Polyelectrolyte Microstructure in Chitosan Aqueous and Alcohol Solutions

Abstract

This work deals with chain ordering in aqueous and water-alcohol solutions of chitosan. The so-called polyelectrolyte peak is investigated by small-angle synchrotron X-ray scattering. The polyelectrolyte microstructure was characterized by the position of the maximum of the polyelectrolyte scattering peak qmax, which scales with the polymer concentration cp as qmax approximately cp alpha. An evolution of the power law exponent alpha is observed as a function of the degree of acetylation (DA) of chitosan, which is responsible for changes of both the charge density (f) and the hydrophobicity of the polymer chains. The results highlighted the two organization regimes of the theory of Dobrynin and Rubinstein, investigated here for the first time for a natural polymer. At low DAs, alpha approximately 1/2, in agreement with a pearl necklace organization where the structure is controlled by the string between pearls. For higher DA, alpha approximately 1/3, and the correlation revealed by the polyelectrolyte peak is controlled by the pearls. This analysis offers a way to study quantitatively the balance between solvophobic-solvophilic interactions that play an important role in the solution properties of natural polymers. In addition, the role of several parameters acting on the interaction balance were evidenced, such as the nature of the counterion, the composition of the solvent (amount of alcohol in the aqueous solution), and the screening of Coulombic forces by salt addition. Finally, the nanostructure transition from a polyelectrolyte solution to a physical gel is discussed. The gel state is reached when the solvophobic interactions are favored, but depending on the gelation route the polyelectrolyte ordering could be preserved or not.

Critical Dissolution Ionic Strength of Aqueous Solution of Chitosan Hydrochloride Salt

“…8), is comparable to the size of the constituent glucosamine monomers comprising the chitosan chain (ca. 5 Å) [12]. This result tells us that the most of the inter-and intra-molecular electrostatic repulsive interactions between a distance further than 3.5 Å are screened out at I = I * and the nonelectrostatic short-range attractive interactions becomes predominant.…”

“…In contrast, however, most widely studied synthetic polyelectrolytes, for example polystyrene sulfonate (PSS), polyacrylic acid (PA) and polyvinyl sulfuric acid (PVS), possess a vinylic backbone and are anionic in nature. Yet, in spite of such differences, aqueous solutions of chitosan show, in common with solutions of such synthetic polyelectrolytes [11], a smallangle X-ray scattering peak, typical of the polyelectrolyte solution [12]. The presence of a polyelectrolyte peak is due to the quasi-periodic arrangement of the polyions in solution.…”

Characterization of the cathodic electrodeposition of semicrystalline chitosan hydrogel

“…Based on a previous study [19] on the nanostructure of physical chitosan hydrogels obtained from the neutralization of chitosan acetate solutions, the generalized Porod's constant and the Porod's exponent depend on the pH. The scattering pattern of electrodeposited gels is displayed in Fig.…”

Chitosan molecular structure as a function of N‐acetylation

“…11,78 This became even more pronounced by the increase of acetyl groups, which decreases the charged monomer fraction of the polymer, affecting the hydrophobic/hydrophilic balance and promoting interchain hydrophobic interactions. 41,79 A recent work by Ortona et al have showed that the short aliphatic chains on the chitosan backbone is not able to promote an efficient hydrophobic interaction among chains. 72 Thus, it suggests that the hydrophobic contribution for the aggregation process is cooperative, which would involve the sum of the individual hydrophobic sites.…”