Mesophase separation in polyelectrolyte-mixed micelle coacervates

Mesophase separation has been identified in a polycation/anionic-nonionic mixed micelle system formed by the coacervation of poly(diallyldimethylammoniumchloride)/sodium dodecylsulfate-Triton X-100 in 0.40 M NaCl. The resultant dense, optically clear fluid was studied by turbidity, dynamic light scattering (DLS), and rheology. The presence of two diffusion modes in DLS points to microscopic heterogeneity: coexistence of micelle-rich (dense) domains with micelle-poor (dilute) domains. With an increase in temperature above 20 °C, the turbidity rises rapidly along with the intensity of the slow mode. The concomitant decrease in the diffusivity of the slow mode signals an increase in the effective viscosity of the dense domain. With further increase in temperature, dramatic shear thinning is observed, and finally, macroscopic phase separation can be identified by centrifugation. At a temperature near that for quiescent phase separation, we observe shear-induced phase separation. We propose a mechanism to explain the connection between temperature- and shear-induced mesophase separation

Effects of protein-polyelectrolyte affinity and polyelectrolyte molecular weight on dynamic properties of bovine serum albumin-poly(diallyldimethylammonium chloride) coacervates

Bovine serum albumin (BSA) and poly(diallyldimethylammonium chloride) (PDADMAC) spontaneously form, over a range of ionic strength I and pH, dense fluids rich in both macroions. To study their nanostructure, these coacervates were prepared at low I and high pH (strong interaction) or at high I and lower pH (weaker interaction), with polymer MWs ranging from 90K to 700K, and then examined by dynamic light scattering (DLS) and rheology. DLS shows a dominant and surprisingly fast protein diffusional mode independent of polymer MW; accompanied by robust slow modes, slower by 1-2 orders of magnitude, which are also insensitive to MW and are present regardless of I, pH, and sample aging. High MW sensitivity was observed by rheology for the terminal time (order of milliseconds), which increased as well with the strength of polyelectrolyte-protein interaction. Viscoelastic behavior also indicated a tenuous network, solidlike at low strain but re-forming after breakage by shear. Two models, both of which have strengths and defects, are put forward: (I) macroion-rich domains dispersed in a continuum of macroion-poor domains near the percolation limit and (II) a semidilute solution of PDADMAC chains with interchain friction modulated by transient BSA-PDADMAC association

Dilution induced coacervation in polyelectrolyte-micelle and polyelectrolyte-protein systems

“Self-suppression”, the instability of complex coacervates at high concentration, is well-known for polycation–polyanion systems, but the transient nature of those complexes impedes development of a convincing model.</p

Higher order association in polyelectrolyte-micelle complexes

Langmuir681422-142

Coexistence of spheres and rods in micellar solution of dodecyldimethylamine oxide

Micelles of dimethyldodecylamine oxide (DMDAO) are known to exhibit sphere-to-rod transitions as a function of pH and ionic strength. Long micelles are stabilized at pH corresponding to half-protonation, because hydrogen bonding between nonionic and protonated monomers yields an effectively double-tailed monomer whose geometry favors cylindrical growth. Dynamic light scattering (DLS) was used to follow particle size distribution as a function of pH, ionic strength (I), and surfactant concentration. The key finding was the coexistence of spherical micelles with rodlike ones at 4 0.2 M. These observations have been verified by varying the algorithm used for the Laplace transformation of the autocorrelation function and also with different DLS systems. The effect of surfactant concentration was used to confirm the absence of any influence of micelle - micelle interaction on the dynamics of diffusion. A molecular level self-consistent field analysis of finite size rodlike micelles confirms the idea that the endcaps are swollen with respect to the cylindrical part. The theoretical results support the coexistence of rods and spherical micelles, i.e., the existence of gaps in the size distribution of wormlike micelles. The cause of coexistence has been explained in terms of the instability of dumbbell-like micelles with domains of negative curvature (neck). The endcap energy is shown to be given (in first order) by the grand potential of spherical micelles that coexist with the wormlike micelles