Characterization of Clusters and Unimers in Associating Solutions of Chitosan by Dynamic and Static Light Scattering

Abstract

Association of two chitosans of different degrees of acetylation (DA) is studied in dilute water/acid/salt solutions by combined analysis of static and dynamic light scattering. The influence of sodium salt anions Cl − and CH 3 COO − on conformation of macromolecules and properties of clusters was studied. At DA = 15 mol%, the macromolecules exist either in rigid-rod (R g /R h = 2.7) or in coil (R g /R h = 1.8) conformations in the solvents containing NaCl and CH 3 COONa, respectively. Chitosans with higher DA = 28% dissolved in the solvent containing CH 3 COONa are in the collapsed state (R g /R h < 0.8), predicted by Dobrynin (Macromolecules, 2004). The clusters are of spherical form (0.8 < R g /R h < 1.2). CH 3 COONa promotes higher fractal dimensionality of clusters (2.2-2.4) than NaCl (1.9). Higher critical aggregation concentration is observed in NaCl. The other hydrodynamic methods (capillary viscometry, velocity sedimentation, and Tsvetkov diffusometry) do not detect the clusters, probably, because of their disruption during flow.

Interfacial Properties of Chitosan in Interfacial Shear and Capsule Compression

“…Smaller changes in interfacial tensions have been reported for increasingly polar oil/water interfaces stabilized by the protein β-lactoglobulin, which may be considered a soft particle at the interface . The lack of chitosan surface activity in the absence of buffer is consistent with previous oil/water interface studies. , The decrease of interfacial tension of chitosan in the buffer solution in comparison to the buffer-only solution suggests that the chitosan is surface active. What is more difficult to determine from these data alone is if the chitosan is competing with the buffer for the interface.…”

“…The oil/water interface imaging shows an adsorbed layer of aggregated particles 50–100 nm in diameter interspersed around large nonspherical aggregates. The larger nonspherical aggregates appear to be a feature of the layer, as no large particles were observed in light-scattering experiments, which showed a monodisperse 20–30 nm diameter particle (see Figure C) and a small population of doublets also observed by Skorik et al , All particles observed are stationary and do not move while imaging as observed by others, indicating that they are well adhered or incorporated into the layer. The observation of particles at both the aqueous and nonaqueous sides of the adsorption layer while forming a thick film indicates that densely packed particulates form multiple layers at the interface.…”

“…Furthermore, without the addition of the salt, there does not appear to be any particles formed below pH 5. Previous studies with lower salt concentrations and unreported pH conditions in sodium chloride and sodium acetate have shown similar sized particles, where the chain length and deacetylation degree strongly affect the particle size of the chitosan. In the experiments in the present work, increasing the concentration to 1 M of sodium acetate did not impact the formation of the chitosan particles, in contrast to previous studies where the addition of sodium chloride was shown previously to produce smaller chitosan particles than sodium acetate. , …”

“…Previous studies have shown chitosan to be an adequate stabilizer of oil/water emulsions. ,, Interfacial tension (IFT) studies have shown that chitosan has a low surface activity at the air/water interface in acetate buffer with little added electrolyte. , Below 0.3 M of sodium chloride or sodium acetate in aqueous solution, , low concentrations of chitosan reduces the interfacial tension slightly, with a strong decrease in IFT requiring high concentrations (>0.5 % wt) of chitosan . Studies observing the surface tension of chitosan above 0.3 M of sodium acetate show a dramatic increase in the interfacial activity of chitosan, where the surface tension decreased significantly (Π ∼ 30 mN/m). , Furthermore, when adsorbed chitosan films formed at the air/water interface were studied using dilational rheology, a significant increase in the dilational moduli was observed with the addition of 0.3 M of sodium acetate.…”

“…14 The addition of these species can lead to self-assembled complexes that exhibit new functionality such as drug holding capacity 9 or interfacial behavior. 15 In addition, Skorik et al 16 recently have shown that chitosan may also form colloidally stable aggregated particles that self-assemble in 0.3 M sodium chloride and sodium acetate solutions, creating stable nanoparticles between 10 and 30 nm in diameter. These nanoparticle solutions exhibit increased hydrophobicity in pyrene fluorescence studies, 17 suggesting that these nanoparticles may have promising interfacial properties.…”