Characterization of complexation and phase behavior of mixed systems of unmodified and hydrophobically modified oppositely charged polyelectrolytes

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

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.

Use of molecular interactions and mesoscopic scale transitions to modulate protein-polysaccharide structures

Mixed protein-polysaccharide structures have found widespread applications in various fields, such as in foods, pharmaceuticals or personal care products. A better understanding and a more precise control over the molecular interactions between the two types of macromolecules leading to an engineering of nanoscale and colloidal building blocks have fueled the design of novel structures with improved functional properties. However, these building blocks often do not constitute the final matrix. Rather, further process operations are used to transform the initially formed structural entities into bulk matrices. Systematic knowledge on the relation between molecular structure design and subsequent mesoscopic scale transitions induced by processing is scarce. This article aims at establishing a connection between these two approaches. Therefore, it reviews not only studies on the underlying molecular interaction phenomena leading to either a segregative or associative phase behavior and nanoscale or colloidal structures, but also looks at the less systematically studied approach of using macroscopic processing operations such as shearing, heating, crosslinking, and concentrating/drying to transform the initially generated structures into bulk matrices. Thereby, a more comprehensive look is taken at the relationship between different influencing factors, namely solvent conditions (i.e. pH, ionic strength), biopolymer characteristics (i.e. type, charge density, mixing ratio, biopolymer concentration), and processing parameters (i.e. temperature, mechanical stresses, pressure) to generate bulk protein-polysaccharide matrices with different morphological features. The need for a combinatorial approach is then demonstrated by reviewing in detail current mixed protein-polysaccharide applications that increasingly make use of this. In the process, open scientific questions that will need to be addressed in the future are highlighted.

Unique multiple soluble-insoluble phase transitions in aqueous two-phase copolymerization of acrylamide and a weakly charged comonomer

A unique phenomenon of multiple soluble-insoluble phase transitions was found in the two-phase copolymerization of acrylamide (AM) and a weakly charged comonomer, N,N-dimethylaminoethyl methacrylate (DMAEMA), in the aqueous solution of poly(ethylene glycol) (PEG). As the DMAEMA molar fraction increased from 0 to 0.30, the insoluble-soluble (I-S) phase transition first appeared and then disappeared. Varying the PEG concentration, the salt concentration, or the pH of reaction mixture, the phase transitions were tuned dependently. The volume fractions and refractive indices of continuous and disperse phases, as well as the viscosity change in the phase transitions were investigated, and the results showed that phase reentrance had occurred in the I-S phase transition. The transitional conversion for the first S-I phase transition increased with the DMAEMA molar fraction, indicating the solubility enhancement of charged polyelectrolytes. The content of DMAEMA in the resulting copolymer first increased and then decreased as the polymerization progressed. Accordingly, the droplet size increased in the two S-I phase transitions and decreased in the I-S phase transition. And it was proved that the copolymers were molecularly solubilized after the I-S phase transition. The multiple soluble-insoluble phase transitions were ascribed to the synergistic effect of polymer concentration, solubility enhancement of charged copolymers, and the salting-out effect of ionic comonomers. A generalized mechanism for the multiple soluble-insoluble phase transitions was proposed, which showed that the effects of polymer concentration were dominant in the two S-I phase transitions, while the effects of solubility enhancement played a key role in the I-S phase transition.