We study the physics of complex fluids. These are systems
that are generally intermediate in their degree of ordering,
between liquid and crystal states. Examples are liquid crystals,
colloidal suspensions, molecular aggregates in solutions,
and polymer solutions. These systems are studied by various
methods, and with several goals. One goal is to understand
the macroscopic properties and the fascinating phenomenology
of these systems, and the other major goal is to understand
how these systems order, the role of the forces that are
important, and how their microscopic properties and the
nature of their ordering dictate their macroscopic properties.
In the case of liquid crystals, macroscopic phenomena
involving the response to electric and magnetic fields,
surface orienting forces, and flow fields are especially
interesting. A variety of complex effects are observed,
by optical microscopy and other optical methods, and analyzed
in terms of the elastic and viscous properties of the liquid
crystal. In turn, these phenomena are used to measure the
elastic constants, viscosities, and other basic macroscopic
parameters describing the liquid crystals. Then, starting
from knowledge and ideas about the molecular properties
of the system under study, and how its molecules are ordered,
models are developed to account for the macroscopic parameters
that are measured. For example, liquid crystals based on
solutions of rigid polymers are studied. The microscopic
variables that are important, and can be varied experimentally,
are the length of the polymer chains, their concentration
in solution, and the degree of rigidity of the polymer.
These all affect the macroscopic elastic and viscous coefficients
of the liquid crystals, and change the nature of its response
to applied external forces, such as electric and magnetic
fields.
In the case of colloidal suspensions of Tobacco Mosaic
Virus particles, again the interplay between microscopic
and macroscopic properties is very rich. These rigid rod-like
particles are stabilized in suspension in water by repulsive
electrostatic interactions. The ionic strength of the solution,
and the concentration of virus particles, change the nature
of the ordered phases exhibited by this system. One observes
isotropic liquid-like order, a nematic phase, a smectic
A phase, a columnar hexagonal phase, and a crystalline phase,
in all of which the virus particles constitute only a small
fraction of the volume of the system. The detailed understanding
of this rather simple physical system is important for deepening
our general knowledge about how small particles in solution
interact and spontaneously order.
For solutions of molecular aggregates, there are more
complex questions concerning molecular interactions and
ordering, because order exists at several scales. First,
the molecules order into rod-like aggregates, due to their
basic attractive interactions with one another, and their
complex interaction with the water surrounding them. Then,
the rod-like aggregates interact to form various liquid
crystal ordered phases. Again, ionic strength, concentration
of the solution, and temperature all play roles in determining
the macroscopic properties of the system. In addition to
the macroscopic techniques used to study the systems mentioned
above, x-ray diffraction and computerized molecular modeling
play a crucial role in developing an understanding of these
systems.
Recent Publications:
Lee JB, Konovalov D, Meyer RB. Textural transformations
in islands on free standing smectic-C* liquid crystal films.
(May 2006) Phys Rev E Stat Nonlin Soft Matter Phys.
73(5 Pt 1):051705. [abstract]
Verduzco R, Meng G, Kornfield JA, Meyer RB. (April 2006)
Buckling instability in liquid crystalline physical gels.
Phys Rev Lett. 96(14):147802. Epub 2006 Apr
13. [abstract]
Palffy-Muhoray P, Meyer RB. (March 2004) Bridging the experiment-theory
gap. Nat Mater. 3(3):139-40.
Pelcovits RA, Meyer RB. (Sept 2002) Isotropic-cholesteric
transition in liquid-crystalline gels. Phys Rev E Stat
Nonlin Soft Matter Phys. 66(3 Pt 1):031706. [abstract]
Last reviewed: January 24, 2007. E-mail comments
or questions to the webmaster.
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