Adsorption dynamics of hydrophobically modified polymers at an air-water interface

The adsorption dynamics of a series of hydrophobically modified polymers, PAAαCn, at the air-water interface is studied by measuring the dynamic surface tension. The PAAαCn are composed of a poly(acrylic acid) backbone grafted with a percentage α of C8 or C12 alkyl moieties, at pH conditions where the PAA backbone is not charged. The observed adsorption dynamics is very slow and follows a logarithmic behavior at long times indicating the building of an energy barrier which grows over time. After comparison of our experimental results to models from the literature, a new model which accounts for both the deformation of the incoming polymer coils as well as the deformation of the adsorbed pseudo-brush is described. This model enables to fit very well the experimental data. The two fitting parameters give expected values for the monomer size and for the area per adsorbed polymer chain.This article is uploaded in "arXiv.org" https://arxiv.org/abs/1706.0710

Polydopamine layer formation at the liquid – gas interface

The surface properties of a polydopamine layer at the air-water interface were studied by dilatational surface rheology, ellipsometry and Brewster angle microscopy (BAM). A significant increase of the dynamic surface elasticity was discovered when the concentration changed from 0.75 g/l to 2 g/l with the maximum value of about 60 mN/m at a concentration of 1 g/l. The obtained results indicate that the surface film consists of separate domains and the high surface elasticity is a consequence of the interactions between relatively rigid domains of the polymer film. This conclusion was confirmed by Brewster angle microscopy, which demonstrated different steps of the polydopamine film growth. Separate domains appeared at the first step while one can observe a continuous film close to equilibrium. An increase of the initial concentration led to faster polymerization and to the formation of a thicker film. The dynamic surface elasticity decreased in the concentration range from 2 g/l to 5 g/l when the thickness of the polymer film reached about 80 nm. In this case the film could be destroyed in the course of deformation. The cracks in the film resulted in a decrease of the dynamic surface elasticity

Physicochemical study of water-soluble C<inf>60</inf>(OH)<inf>24</inf> fullerenol

© 2020 Elsevier B.V. The article presents novel physicochemical data on C60(OH)24 aqueous solutions. Temperature and concentration dependencies of density (ρ) and speed of sound (u) and surface tension (γ) were obtained. Additionally, the study of human serum albumin (HSA) binding to C60(OH)24 fullerenol was conducted, and thermodynamic characteristics of C60(OH)24–HSA binding were calculated. The obtained values of a binding constant demonstrate that the complexes of C60(OH)24 with HSA are stable and HSA can perform transport functions in the bloodstream. Finally, excess thermodynamic functions of C60(OH)24–H2O binary system were calculated under the application of Virial Decomposition Asymmetric Model (VD-AS) and the boundaries of diffusion stability loss were determined. Aqueous solutions of C60(OH)20 are thermodynamically stable up to xdiff = 6.0 · 10−5. Further concentration increase leads to formation of third-order clusters with linear dimensions of thousands of nanometres and phase separation of the aqueous solution