Insight into dynamics of polyelectrolyte chains in salt-free solutions by laser light scattering and analytical ultracentrifugation

Insights into interaction mechanism between xanthan gum and galactomannan based on density functional theory and rheological properties

To explore the interaction sites and energies of ordered and disordered xanthan gum with locust bean gum (LBG), we prepared xanthan with different conformations and used it to form synergistic complexes with LBG. The interaction strength between xanthan and LBG was analyzed by analog computation using the density functional theory (DFT) method. Furthermore, the viscoelastic changes of the xanthan-LBG complex in different solutions were analyzed to verify the DFT results. The results showed that the ordered xanthan interacted with LBG through the side chains, with an interaction energy (E_Int) of -479.450 kcal/mol. On the other hand, the disordered xanthan and LBG formed gels through backbone-to-backbone interactions, with an E_Int of -262.290 kcal/mol. Overall, the study provides insights into xanthan-galactomannan gel formation and a theoretical basis for the broader application of xanthan.

Impact of octenyl succinic anhydride (OSA) modified starch on the particle size distribution and rheological properties of xanthan gum in aqueous solutions

Effects of addition of octenyl succinate anhydride (OSA) starch on the structural, rheological and thermo-rheological properties of aqueous solutions of 0.5 (w/v %) xanthan gum were evaluated. Analysis by dynamic light scattering revealed the absence of complex formation in the mixed solution. However, it was noticed that an increase in the concentration of OSA starch (COSA) leads simultaneously to an increase of the number of micelles and their self-assembly within the network formed by the xanthan macromolecules. This same mechanism was observed during the evaluation of the rheological properties. For systems containing 0.5 (w/v %) of xanthan and for which COSA ≤ 4 (w/v %), a thermoreversible behavior was found similar to that of xanthan in solution. Furthermore, for COSA ≥ 5 (w/v %), the rheological behavior remained indifferent to the increase in temperature but, scored a spectacular rise in storage modulus when the cooling temperature begins near 70 °C.

Solution properties of imidazolium-based amphiphilic polyelectrolyte in pure- and mixed-solvent media

Mixed solvents that are selectively attractive to different parts of an amphiphilic polyelectrolyte lead to exceptional and promoted solution properties.

Dynamics of polyzwitterions in salt-free and salt solutions

Dynamics of polyzwitterions remains largely unclear. We have prepared zwitterionic poly[1-(3-sulphopropyl) betaine-2-vinylpyridinium] (PSB) and investigated its dynamics in aqueous solution as a function of added salt (NaCl) concentration (Cs) by dynamic laser light scattering (DLS) and sedimentation velocity (SV) in analytical ultracentrifugation (AUC). A fast and a slow mode can be observed by DLS in a salt-free and low-salt solution, where the latter exhibits a maximum intensity at Cs ∼ 10(-3) M. SV measurements demonstrate that the fast mode corresponds to the diffusion of individual chains and the slow mode arises from the dynamic inhomogeneity due to interchain electrostatic repulsion. As Cs increases, the sedimentation coefficient exhibits a maximum at Cs ∼ 0.1 M whereas the diffusion coefficient has a minimum at Cs ∼ 10(-3) M and a maximum at Cs ∼ 0.1 M. Namely, PSB shows a complex dynamics in a salt-free and low-salt solution and anti-polyelectrolyte behavior in a high-salt solution. Our studies reveal that the dynamics of polyzwitterions is mediated by the long range interchain electrostatic repulsion and short range intrachain attraction, which are determined by effective charges on the chains.

Dynamics of single polyelectrolyte chains in salt-free dilute solutions investigated by analytical ultracentrifugation

The dynamics of polyelectrolytes in salt-free solution is an unsolved problem. We have investigated the sedimentation and diffusion of xanthan and poly(N-methyl 4-vinyl pyridine iodide) (P4VPI) in salt-free dilute solutions by analytical ultracentrifugation (AUC) using sedimentation velocity (SV) as a function of polyelectrolyte concentration (Cp). Our study reveals two concentration regimes distinguished in either polyanion (xanthan) or polycation (P4VPI) dilute aqueous solution. When Cp is below the Debye concentration (Cd) at which the chain separation (d) is close to the debye length (lD), the interchain electrostatic repulsion is negligible, and the reciprocal apparent sedimentation coefficient (1/s), apparent diffusion coefficient (D) or reciprocal apparent molecular weight (1/Mw) is linearly related to Cp. In the range Cp > Cd with d < lD, the interchain electrostatic repulsion is present, and the dynamics of polyelectrolytes becomes complex. The real sedimentation coefficient (s0), the diffusion coefficient (D0) and the molecular weight (Mw,0) of the single polyelectrolyte chain in salt-free dilute solution can be obtained by extrapolating the concentration to zero. The present study reveals that the complex dynamics of polyelectrolytes in salt-free dilute solutions arises due to the interchain electrostatic repulsion.