I. V. Postnova

Bionanocomposite from self-assembled building blocks of nacre-like crystalline polymorph of chitosan with clay nanoplatelets

Biopolymers are biocompatible and nontoxic but their other properties rank much below synthetic polymers. Their mechanical performance is improved significantly in bionanocomposites with a layered brick-and-mortar structure biomimicking the nacre of a crustaceous shell after integration with nanoparticles. Biopolymers are found in a disordered state, whereas crustaceans hold chitin in a crystalline form. Herein, it is biomimicked in a bionanocomposite of chitosan with clay nanoplatelets. Films were prepared using a new one-pot technique combining an initial formation in situ of building blocks of clay nanoplatelets and chitosan macromolecules charged progressively in their presence with evaporation-induced self-assembly, which results in highly ordered nanocrystalline narrow rectangle microparticles of thickness is ca. 15 nm that are made from interstratified layers of a new crystalline polymorph of chitosan with nanoplatelets. Its presence and structure is characterized by small/wide-angle X-ray scattering, scanning and transmission electron microscopy, microRaman spectroscopy. Crystalline polymorph can be separated easily. It is insoluble in water and organics that provide scope for its use in nanocomposites.

Alginate polyelectrolyte complexes with cationic hydroxyethyl cellulose derivatives: Role of the block structure

It was shown that the block structure of alginate significantly affects the mechanism of formation and properties of its water-soluble polyelectrolyte complexes with cationic derivatives of hydroxyethyl cellulose. Alginate that contains residues of only mannuronic acid remains in solution in the form of coils, and the incorporation of guluronic acid residues gives rise to formation of a network structure. A difference in the structure of polyelectrolyte complexes is explained by different rigidities of blocks formed by residues of mannuronic and guluronic acids having different conformations of the pyranose ring.

Thermal modification of optical properties of silicate nanocomposites based on cadmium sulfide quantum dots

Abstract. Here, we report the studies of thermal treatment effect on the structural and optical properties of nanocomposites based on cadmium sulfide quantum dots embedded in a silicate matrix. An explanation of the mechanism of reversible photoinduced absorption of the nanocomposite has been given. It is found that heating at 180°C results in significant changing of nanocomposite absorption and luminescence spectra caused by structural changes of quantum dots. It is found that photoinduced optical absorption of the nanocomposite is caused by amorphous-structured cadmium sulfide quantum dots.

Erratum to: One-stage immobilization of the microalga Porphyridium purpureum using a biocompatible silica precursor and study of the fluorescence of its pigments

The biocompatible silica precursor tetrakis(2-hydroxyethyl)orthosilicate with ethylene glycol residues was used instead of the common alcohol-containing tetraethoxysilane for the first time to prepare a biorecognition element by entrapping the marine microalga Porphyridium purpureum into a silica matrix by a one-stage sol–gel procedure at conditions (pH, ionic strength, and temperature) appropriate for living cells. We show that the microalga immobilized in this way fully maintains its viability and functionality. We furthermore show that the silica matrix had a stabilizing effect, providing microalgal survival and functionality at increased temperature. The high optical transparency of the silica matrix allowed us to study the optical properties of Porphyridium purpureum thoroughly. When irradiated by a laser, intense fluorescence of chlorophyll-a and phycoerythrin of the photosynthetic system was observed. The characteristics of this fluorescence differed notably from that observed with P. purpureum in suspension before immobilization; possible reasons for this and an underlying mechanism are discussed.

The influence of titanium dioxide to nonlinear optical properties of carbon quantum dots

Investigation of nonlinear optical properties of solutions of carbon quantum dots synthesized by hydrothermal synthesis of chitin before and after coating with titanium dioxide. It is shown that the titanium dioxide has an activating effect, allows varying the carbon quantum dots non-linear characteristics.

Structural features of nanocomposites based on cadmium sulfide nanoparticles in glass matrix

We study stable stable transparent monolithic nanocomposites based on the silica matrix doped with CdS nanoparticles (NPs) of different nature. The first kind of nanocomposite was obtained by nucleation and growth of nanoparticles in glass matrix during heat treatment. The second nanocomposite was obtained by immobilization of pre-made nanoparticles into silica gel matrix. This work is focused on characterization of the nanocomposites in the submicron scale by using electron microscopy and small angle x-ray scattering techniques. Experimental results show that both types of nanocomposites have homogeneous distribution of quantum dots. Form-factor and average size of CdS NPs depend on the synthesis technique

Nanocomposites Based on CdS Quantum Dots for Laser Control Devices

Here we report about study the novel class of nanocomposite for optical control devices. It was observed that nanocomposite based on cadmium sulfide quantum dots in silica matrix can change its optical properties under irradiation of UV-light. These changes are expressed as increasing of optical absorbance coefficient and not only decreasing of luminescence intensity but in some cases red-shifting of maximum. Dependence of quantum dot optical properties upon the kind of matrix and polarization degree of modifying radiation was obtained.