The formulation of stable, low pH, viscous emulsions and gel
formulations with desirable aesthetics and textures is often challenging.
The most commonly used thickeners are synthetic
associative thickeners; these are frequently anionic and hence
are typically incompatible with cationic components, especially
quaternary ammonium salts. They can also be ineffective thickeners
at low pH.
Formulators seeking to modify the rheology of their product
compositions at low pH, especially emulsions, are limited to
choosing between nonionic thickeners (such as nonionic surfactants)
and cationic thickeners. The former are uncharged and
thus are assumed to be less reactive to cationic components
than anionic thickeners, but they tend to inactivate preservatives
and may promote microbial growth.
Moreover, whilst some cationic polymeric rheology modifiers,
such as hydrophobically modified aminoacrylate copolymers,
are available commercially, their rheological properties
are unacceptable or aesthetically unsatisfactory, yielding a
‘lumpy’ texture.