Dynamic surface tension and dilational viscoelasticity of adsorption layers of a hydrophobically modified chitosan

The structure (physical gel) formation within the adsorption layers of the alkylated chitosan via intermolecular hydrophobic interaction or by hydrogen bonding in function of the ageing time (up to tf ∼ 5 × 104 s) has been studied with the help of the two-dimensional dilational rheology by applying sinusoidal deformation to the bubble area within the frequency range of w = 0.05-0.4 rad/s. One characteristic relaxation frequency rheological model of Maxwell has been applied to determine two-dimensional “storage” E′ and “loss” E″ elasticity moduli, as well as the intrinsic elasticity module E0 and the characteristic relaxation frequency ω0 (or the intrinsic viscosity η0 = E0ω0/2π) of the adsorption layer in function of the bulk polymer concentration Cp. It has been shown that the parameters E0 and η0 sharply decrease with increasing Cp. This finding is interpreted on the basis of proposed mechanism explaining the effect of the conformational state of the macro-ions inside the adsorption layers on the Gibbs elasticity and the characteristic relaxation time.