Interaction of oppositely charged surfactants and polyelectrolytes usually leads to formation of surfactant-polyelectrolyte complexes. Surface activity of such complexes depends on the relative concentration and properties of the surfactant/polyelectrolyte pair. Surface active complexes can be used to stabilize emulsions, further used as cores for encapsulation of hydrophobic components, while non-surface active can be utilized as carriers of hydrophilic compounds.
In the present work we consider both experimentally and theoretically adsorption of cationic esterquat surfactants, in the presence of anionic polyelectrolytes (poly(sodium-4-styrene sulfonate (PSS) and sodium alginate (ALG)). We studied derivatives having –O-CO- bond between quaternary amine and hydrophobic tail: N,N,N-trimethyl-2-(dodecanoyloxy)ethaneammonium bromide (DMM-11) and N,N,N-trimethyl-2-(dodecanoyloxy)-1-methylethaneammonium bromide (DMP2M-11)), and derivatives with –CO-O- bond: dodecyloxycarbonyl-methyl-N,N,N-trimethyl ammonium bromide (DMGM-12)), and dodecyloxycarbonyl-1-ethyl-N,N,N-trimethylammonium bromide (DMALM-12)). These compounds are stable in the acidic conditions but in neutral and basic pH undergo hydrolysis resulting in either dodecanoic acid or dodecanol as surface active products. That influences the surfactant – polyelectrolyte interaction and as consequence the surface activity of their mixtures . The extended “surface quasi two-dimensional electrolyte” (STDE) model of ionic surfactant adsorption was applied for the description of hydrolysis influenced surface activity of surfactants and their mixtures with polyelectrolytes. We found that mixtures of DMGM-12 or DMALM-12 surfactants with polyanions exhibit synergistic effect on the surface tension, decreasing with time as the result of hydrolysis, while in the mixtures of DMM-11 or DMP2M-11 surface active complexes do not form.
Acknowledgements: This work was partially financed by NCN project UMO-2011/03/B/STA/01217
ncwarszy@cyf-kr.edu.pl
