T. V. Laptinskaya

Synthesis and properties of fluorinated derivatives of carbosilane dendrimers of high generations

Fluorinated derivatives containing different amounts of fluorocarbon groups in the surface layer of the molecular structure have been synthesized by the chemical modification of a polyallylcarbosilane dendrimer of the sixth generation via hydrosilylation and heterofunctional condensation procedures. The fluorocontaining dendrimers are well soluble in organic solvents and supercritical CO2. Their properties have been studied by DSC, viscometry, dynamic light scattering, and atomic force microscopy.

Inorganic core/organic shell hybrid nanoparticles: Synthesis and characterization

Core/shell molecular particles, promising components of polymer nanocomposites, were synthesized by condensation of tetraethoxysilane (TEOS) in acetic acid at elevated temperature with subsequent blocking of reactive SiOH groups by trimethylsiloxy groups. Particle diameters ranged from 1 to 10 nm depending on the condensation time until the blocking agent was added. The solubilities of the nanocomposites in THF, toluene, hexane, and other organic solvents made it possible to characterize them by the following physicochemical methods: gel permeation chromatography (GPC), viscometry, dynamic light scattering (DLS), and monolayer compression at the water-air interface. As a result, the particles were found to have compact spherical shapes. The physical state of the particles varied from viscous flow to crystallike depending on the sizes and hardness of their silica cores.

Hyperdiffusive dynamics in conjugated polymer blends and fullerene absorbing solutions

We have observed the hyperdiffusive dynamics of light scatterers accompanied by their ballistic motion by a dynamic light scattering (DLS) technique in blends of semiconducting polymer (poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene], MEH-PPV) with a low-molecular-weight organic acceptor 2,4,7-trinitrofluorenone, TNF) and in fullerene C60 solution. The DLS autocorrelation function has been found to follow the Kohlrausch-Williams-Watt function with the exponent β in the range of 0.5–2, depending on the laser power, scattering vector, optical absorption and type of sample. We show that the hyperdiffusive dynamics (β > 1) results from laser-induced convection caused by optical absorption at the DLS probing wavelength. The convection appears in the DLS data as a ballistic motion with velocities in the range of 5–60 μm s−1 depending on the laser power, type of sample and their absorption. The convection is driven by the local temperature difference, ΔT ∼ 0.1–0.2 K, as evaluated from thermal lens effect measurements. We demonstrate that by decreasing the absorbed laser power, laser-induced hyperdiffusion can be avoided in both the polymer and fullerene samples so that the inherent thermal molecular motion can be probed. Specifically, in the polymer solutions, we have found a slow relaxation mode with the characteristic spatial spectrum of the inverse relaxation time Γs α q4. This mode has been assigned to the coupled motion of entangled conjugated polymer chains.

Dynamic light scattering in sols of a poly(N-vinylcaprolactam) and polyacrylamide mixture

The properties of semidilute solutions of a mixture of polyacrylamide and thermoresponsive polyvinylcaprolactam are studied via dynamic light scattering. It is found that the relaxation time (correlation length) distribution contains several modes. The obtained experimental data are interpreted in terms of the theory describing the dynamics of semidilute and concentrated solutions with allowance for viscoelastic interactions. The investigation of mode dispersion (the dependence of relaxation time on the wave vector of scattering) shows that the fastest and slowest modes are of the diffusion type. The fast mode is the mode of collective diffusion; it may be attributed to the fluctuation motion of polymer units inside blobs. The slowest mode corresponds to the diffusion motion of macromolecule clusters. The rate of relaxation of medium modes nonlinearly depends on the squared wave vector, and these modes are apparently viscoelastic.

Dynamic light scattering in semi-interpenetrating polymer networks based on polyacrylamide and poly(N-vinylcaprolactam)

Semi-interpenetrating networks based on polyacrylamide gel and linear thermosensitive poly(N-vinylcaprolactam) are obtained for the first time and studied via the method of dynamic light scattering. Contributions associated with dynamic fluctuations and frozen inhomogeneities to scattering are determined. It is shown that the ensemble-average scattering intensity strongly depends on the quantity and dimensions of frozen inhomogeneities. As temperature increases, scattering due to both dynamic fluctuations and spatial inhomogeneities tends to increase. At the temperature of the conformational transition of poly(N-vinylcaprolactam), the intensity of scattering increases abruptly, whereas the correlation function assumes the shape of a strongly stretched exponent that corresponds to high relaxation times (∼1 s). It is found that the relaxation-time distribution restored with the use of the inverse Laplace transform contains several modes. For all the studied networks, the correlation length of the mode of cooperative motion (the fast mode) is independent of the concentration of poly(N-vinylcaprolactam) and coincides with the correlation length of the mode of collective motion for the polyacrylamide gel.