No abstract

Turbidity, dynamic light scattering, and electrophoretic mobility were used to study the effects of added salt on coacervation in the system composed of the strong cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) and oppositely charged mixed micelles of Triton X-100 (TX100) and sodium dodecyl sulfate (SDS). The phase behavior in the range of ionic strengths from 0.05 to 0.60 M includes regimes of soluble complex formation, coacervation, and precipitation. The corresponding phase boundaries are determined from differential turbidity curves. The shift of the phase boundaries to higher ratios of SDS:TX100 with increase in salt concentration is explained on the basis of electrostatic screening. The width of the coacervation region is found to increase with ionic strength. These observations are consistent with previous reports of the “salt suppression” and “salt enhancement” of coacervation. In the coacervation region, the electrophoretic mobility is found to be close to zero. At higher and lower ionic strengths, soluble complexes are positively or negatively charged, respectively. It is suggested that the principal factor governing coacervation in this system is electroneutrality of the polyion−micelle complex which in turn depends on the charge and number of bound micelles.

The effects of micelle charge density, polymer molecular weight, and polymer-to-surfactant ratio on coacervation were studied by turbidity, dynamic light scattering, and electrophoretic mobility in the system composed of the strong cationic polymer poly(diallyldimethylammonium chloride) (PDADMAC) and oppositely charged mixed micelles of Triton X-100 (TX100) and sodium dodecyl sulfate (SDS). Phase boundaries in the range of SDS mole fraction from 0.30 to 0.50 and in the range of polymer molecular weight from 8.2 × 10 3 to 4.28 × 10 5 were obtained, and coacervate volume fraction as a function of polymer molecular weight was subsequently determined. Three-dimensional phase boundaries were used to represent the effects on coacervation of micelle surface charge density, polymer molecular weight, and PDADMAC-to-SDS ratio. The coacervation region is seen to increase with micelle surface charge density and polymer molecular weight (MW). Both higher and lower polyelectrolyte-to-surfactant ratio can suppress coacervation. An increase in MW reduces the micelle charge required for coacervation and also increases coacervate volume fraction. Coacervation is found to occur when the following conditions are satisfied: the electrophoretic mobility is close to zero, and the size of polyelectrolyte-micelle complex is at least about 45 nm.

No abstract

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.