Science | Igor Dolbnya

Igor Dolbnya
Test Beamline

Igor Dolbnya Igor Dolbnya is the Beamline Scientist on the Test Beamline, B16. Prior to joining Diamond, he was a Beamline Scientist at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, where he undertook research into the structure, phase transition phenomena and dynamics of different soft-condensed matter systems: colloids, polymers, colloidal and liquid crystals using X-ray scattering/diffraction and X-ray photon correlation spectroscopy techniques.

Email: Igor Dolbnya
Tel: +44 (0) 1235 778516
Beamline B16: Test Beamline

Key research areas

X-ray diffraction and scattering, Colloids, Liquid crystals, Order/Disorder

Current Resarch Interests

Colloidal suspensions that form periodic self-assembling structures on sub-micrometer scales are of interest from the perspectives of both fundamental science and potential technology. Suspensions of hard-sphere colloids display an entropy driven fluid-crystal transition. This remarkable phenomenon widely serves as a simple model of crystallization in atomic and molecular systems. By tuning the interparticle interaction potential, various lattices such as face centred cubic (fcc), random-stacking hexagonal close-packed (rhcp), body-centred cubic (bcc) and body-centred tetragonal (bct) can be made.

Self-assembly of colloidal particles into crystalline structures also attracts significant attention as a technique for inexpensive, large-scale fabrication of photonic band gap materials. For these applications the emphasis is on the preparation of large single crystals possessing long-range order, with a low density of defects and small fluctuations of the particle positions. The growth of millimeter-large colloidal crystals has been reported by many researchers, while the actual order parameters were hardly ever addressed. The development of the high-resolution small-angle X-ray diffraction technique on synchrotrons allowed me to perform the detailed characterization of long-range order parameters, particularly in hard sphere crystals.

Another focus of my research was studying the dynamics of freely-suspended liquid crystal (LC) films. Long-range translational order is a defining quality of 3D crystals; it leads to the existence of Bragg reflections in X-ray scattering patterns. In contrast, monomer and polymer smectic LC phases consist of stacks of liquid layers in which strong thermal fluctuations cause the mean-squared layer displacements of the layer positions to diverge logarithmically with the system size (Landau-Peierls instability). These smectic membranes have a controlled thickness (from two to thousands of layers) while the layers order uniformly parallel to the surfaces. To study their dynamics, X-ray photon correlation spectroscopy (XPCS) using the coherent x-rays at ESRF (Grenoble) has been combined with neutron spin echo (NSE) measurements at ILL (Grenoble). This allowed us to measure a new area, that of relaxation times in the range from 10 ns up to 10-100 s. Fluctuations of a specific wavelength could be probed at different off-specular scattering positions.

Selected Publications

  1. Microradian X-ray diffraction in colloidal photonic crystals, Petukhov A.V., Thijssen J.H.J., ’t Hart D.C., Imhof A., van Blaaderen A., Dolbnya I.P., Snigirev A., Moussaıd A. and Snigireva I., Journal of Applied Crystallography 39 (2), 137-144 (2006).
  2. Coexistence of rhcp and fcc phases in hard-sphere colloidal crystals, Dolbnya I.P., Petukhov A.V., Aarts D.G.A.L., Vroege G.J. and Lekkerkerker H.N.W., Europhysics Letters 72 (6), 962-968 (2005).
  3. Observation of a hexatic columnar liquid crystal of polydisperse colloidal disks, Petukhov A.V., van der Beek D., Dullens R.P.A., Dolbnya I.P., Vroege G.J., Lekkerkerker H.N.W., Phys. Rev. Letters 95 (7), 077801 (2005).
  4. X-ray photon correlation spectroscopy in a reflection geometry: Coherence and resolution, Sikharulidze I., Dolbnya I.P., Madsen A., de Jeu W.H., Optics Communications 247 (1-3), 111-124 (2005).
  5. Bragg Rods and Multiple X-Ray Scattering in Random-Stacking Colloidal Crystals, Petukhov A.V., Dolbnya I.P., Aarts D.G.A.L., Vroege G.J. and Lekkerkerker H.N.W., Phys. Rev. Letters 90, 028304 (2003).
  6. Surface and bulk elasticity determined fluctuation regimes in smectic membranes, Sikharulidze I., Farago B., Dolbnya I.P., Madsen A., de Jeu W.H., Phys. Rev. Letters 91, 165504 (2003).