N. V. Tsvetkov

Conformational, optical, electro-optical, and dynamic characteristics of cross-linked poly(N-acryloyl-11-aminoundecanoic acid)

Polymerizable surfactants now attract a great interest due to high potential of their practical application as components of pseudostationary phase in micellar chromatography, drug carriers, and “building blocks” for molecular design of nanoparticles and nanostructured polymer materials, for encapsulation of various biological preparations. In the present work, we have studied poly(N-acryloyl-11-aminoundecanoic acid) (cross-linked comb-like polymer). Cross-linked polymers were obtained via copolymerization of the surfactant bearing double bond in hydrophobic tail with hydrophobic bifunctional cross-linker in micellar solution. Of special interest was the comparison between cross-linked and non-cross-linked polymers and influence of alkaline medium on characteristics of these samples. Non-cross-linked polymers were obtained by hydrolysis of the cross-linked product (treating with NaOH). The mixture of cyclohexanol and dioxane (1:1 volume ratio) was used as a solvent. Detailed studies of the obtained polymers by viscometry, dynamic light scattering, flow birefringence, and equilibrium and non-equilibrium electric birefringence were performed. It was established that during cross-linking process, two types of bonds are formed (the ones inside individual molecules and between several polymer chains). It was shown that cross-linked macromolecular nanoparticles can be transformed into comb-like polymers.

Conformational and optical properties of macromolecules of some aliphatic-substituted cellulose esters

Synthesized cellulose pelargonates, tridecanoates, valerates, and acetovalerates of various molecular weights are studied in chloroform, dioxane, and tetrachloroethane solutions by the methods of isothermal translational diffusion, sedimentation velocity method, flow birefringence (dynamooptical Maxwell effect), viscometry, and equilibrium electric birefringence (Kerr effect). The equilibrium polymer rigidities are determined and the role of the solvent and temperature in the formation of the conformational characteristics of the macromolecules under study is analyzed. The values of the intrinsic optical anisotropy of the monomeric units of the studied cellulose esters are experimentally determined. The contribution of the side chains to the optical anisotropy of the macromolecules of cellulose esters with aliphatic substituents is analyzed. The results obtained in this study are compared with the data on the cellulose esters with the aliphatic side substituents studied earlier. For the studied samples, the values of the longitudinal components of the monomeric unit dipoles in a nonpolar solvent are estimated.

Formation of interpolyelectrolyte complexes with controlled hydrodynamic radii in solutions

Interpolyelectrolyte complexes (IPEC) of poly(2-acrylamido-2-methylpropanesulfonic acid) (PAMPS) and comb-like amphiphilic polyelectrolyte poly(11-acryloyloxyundecyltrimethyl-ammonium) cation (PAUTA) were synthesized via polymerization of AUTA ionically bound to a PAMPS macromolecule. Nanoparticle dispersions with controlled hydrodynamic radii were prepared by varying molecular weight of the initial PAMPS. The morphology and sizes of IPEC dispersions were studied by atomic force microscopy (AFM). Nanoparticles dispersions stability under different salt conditions was assessed.

Disk-like nanocrystals prepared by solvolysis from regenerated cellulose and colloid properties of their hydrosols

One possible way of obtaining cellulose nanocrystals and aqueous sols with novel properties is based on modification of supramolecular structure of the polysaccharide. This modification involves rearrangements of hydrogen bonds and has an effect on polymer morphology, formation of surface reactive sites and interface interactions. Disc-like nanocrystals of cellulose II were prepared by solvolysis of regenerated cellulose in acetic acid/octanol medium in the presence of 0.4 mol% of phosphotungstic acid. The starting cellulose samples were dissolved and regenerated in the NaOH/thiourea system. Cellulose nanocrystals were studied by transmission electron microscopy, atomic force microscopy, dynamic light scattering, FTIR spectroscopy, XRD and thermogravimetric analysis. Colloidal stability of aqueous suspensions of cellulose nanocrystals in the presence of electrolyte (KCl) was studied. Their acid-base properties were revealed using potentiometric titration. The influence of electrolyte concentration on dynamic viscosity of the obtained hydrosols and their ability to show birefringence was established.

Regulation of structure, rheological and surface properties of chitin nanocrystal dispersions

The hydrosols of chitin nanocrystals (ChN) are promising as modifiers of properties, drug delivery systems, and media. The purpose of this work is to clarify the mechanisms for regulating processes of stability and structure formation occurring in the ChN hydrosols under the influence of varying ionic strength. ChN were isolated from the crab shell; ChN hydrosols are obtained with different concentrations of the dispersed phase. The structure and morphology of the particles was studied by atomic force microscopy and X-ray diffraction. Hydrosols were studied by rotational viscometry, dynamic light scattering, and photometry in the presence of KCl with concentration up to 200mM. The experimental results of finding the rapid coagulation threshold are compared with calculated ones performed with the use of the modified DLVO theory. It is established that in the range of electrolyte concentrations 30∼75mM, the optical and rheological properties of the ChN hydrosols undergo crucial changes. At an electrolyte concentration of 20∼150mM, particles coagulate at a secondary potential minimum; the parallel orientation of the particles is energetically more advantageous. In systems with a higher concentration of electrolyte, there is no potential barrier; rapid barrier-free coagulation is observed, with the formation of stronger coagulation contacts and the formation of stable gels.