Critical Dissolution Ionic Strength of Aqueous Solution of Chitosan Hydrochloride Salt

Abstract

The formation of aggregates of chitosan hydrochloride in aqueous solution, with and without added salt (i.e. NaCl), and the dissolution thereof have been studied using wide-dynamical range light transmittance measurements. The concentrations of chitosan and NaCl examined were 4 to 20 g/L and 0 to 2 mol/L, respectively. A large hysteresis loop was found for the formation of aggregates during cooling and the dissolution thereof during heating. In spite of the existence of the hysteresis, and regardless of the precise aggregation state and heating rate, the temperature at which the aggregates dissolved (namely the dissolution temperature) was uniquely determined for any given concentration of chitosan and NaCl. Further a critical dissolution ionic strength, below which no aggregation was detected, was established from the variation of dissolution temperature with ionic strength. The value of the Debye screening length, calculated at the critical dissolution ionic strength, corresponds fairly well to the size of the monomeric units comprising the chitosan chain. We therefore conclude that the aggregates of the chitosan are formed when electrostatic repulsive interactions between chitosan polyions are screened out allowing non-electrostatic attractive interactions to dominate.

Effect of the ultrastructure of chitosan nanoparticles in colloidal stability, quorum quenching and antibacterial activities

“…In water and under an identical range of composition, NP sizes and PdI values were much larger (dashed lines in panels A and C of Figure1). These findings are in general accordance with previous studies[13,54,56], reporting that the addition of adequate amounts of monovalent ions to NP solutions aids in the optimization of the NP hydrodynamic radius and screens the electrostatic repulsion of the charged amino groups present at the pH of the batch CS solution (pH 5.0), leading to increased flexibility, larger degree of compaction of the CS backbone, superior colloidal stability, and lower polydispersity[13,54,56].…”

“…The type of high-purity grade hydrochloride salt form of CS (see Experimental Section) has been manufactured to allow its easy dissolution in water [54]. It is known that the ionic strength of the solvent affects the intrinsic viscosity and chain conformation of CS in polyelectrolyte solutions [55].…”

“…Other laboratories have resolved this issue by resorting to aggressive methods of aggregate disruption, such as ultrasonication [89,90]. Aggregation could be due to the reported tendency of unmodified chitosan particles to produce vortex-resistant aggregates as a result of strong inter-and intra-molecular hydrogen bonding [54,91]. Tanaka et al [54] also mentioned the existence of strong hydrophobic interactions responsible for the aggregation of CS.…”

Solubility of Chitin: Solvents, Solution Behaviors and Their Related Mechanisms

“…critical ionic strength, I c ). Above I c , the dissolution temperature is proportional to the ionic strength, therefore the dissolution temperature increases as the ionic strength of the chitosan solution increases [12].…”

Engineering rheological response in chitosan–sophorolipid systems through controlled interactions

“…The overall inversion of intermolecular forces takes place from negative to positive. This induces gelation of the polyelectrolyte chains [22,23].…”