On the Mechanism of Shear-Thinning in Viscous Oppositely Charged Polyelectrolyte Surfactant Complexes (PESCs)

Abstract

Semidilute mixtures of the cationically modified cellulose-based polyelectrolyte JR 400 and the anionic surfactant sodium dodecyl sulfate (SDS) form highly viscous solutions if a slight excess of charges from the polyelectrolyte is present. The reason for this is the formation of mixed rodlike aggregates in which the surfactant cross-links several polyelectrolyte chains. The same solutions also show shear-thinning behavior. In this paper, we use rheoSANS to investigate the structural evolution of the rodlike aggregates under steady shear and thereby elucidate the mechanism of shear-thinning in these viscous oppositely charged polyelectrolyte surfactant complexes.

Charge Modification as a Mechanism for Tunable Properties in Polymer–Surfactant Complexes

“…There have been several studies that have utilised contrast variation SANS to fully elucidate the aggregates formed by oppositely charged cat-HEC polymer and small molecule surfactants, most of which have focused on the cat-HEC polymer JR400 (similar to N = 1.8% in this work) [ 15 , 16 , 17 , 18 , 20 , 23 ]. A mutual conclusion from these investigations have shown that within the PE excess regime (Z > 1), mixed rodlike aggregates are produced with a significantly larger size than the constituent PE.…”

“…Indeed many of the applications that employ oppositely charged polymer–surfactant systems make use of synthetic polymers such as anionic poly(acrylic acid) or cationic poly(diallyldimethylammonium chloride) [ 2 , 5 , 10 , 11 , 12 , 13 ]. However, more recently, polysaccharides have emerged as an important component in commercially formulated products as a result of their biocompatibility, biodegradability, bioadhesivity, and nontoxicity [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. One series of polysaccharide-based polyelectrolytes (PEs) that have received particular attention due to their commercial relevance and interesting rheological properties are cationic hydroxyethyl cellulose (cat-HEC) polymers, in particular, JR400 [ 14 , 15 , 16 , 17 , 18 , 20 , 23 , 25 ].…”

“…However, more recently, polysaccharides have emerged as an important component in commercially formulated products as a result of their biocompatibility, biodegradability, bioadhesivity, and nontoxicity [ 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 ]. One series of polysaccharide-based polyelectrolytes (PEs) that have received particular attention due to their commercial relevance and interesting rheological properties are cationic hydroxyethyl cellulose (cat-HEC) polymers, in particular, JR400 [ 14 , 15 , 16 , 17 , 18 , 20 , 23 , 25 ]. In oppositely charged PE–surfactant complexes, around charge neutrality (where Z = 1), it is common to observe an extended region of precipitate formation, while in the region of excess surfactant ( Z < 1) or PE ( Z > 1), soluble complexes are formed [ 2 , 19 ].…”

“…Through in-depth small-angle neutron scattering (SANS), dynamic light scattering (DLS), and rheological measurements, comprehensive physiochemical characterisation of mixtures containing JR400 and small-molecule surfactants have been carried out [ 15 , 16 , 17 , 18 , 20 , 23 , 25 ]. At sufficiently high PE concentrations (>0.5 wt%), addition of low concentrations of small-molecule surfactants sodium dodecylsulfate (SDS) or sodium dodecylbenzenesulfonate (SDBS) produced viscosity increases up to four orders of magnitude higher than that of the pure PE [ 15 , 17 , 18 , 24 ].…”

Stimuli-responsive polyelectrolyte surfactant complexes for the reversible control of solution viscosity

“…For JR 400/SDS, it was found that the shear-thinning is related to a slight alignment of mixed PE/surfactant aggregates. 65 The zero-shear viscosity ( η 0 ) of the system (see Fig. S2, ESI†), increases by 3 orders of magnitude relative to the pure JR 400 solution when adding 5 mM SDP − ( Z = 2) and the structural relaxation time τ cross seen by oscillatory measurements (see Fig.…”