Emulsion stabilisation by complexes of oppositely charged synthetic polyelectrolytes

Abstract

We investigate the possibility of stabilising oil-water emulsions from the polyelectrolyte complexes (PEC) obtained in mixtures of a strong cationic polyelectrolyte (poly(diallyldimethylammonium chloride), PDADMAC) and a weak anionic one (poly(acrylic acid)sodium salt, PAANa). Unlike other previous work however, both polyelectrolytes (PEL) are chosen as they are completely water-soluble and possess no surface activity when present alone over nearly all the pH range. In water, the effects of PEL concentration, PEL mixing ratio and pH on the formation of PEC are studied in detail. At low pH where the anionic PEL is uncharged, complex coacervation occurs in which droplets rich in both polymers are dispersed in water. At intermediate pH, the PEC comprise a mixture of coacervate droplets and solid particles. At high pH where the anionic PEL is significantly charged, only complex coacervation is observed. On addition of dodecane followed by homogenisation, no stable emulsions arose from dispersions containing solid particle PEC due to either the large precursor particle aggregates or their inherent hydrophilicity. By contrast, oil-in-water emulsions stable to coalescence could be prepared from coacervate dispersions. We discuss the feasibility of the coacervate phase spreading at the oil-water interface in terms of the relevant spreading coefficients and compare the predictions with experiment for a range of oils. We encounter oils whose drops become engulfed by the coacervate phase as well as oils where no engulfing occurs.

Emulsions Stabilized with Polyelectrolyte Complexes Prepared from a Mixture of a Weak and a Strong Polyelectrolyte

“…The interface of disperse drops was found to be sparsely covered by PEC particles at high ϕo. Combining the conclusions reported here with those from previous studies, 37,38 we put forward some general rules of behaviour which will help to understand emulsions stabilised by polyelectrolyte complexes prepared from non-surface-active synthetic polyelectrolytes.…”

Capsules from Pickering emulsion templates

“…In this liquid-liquid type of phase separation, which occurs when the interaction between the two polyelectrolytes is weak, liquid droplets concentrated in the two polymers are dispersed within an aqueous continuous phase. The use of coacervate droplets from synthetic non-surface-active polyelectrolytes to stabilise o/w emulsions was reported recently [54]. In ref.…”

Catalysis in Pickering emulsions

“…While typical Pickering emulsion stabilizers are hard particles (mainly from inorganic sources such as silica), some emulsions have been stabilized with soft particles like microgels or from polyelectrolyte complexes. [94][95][96][97] Only a few examples of catalysis in Pickering emulsions stabilized by microgel/nanogel particles or a mixture of microgels (soft) and solid particles (hard) are reported. [98][99][100][101] Microgels are soft cross-linked polymer particles that are able to adsorb at liquid-liquid interfaces and swell or contract under the action of an external stimulus.…”