Laurence B.
Lurio
Associate Professor
Department
of Physics
(815)
753-6492
l
http://www.niu.edu/~lurio/
B.A.
Columbia University (1985)
Ph.D.
Harvard University (1992)
Postdoctoral
Fellow, Rensselaer Polytechnic Institute (1992)
Research
Scientist, Massachusetts Institute of Technology (1995)
Research Interests
Coherent X-ray Scattering
I am part of a collaborative team working at sector 8, (IMM-CAT) of the Advanced Photon Source (APS) whose chief focus is the production and utilization of coherent x-ray beams. The setup at IMM-CAT prepares beams with laser-like coherence properties through extreme collimation. This is only practical when using high brilliance undulator sources. An important application of coherence is x-ray photon correlation spectroscopy (XPCS). In XPCS a sample illuminated with coherent light yields a speckle pattern which depends on the exact position of all the molecules. The speckle pattern fluctuates in time as the molecules move about. A quantitative analysis of this fluctuation can be inverted to obtain information about molecular length-scale diffusion. My synchrotron-based work is complemented by measurements made at a laboratory at Northern Illinois University. The NIU lab is equipped with a standard laboratory x-ray source, and will have a laser-light scattering apparatus to perform optical photon correlation measurements.
Structure and Dynamics in Polymer Films
and Membranes
Currently
I use XPCS to study the dynamical properties of thin polymer films spun-cast
onto silicon substrates. The random
thermal motion in the polymer films leads to the excitation of surface waves on
the polymers. On length scales larger
than a few hundred nanometers these surface waves are described by the standard
equations of fluid mechanics: the same as would describe waves on the surface
of the ocean. In the case of thin films
one only needs to replace the gravitational force by the Van-der-Waals
attraction to the substrate and note that surface tension and viscosity will
play a much more important role. When
such measurements are extended down to the molecular length scale, such as
characterized by the polymer radius of gyration, continuum fluid mechanics will
to break down. I am presently exploring,
in detail, the crossover from the continuum to the molecular motions.
This work
is also being extended to studies of the dynamical fluctuations
in lipid bilayer membrane systems, using similar techniques. Lipid bilayer
membranes are a major constituent in biological and synthetic membranes with applications
in biosensors and biocompatible materials. Lipid bilayers can be deposited
directly on smooth substrates such as silicon by a variety of techniques,
leaving a thin cushion of water between them and the substrate, or they can be
deposited on a cushion of polymer film deposited on the substrate, or tethered
to the substrate by lipopolymer chains. The structure, conformation and
dynamics of these layered systems are being studied to extract the viscosities
and elastic moduli of membranes. The
dynamics of nanoparticles (Si or Au) incorporated in the membranes are also
under study, as well as corresponding measurements on the membranes within
vesicles in solution.
Randomness
in Quantum Fluids
Another focus of my research is on the behavior of superfluid mixtures of He3 and He4 confined within a random media. The random media is created by imbibing the helium mixtures in an aerogel glass, which consists of a very open randomly-connected silica gel. The aerogels occupy less than 2 percent of the available volume. Their effect on the helium is to act as a weak, random perturbation. When placed in such an environment, mixtures of He3-He4 show a significantly altered phase diagram. In particular, a new superfluid phase rich in He3 appears. This alteration is believed to be a fundamental property that arises solely from the presence of randomness. An alternate explanation would be that the new phase results from surface interactions with the Silica. My measurements have used conventional small angle x-ray scattering to directly measure the correlation between the structure of the glass and the corresponding density modulation in the helium. This information is then used to distinguish the role of randomness from surface and confinement effects.
Selected Publications
- M. D. Brown, B. M. Law, L. Marchand, L. B. Lurio, I. Kuzmenko, T. Gog, and W. A. Hamilton, "X-ray and ellipsometric study of strong critical adsorption," Physical Review E , 2007, 75, 061606.
- L. B. Lurio, N. Mulders, M. Paetkau, M. H. W. Chan, and S. G. J. Mochrie, "Small-angle x-ray scattering measurements of the microstructure of liquid helium mixtures adsorbed in aerogel," Physical Review E, 2007, 76, 011506.
- R. A. Narayanan, P. Thiyagarajan, S. Lewis, A. Bansal, L. S. Schadler, and L. B. Lurio, "Dynamics and internal stress at the nanoscale related to unique thermomechanical behavior in polymer nanocomposites," Physical Review Letters , 2006, 97, 075505.
- L. W.
Marschand, M. Brown, L. B. Lurio, B. M. Law, S. Uran, Ivan Kuzmenko,
- L. B. Lurio, Hyunjung Kim, A. Rühm, J. K. Basu, J. Lal, S. K. Sinha and S. G. J. Mochrie, "Surface Tension and Surface Roughness of Supported Polystyrene Films,” Macromolecules, 2003, 36, 5704–5709.
- Hyunjung, Kim, A. Rühm, L. B. Lurio, J. K. Basu, J. Lal, D. Lumma, S. G. J. Mochrie, and S. K. Sinha, "Surface dynamics of polymer films," Physical Review Letters, 2002, 90, 068302.
- D. Lumma, M. A. Borthwick, P. Falus, L. B. Lurio, and S. G. J. Mochrie, "Equilibrium dynamics in the nondiffusive regime of an entangled polymer blend," Physical Review Letters, 2001, 86, 2042.
- A. Malik, A. R. Sandy, L. B. Lurio, G. B. Stephenson, S. G. J. Mochrie, I. McNulty, and M. Sutton, "Coherent X-ray study of fluctuations during domain coarsening," Physical Review Letters, 1998, 81, 5832-5835.
- L. B. Lurio, T. A. Rabedeau, P. S. Pershan, I. F. Silvera, M. Deutsch, S. D. Kosowsky, and B. M. Ocko, "Liquid-Vapor Density Profile Of Helium - An X-Ray Study," Physical Review Letters, 1992, 68, 2628-2631.