physics

physicsfaculty

CWRU Physics Faculty

Charles Rosenblatt
Professor of Physics and Macromolecular Science
S.B., Massachusetts Institute of Technology (1974)
Ph.D., Harvard University (1978)
Condensed Matter Experiment; Liquid Crystals and Complex Fluids
Picture of Charles Rosenblatt
>> Interests << Publications 

Most people are first drawn to liquid crystals by their beautiful optical textures: stars, curves, splotches, and zig-zags, all in a palette of colors rivaling the most ostentatious paintings of modern art. On closer and more scientific inspection one finds that liquid crystals are generally composed of rod-shaped molecules, which exhibit an intermediate degree of order between solid and liquid. For example, in the nematic phase the elongated molecules are orientationally ordered along a particular axis, with no long range positional order. Since the molecules are also optically anisotropic, the polarization state of light may be altered as it passes through the liquid crystal, facilitating the brilliant display of colors. At lower temperatures partial positional order may set in, such that the molecules behave like a liquid in two dimensions, and are nearly solid-like in the third direction. This smectic phase has more than a dozen variations, each with its own characteristic symmetry.

One of my central interests has been the experimental study of phase transitions from one liquid crystalline state to another. The goal of this work is to elucidate the fundamental character of these transitions, and their relationships to other phase changes in nature. I also have spent many years studying the behavior of liquid crystals at a solid interface. How does the interface align the molecules and how does it affect the phase transitions? Can we see analogies between the interface and the behavior in other systems, such as superconductors?

Liquid crystals exhibit fascinating properties on very short length scales, the so-called nanoscopic scale. Using the stylus of an atomic force microscope, we scribe patterns onto a polymer-coated substrate as small as 10 nanometers in length, approximately one-ten thousandth the width of a human hair. The liquid crystal molecules are forced to align parallel to the scribing direction, allowing us to study phase transitions and elastic behavior on very tiny length scales. Along these lines, we recently developed a technique called Optical Nanotomography, where we immerse an ultra-thin optical fiber into a layer of liquid crystal and create a three-dimensional optical image of the liquid crystal’s structure with resolution 1000 times better than other techniques..

A very different sort of scientific program involves controlling the gravitational forces on fluids by. applying an magnetic upward force. For all practical purposes, the fluid becomes weightless, allowing us to study a variety of phenomena. For example, a fluid that is tethered to two solid supports is known as a liquid bridge. Real-life examples include the fluid in the lungs, oil in porous rock, and water that wets a fabric. By studying these fluids in an effective zero-gravity environment, one learns about fluid stability, surface tension, and dynamics. Because the magnet force is controllable with time, we have performed experiments where we have oscillated gravity, and have examined the collapse of a cylindrical liquid bridge when gravity is suddenly turned on. Another research topic involves the Rayleigh- Taylor instability, which occurs when one places a dense fluid on top of a lighter fluid. Under ordinary gravity this arrangement is unstable, but one can stabilize this configuration by use of magnetic levitation of the (magnetic) heavier fluid. On turning off the field, an instability develops, and the heavier fluid falls to the bottom in a very complex manner. This phenomenon occurs in exploding supernovae, inertial confinement in fusion processes for purposes of energy generation, and even in vinegar and oil salad dressing!