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A V Petukhov

Publications and source records attributed to A V Petukhov.

9 recordsLinked to original sources
PubMed2006

Magnetic-field-induced orientational order in the isotropic phase of hard colloidal platelets.

The magnetic-field-induced orientational order in the isotropic phase of colloidal gibbsite [Al(OH)3] platelets is studied by means of optical birefringence and small-angle x-ray scattering (SAXS) techniques. The suspensions display field-induced ordering at moderate field strengths (a few Tesla), which increases with increasing particle concentration. The gibbsite particles align their normals perpendicular to the magnetic field and hence possess a negative anisotropy of their diamagnetic susceptibility Delta(chi). The results can be described following a simple, Onsager-like approach. A simplified model is derived that allows one to obtain the orientational distribution function directly from the scattering data. However, it leads to an underestimate of the diamagnetic susceptibility anisotropy Delta(chi). This accounts for the difference between the Delta(chi) values provided by the two experimental techniques (SAXS and magneto-optics). The order of magnitude Delta(chi) approximately 10(-22) J/T(2) lies in between that of goethite suspensions and that of suspensions of organic particles.

Journal Article↗
PubMed2005

Observation of a hexatic columnar liquid crystal of polydisperse colloidal disks.

We report the observation of a new type of columnar liquid crystal phase, which is formed by thin hard colloidal disks in a dense suspension. High-resolution small-angle x-ray diffraction reveals a combination of long-range bond-orientational order and short-range translational order between the columns, the hallmark of the hexatic phase. Our results imply that geometric frustration related to the size polydispersity of the particles destroys long-range translational order and therefore promotes the formation of this novel phase.

Journal Article↗
PubMed2005

Evidence of the hexagonal columnar liquid-crystal phase of hard colloidal platelets by high-resolution SAXS.

We report Small-Angle X-ray Scattering (SAXS) measurements of the columnar phase of hard colloidal gibbsite platelets. We have been able to create large oriented domains of the columnar phase both perpendicular and parallel to the sample wall, varying the volume fraction of platelets and adding non-adsorbing polymer to the dispersion. In conjunction with the increased resolution of the SAXS setup, this allowed a detailed analysis of the columnar phase, providing unambiguous evidence for the hexagonal nature of the phase.

Colloids↗
PubMed2004

Destruction of long-range order recorded with in situ small-angle x-ray diffraction in drying colloidal crystals.

High-resolution synchrotron small-angle x-ray diffraction is applied to characterize the structure and long-range order in a sedimentary hard-sphere colloidal crystal before and during its drying. The principles of the technique and the influence of the coherence properties of the x-ray beam are discussed in detail. The capillary forces generated during the drying process are shown to destroy the long-range order and to break the crystal into smaller crystallites with slightly different orientations. The diffraction is shown to switch from the dynamic regime in the long-range-ordered crystal to nearly kinematic diffraction in the mosaic (short-range-ordered) crystal.

Journal Article↗
PubMed2003

Bragg rods and multiple X-ray scattering in random-stacking colloidal crystals.

Synchrotron small-angle x-ray diffraction images of random-stacking-induced Bragg scattering rods are obtained in a wide range of wave vectors from a single colloidal crystal. The results reveal a strong multiple scattering effect, which leads to new features in the diffraction pattern-secondary Bragg rods. We argue that dynamic x-ray diffraction is rather common for high-quality colloidal photonic crystals and should be taken into account.

Journal Article↗
PubMed2002

High-resolution small-angle x-ray diffraction study of long-range order in hard-sphere colloidal crystals.

The long-range order parameters in single crystals of hard colloidal spheres grown in sediments of colloid-polymer mixtures are determined using synchrotron small-angle x-ray diffraction with a resolution of 10(-6) of the wave vector. The interplanar positional order derived from the width of lattice reflections extends over at least 500 lattice planes. The lattice planes are orientationally correlated within approximately 0.1 degrees throughout the crystals, whereas the stacking of hexagonal planes remains random.

Journal Article↗
PubMed2000

Strong surface state effects in nonlinear magneto-optical response of Ni(110).

Spectroscopic magnetization-induced optical second harmonic generation (MSHG) measurements from a clean Ni(110) surface reveal strong resonance effects near 2.7 eV that can be attributed to the presence of an empty surface state. The good agreement with model calculations shows the potential of MSHG to probe spin-polarized interface band structures.

Journal Article↗