D. N. Orlova

Polymer hydration and microphase decomposition in poly(N‐vinylcaprolactam)–water complex

Poly(N-vinylcaprolactam) (PVCL) is a synthetic analogue of biomolecules (enzymes, proteins). It demonstrates a specific hydration and undergoes a coil-globule transition. The PVCL-D 2 O system (PVCL mass M = 10 6 ) has been investigated by small-angle neutron scattering (SANS) at T = 296-316 K to identify the structural features of the collapse at concentration C = 0.5 wt% near the threshold of the coil overlap. (The collapse leads to the segregation of the phase enriched with polymer at T > 305 K). The SANS experiments at q = 0.1-5 nm -1 (scales from monomer unit to globule gyration radius R G ≃ 16 nm) have revealed a stretched coil-globule transformation in the range 305-309 K. Using high-resolution SANS (q = 0.002-0.02 nm -1 ) the globule association to form fractal structures (sponge-like) of surface dimension D F ≃ 2.4-2.6 was examined. The coexistence of globules and disordered chains (regions ∼5-10 nm) was found. The growth of the content of globular phase was induced by the conformational transition in disordered molecular fragments from coiled (dimension D ≃ 1.8) to stretched chains (D ≃ 1.2).

Aggregation in Hydroxylated Endohedral Fullerene Solutions

This paper presents some useful results filling the gap in the knowledge about the aggregation of hydroxylated endohedral fullerene Gd@C82(OH)18(contrast agent for magnetic resonance imaging) in aqueous solutions at different pH. A supramolecular ordering study by small-angle neutron scattering has shown that fullerenols exist in cluster form (correlation radius RC ∼ 20–30 nm, fractal dimension D). At pH increasing from 4–5 to 7–8 there was observed a transition from dense branched structures (D ∼ 2.5) to rare coil-like objects (D ∼ 1.5).

Nondestructive characterization of ferrofluids by wide-angle synchrotron light diffraction: crystalline structure and size distribution of colloidal nanoparticles

The combination of magnetic and nonmagnetic interactions between the colloidal particles in ferrofluids results in various local inter-particle correlations that, in turn, change the macroscopic properties of the whole system. Therefore, characterization of the particle ensemble is a crucial point, allowing optimization of a ferrofluid for a particular application. Here it is shown how the crystal structure of the particles can be easily obtained in a fast synchrotron light diffraction experiment without any special treatment of the ferrofluid sample. Moreover, from the same diffraction patterns, such important parameters as particle mean size and dispersion are retrieved; these are compared with the corresponding parameters obtained from electron microscopy data. A particular problem of magnetite–maghemite transformation in nanoparticles stabilized by the surfactant shell is pointed out.

NSE-study of fullerene-containing polymers

Abstract Stars of Poly(styrene) chains grafted to C60 have been studied by SANS and NSE below glass transition (TG∼94∘C). In stars the arms are not condensed at fullerene surface, spreading away from C60-core. The interaction between fullerene core and polymer chains slows down the β-relaxation in arms at T=−20 to +70 ∘ C

Magnetic phase ordering in ferrogels under applied field

Abstract A new cross linked polymer compound (hydrogel) with fine Fe3O4-grains embedded in it has been investigated by neutron scattering. We studied the nanoscale structures of these ferrogels synthesized in a magnetic field and without a magnetic field. By means of polarized neutron scattering we studied the self-assembly of the particles under the influence of the magnetic field. Even in a weak field (H∼65 Oe ) the ferrogel showed strong spatial correlations of the particles; a strong field (H∼4 kOe ) induced slow growth of the interference effect. Over the observation time (several tens of hours) a cluster formation of particles was observed. This magnetic ordering is reversible: it disappears when switching off the external field.

Small‐angle neutron scattering investigation of plastically deformed stainless steel

The microstuctural evolution of plastically deformed steels has been studied by small-angle neutron scattering at ambient temperature in the range of momentum transfer q = (4/)sin(/2) = 0.01-5 nm-1 where is neutron wavelength and is the scattering angle. Samples of austenite stainless steels were pulled on a standard bench to cause a plastic deformation, S = 0-60%, up to the fracture of the material. As a result of the deformation an increase of an order of magnitude was observed in the scatterred intensity I(q)~1/[1+(qRC)2](6-Ds)/2. The analysis of the I(q) distribution has shown the surface fractal nature of the observed nano-scale structures. The evolution of internal surface via intensive growth of pores (size RC~20-40 nm) was found and a linear decrease of the surface fractal dimension 2.9Ds(S)2.1 was observed. These findings can be used to design the fracture criteria for materials of industrial application.

Segmental dynamics in stars of poly(ethylene oxide) chains grafted to fullerene

Abstract We have studied the structure and dynamics of star-shaped poly(ethylene-oxide) (PEO), grafted to fullerene, in D2O-solutions as compared to linear polymer. The neutron scattering gives the radius of stars having a value close to the end-to-end distance of their PEO arms. The spin-echo measurements revealed a strong damping of segmental diffusion in stars showing stretched relaxation behavior.

Small-angle neutron scattering study of high-pressure sintered detonation nanodiamonds

The structure of detonation diamonds sintered at a high pressure (7 GPa) and temperatures of 1200–1700°C has been investigated by small-angle neutron scattering. It is shown that sintering leads to an increase in the particle size from 6 to 30 nm and established that this increase is due to the chainlike oriented attachment of particles. This study supplements the oriented-attachment model, which was suggested based on the X-ray diffraction spectra of detonation nanodiamonds (DNDs) sintered under the same conditions.

NSE-study of poly(N-vinylcaprolactam) by coil–globule transition

Abstract Poly(N-vinylcaprolactam) was studied by SANS and NSE around the coil–globule transition (TC=32°C) at the threshold of overlapping of molecules in D2O-solution ( C=0.5 wt%, mass M=1×106). For T⩾TC chain units’ interaction grown by temperature increase makes coils collapsed. In the dynamics, an anomalous behaviour was observed: together with a slowing down of the diffusion as in the Rouse model, in the globular state the chains demonstrate fast stretched oscillations.

Structure of aluminum alloys irradiated with reactor neutrons

Samples of the CAB-1 alloy in the initial state and irradiated with fast neutrons at an fluence of 2 × 1021 neutrons/cm2 have been studied by small-angle neutron scattering. It has been demonstrated that the observed large scattering cross sections are associated with the presence of nanosized pores with radii R ∼ 5–50 nm in the alloy, whereas for possible inclusions of the Mg2Si and Si phases, the contrast factors and limiting volume fractions lead to the estimated cross sections that are two orders of magnitude smaller than those observed in the experiment. As a result of the irradiation, the volume fraction of scattering objects (pores) 40–50 nm in radius decreases by a factor of more than two. This is compensated, to a large extent, by an increase in the total fraction of particles with radii of 5–8 and 20–25 nm as the total surface area of the scattering objects increases by 40%.