Thermodynamics of structured fluids. Hard science for soft materials*
John M. Prausnitz
Chemical Engineering Department, University of California,
Berkeley and Chemical Sciences Division, Lawrence Berkeley National
Laboratory, Berkeley, CA 94720 USA
Abstract: At liquid-like densities, molecules of complex fluids
can assume a variety of structures (or positions) in space; when the
molecules contain many atoms as, for example, in polymers, that variety
becomes very large. Further, when confined to a narrow space, it is
possible to achieve structures that are not normally observed. Thanks
to recent advances in statistical mechanics and molecular physics, and
thanks to increasingly fast computers, it is now possible to calculate
a fluid's structure, that is, the positions of molecules at equilibrium
under given conditions. Calculation of fluid structure is useful because
thermodynamic properties depend strongly on that structure, leading
to possible applications for new materials. Three examples illustrate
some recent developments; each example is presented only schematically
(with a minimum of equations) to indicate the physical basis of the
mathematical description. The first example considers the effect of
branching on self-assembly (micellization) of copolymers (with possible
long-range applications in medicine). The second and third examples
consider the effect of confinement on fluid structure: first, crystallization
in a narrow, confined space to produce a desired crystal structure (with
possible applications for light-emitting diodes) and second, suppression
of micellization of a diblock copolymer in a thin film (with possible
application in lithography). Whenever possible, theoretical calculations
are compared with experimental results.
* Plenary lecture presented at the 16th
IUPAC Conference on Chemical Thermodynamics (ICCT-2000), Halifax, Nova
Scotia, Canada, 6-11 August 2000. Other presentations
are published in this issue, pp. 1799-1849.
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