Typical Physicochemical Behaviors of Chitosan in Aqueous Solution (original) (raw)
Related papers
Biomacromolecules, 2004
Physicochemical properties of four different homogeneous series of chitosans with degrees of acetylation (DA) and weight-average degrees of polymerization (DP w) ranging from 0 to 70% and 650 to 2600, respectively, were characterized in an ammonium acetate buffer (pH 4.5). Then, the intrinsic viscosity ([η] 0), the root-mean-square z-average of the gyration radius (R G,z), and the second virial coefficient (A 2) were studied by viscometry and static light scattering. The conformation of chitosan, according to DA and DP w , was highlighted through the variations of R and ν parameters, deduced from the scale laws [η] 0) K w M w R and R G,z) K′M w ν , respectively, and the total persistence length (L p,tot). In relation with the different behaviors of chitosan in solution, the conformation varied according to two distinct domains versus DA with a transition range in between. Then, (i) for DA < 25%, chitosan exhibited a flexible conformation; (ii) a transition domain for 25 < DA < 50%, where the chitosan conformation became slightly stiffer and, (iii) for DA > 50%, on increasing DP w and DA, the participation of the excluded volume effect became preponderant and counterbalanced the depletion of the chains by steric effects and long-distance interactions. It was also highlighted that below and beyond a critical DP w,c (ranging from 1 300 to 1 800 for DAs from 70 to 0%, respectively) the flexibility of chitosan chains markedly increased then decreased (for DA > 50%) or became more or less constant (DA < 50%). All the conformations of chitosan with regards to DA and DP w were described in terms of short-distance interactions and excluded volume effect.
Chitosan hydrophobic domains are favoured at low degree of acetylation and molecular weight
Polymer, 2013
The aggregation of chitosan (CS) has been studied as a function of concentration, degree of acetylation (DA), and degree of polymerization (DP) by means of pyrene fluorescence and rheology. Fluorescence experiments show that aggregation of CS involves hydrophobic domains (HD) which are more favoured as lower the DA and DP. Consistent with these results, the viscosity of CS solutions decreases continuously on increasing DA, in the whole range of DP. These results, which rule out the participation of the acetyl groups in the HD, have been interpreted by the theory of hydrophobic polyelectrolytes in terms of the electrostatic energy of the aggregates.
Light Scattering Studies of the Solution Properties of Chitosans of Varying Degrees of Acetylation
Biomacromolecules, 2003
The use of two techniques, differential interferometry and quasi-elastic light scattering (QELS), allowed us to study solutions of chitosan varying in degree of acetylation (DA), degree of dissociation (R), and concentration (C p). With the first technique, we demonstrated the modification of the electric polarizability of the polymer chains, through a law of behavior of the variation of the refractive index increment dn/dC with DA and R. This brought us information on the various kinds of interactions (H-bonds, electrostatic, and hydrophobic) involved in the evolution of the solution properties. QELS experiments performed in dilute regime showed the presence of supramolecular structures depending on DA and R. The topology and the nature of these objects are discussed. The typical presence of aggregates and their evolution with concentration was also demonstrated in semidilute regime.
Langmuir, 2003
The neutralization of a homogeneous series of chitosans with degrees of acetylation (DA) varying between 1% and 71% was followed stepwise by static light scattering. The determination of the gyration radii (RG,z) and the second virial coefficients (A2) allowed us a better understanding of the chitosan behavior during the neutralization in aqueous solutions. On increasing pH, a critical value was evidenced both by a drop of RG,z and a fall of A2. The values of the critical pH were also shown as highly dependent on the polymer concentration and the ionic strength of the media. On increasing DA, the range of pH where chitosan was apparently soluble enlarged although the second virial coefficient decreased with both the increase of DA and the degree of neutralization. Working at the critical pH, just before precipitation occurred, transmission electronic microscopy allowed us to evidence a sol/gel transition responsible for the formation of a stable colloidal dispersion. The average particle sizes increased with the degree of acetylation: from 100 nm for DA) 1% to 300 nm for DA) 51%. These aggregates were probably assembled both by hydrophobic interactions and hydrogen bonding due to the neutralization of the ammonium groups into-NH2.
