Multichain Aggregates in Dilute Solutions of Associating Polyelectrolyte Keeping a Constant Size at the Increase in the Chain Length of Individual Macromolecules

Abstract

Multichain aggregates together with individual macromolecules were detected by light scattering in dilute aqueous solutions of chitosan and of its hydrophobic derivatives bearing 4 mol % of n-dodecyl side groups. It was demonstrated that the size of aggregates and their aggregation numbers increase at the introduction of hydrophobic side groups into polymer chains. The key result concerns the effect of the chain length of individual macromolecules on the aggregation behavior. It was shown that for both unmodified and hydrophobically modified (HM) chitosan, the size of aggregates is independent of the length of single chains, which may result from the electrostatic nature of the stabilization of aggregates. At the same time, the number of macromolecules in one aggregate increases significantly with decreasing length of single chains to provide a sufficient number of associating groups to stabilize the aggregate. The analysis of the light scattering data together with TEM results suggests that the aggregates of chitosan and HM chitosan represent spherical hydrogel particles with denser core and looser shell covered with dangling chains.

Aggregation behaviour of gold nanoparticles in presence of chitosan

“…That concentration, already used in a similar previous work (Pamies et al 2010), is about the critical overlap concentration, c*, for the case of our CS solution (Cho et al 2006;Morariu et al 2012). One can estimate c* from the product c* solutions (both salty and obviously salt-free) are nondilute and the CS chains form aggregates of varying size which characteristics will depend on both the CS intrinsic features and the environmental conditions (Schatz et al 2003;Popa-Nita et al 2010;Korchagina and Philippova 2010). Figure 3 shows size distributions for 0.001 g/cm 3 CS solutions at pH 4 corresponding to both salt-free conditions (I = 0 M) and high ionic strength (I = 0.25 M).…”

Chitosan and its hydrophobic derivatives: Preparation and aggregation in dilute aqueous solutions

“…It is of interest that, in some cases [42,49], the aggregation of chitosan follows the "closed" pattern; that is, the radii of gyration of aggregates remain unchanged with polymer concentration, while in other cases [49], a concentration dependence of the radius of gyration appears: Aggregates grow with the chitosan concentration. This behavior corresponds to the "open" type of association.…”

“…This behavior corresponds to the "open" type of association. Closed association is usually observed [42] at low pH values, when chitosan macromolecules are fully protonated and the salt con centration is insufficient for full shielding of charged groups. In this case, the aggregates cannot grow, oth erwise their charge will exceed a critical value; as a result, the aggregates will be destroyed because of enhanced repulsion.…”

“…The effect of the length of chitosan macromole cules on their aggregation in an aqueous solution was studied by light scattering [42]. It was demonstrated that the radii of aggregates are independent of the chain length of their constituent macromolecules.…”

“…However, self aggregates of chitosan, which show promise as carriers of drugs and genes, are of special interest. Knowledge of the regularities controlling the formation of aggregates and factors determining their dimensions make it pos sible to prepare carriers with desired dimensions [42]. Self aggregates may be stabilized via covalent crosslinking, for example, with glutaraldehyde [57][58][59][60][61], epichlorohydrin [62] or diisocyanate [63].…”