Prof. Sloutskin's Lab
Head - Soft Condensed Matter Physics Lab
Imaging and Microscopy Research
Prof. Eli Sloutskin, a returning scientist from Harvard University,is a member of the Nano Materials Center at the Institute of Nanotechnology and Advanced Materials (BINA) and is a Senior Lecturer in the Department of Physics.
Crystal Nucleation in Colloidal Spheres
Sloutskin and his team employ confocal microscopy and light scattering to study crystal nucleation in systems of colloids , which are micron-sized particles undergoing Brownian motion in a liquid.
Crystal nucleation is common, yet still poorly understood; theoretical crystallization rates usually miss the experimental values by many orders of magnitude. While colloids form crystals, mimicking atoms and molecules, they are sufficiently large such that the formation of crystalline nuclei is directly observable via sub-particle resolution confocal microscopy.
Sloutskin’s group, in collaboration with the research team of Prof. David Weitz at Harvard, perform three dimensional, real-time tracking of ~5e4 individual particles in a macroscopic colloidal suspension. They detect the formation of the crystalline nuclei, and measure their morphology and size distribution.
The information obtained, which is not available via any other experimental technique, provides a basis for testing the fundamental assumptions of the theories of crystal nucleation.
In contrast with the assumptions of classical nucleation theory, crystalline nuclei are non-spherical. Moreover, instead of being compact, the nuclei adopt a wide range of more ramified shapes. The large variety of shapes accessible to these nuclei entropically stabilizes them, increasing the rate of nucleation by many orders of magnitude.
Spherically Anisotropic Colloids
Most molecules in nature are spherically anisotropic, which gives rise to unique types of collective behavior both in bulk material and within various interfacial phases.
In bulk phases, the anisotropy may give rise to liquid crystalline phases; at the interfaces, the anisotropy may be responsible for the formation of quasi-two-dimensional surface-frozen phases. While the formation of liquid-crystalline phases and surface freezing transitions have been intensively studied during the last decades, conventional techniques do not allow imaging of individual particles in real-time.
Thus, the physical mechanisms driving these phase transitions have remained obscure.Sloutskin’s group employs colloidal spheroids (ellipsoids of revolution) to mimic the behavior of spherically anisotropic atoms and molecules, hoping to shed light on the physics of liquid crystalline phase formation, as well as surface freezing phenomena.
Structure of Non-Crystalline Sediments
One of the most fundamental, yet poorly understood topics in condensed matter physics is the formation of glass and random close-packed materials, which possess the mechanical properties of solids in the absence of long-range crystalline symmetry.
During centrifugation, colloidal particles, density mismatched with their solvent, form a randomly close-packed sediment.
Sloutskin’s team studies colloidal sediments using a combination of analytical centrifugation techniques and confocal microscopy, searching for the fingerprints of a hidden order parameter, which may play an important role in these seemingly random phases of matter.