Two Types of Hydrophobic Aggregates in Aqueous Solutions of Chitosan and Its Hydrophobic Derivative
Biomacromolecules, 2001
The aggregation phenomena in aqueous solutions of hydrophobically modified (HM) chitosan, containing 4 mol % of n-dodecyl side chains, were studied by viscometry and fluorescence spectroscopy with pyrene as a probe. The results are compared with those for unmodified chitosan. Surprisingly, fluorescence data reveal the appearance of intermolecular hydrophobic aggregates both in chitosan and in HM chitosan. Nevertheless, these polymers exhibit quite different rheological properties: upon the formation of aggregates the viscosity of HM chitosan sharply increases, while that of unmodified chitosan raises only slightly. The aggregation models for both chitosan and its hydrophobic derivative were proposed. It was shown that in solutions of HM chitosan two types of hydrophobic domains exist: hydrophobic domains typical for different associating polymers with hydrophobic side chains and hydrophobic domains inherent to chitosan itself.
Journal of Solution Chemistry, 2010
Depolymerization for different time intervals of high molecular weight chitosan using 2 mol⋅L−3 HCl resulted in low molecular weight (LMW) chitosan of 6, 10, 13, 18, and 30 kDa. These were studied using the FT-IR which indicated that the depolymerization process did not influence the chemical structure. LMW chitosan increases the surface tension of water but adjusting the ionic strength (1% NaCl) caused LMW chitosan to reduce the water surface tension. The zeta potential increased with increasing concentration up to a maximum in 1% NaCl solutions. Particle size showed a reduction in size with increasing concentration. This behavior in reduction of particle size was similar to that for the stiffness parameters. These physico-chemical properties showed that LMW chitosan was present in low concentration in its extended form while in higher concentrations it adopted a more contracted form. This change in conformation was confirmed by using molecular modeling where LMW chitosan is ribbon-like to rod-like in solution but becomes rod-like to spherical at the gas–liquid interface.
Macromolecular conformation of chitosan in dilute solution: A new global hydrodynamic approach
Carbohydrate Polymers, 2009
Chitosans of different molar masses were prepared by storing freshly prepared samples for up to 6 months at either 4, 25 or 40°C. The weight-average molar masses, M w and intrinsic viscosities, [g] were then measured using size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS) and a ''rolling ball" viscometer, respectively.
e-Polymers, 2008
Two salts of the biopolymer chitosan were prepared in aqueous medium by employing an excess of HCl or HNO 3 in order to ensure neutralization of all NH 2 -chitosan groups. Chitosan salts were extensively dialyzed in dionised water and dried at 40 ºC until film formation. The films were characterized by thermogravimetry, FTIR and conductimetric tritration. QH + Cl − and QH + NO 3 − salts were viscosimetrically evaluated in free acid aqueous solutions in the presence of NaCl to control ionic strength of the medium. Unexpected high intrinsic viscosity values were obtained at low ionic strength when QH + NO 3 − salt were evaluated.
Hydrophobic derivatives of chitosan: Characterization and rheological behaviour
International Journal of Biological Macromolecules, 1996
Chitosans which are substituted with alkyl chains having a minimum of six carbon atoms demonstrate hydrophobic interactions in solution. The chemical structure of synthetized polymers is determined from NMR spectroscopy and microanalysis and the distribution between the different types of substituted units is obtained. In relation to the rheological behaviour different parameters are studied such as the nature of the hydrophobic chain and the substitution degree, the polymer concentration, the temperature and the ionic content of the polymeric solution. All the observations tend to prove the hydrophobic nature of the interaction mechanism.