobically modified polyelectrolytes stabilizing macroemulsions: relationship between copolymer structure and emulsion type

The types of emulsions, oil (n-dodecane) in water (O/W) or water in oil (W/O), stabilized with highly hydrophobically grafted linear poly(sodium acrylate)s, were investigated as a function of polymer chemical architecture. Consequently, a large number of macroemulsifiers, covering a wide range of hydrophobicity, were synthesized by changing the degree of grafting (τ), length (n) and type (single- versus twin-tailed) of the hydrophobic moiety. Monovalent salt (NaNO₃) concentration was used as a probe to adjust and hence to estimate the hydrophile-lipophile balance (HLB) of each copolymer. τ, n, type of graft and electrolyte concentration were identified as field parameters to control emulsion type. In general, decreasing either τ or n was found to favor the formation of direct emulsions. Inverse dispersions were preferentially formed with twin-tailed rather than single-tailed copolymers. Moreover, the types of emulsions stabilized with well-balanced polyelectrolytes can be flipped from O/W to W/O with increasing salt concentration. Finally, following the Davies concept, a HLB scale for polymers was created from a comparison with surfactants of nearly identical chemical structure. Received: 15 June 1998 Accepted: 12 August 1998