This is the second of a short series on the federal budget process. Here, we will focus on how the science budget is set inside the Executive Office of the President. The main players here are the Office of Management and Budget (OMB) and the Office of Science and Technology Policy (OSTP).

The budget process for a given fiscal year starts in the agencies. For example, the fiscal year 1991 budget request to Congress was put together by the agencies during the winter, spring and summer of 1989. In the Department of Energy (DOE) for example, budget requests are obtained from the field offices. Typically, these requests are an exercise in optimism, founded on the time-honored notion that you are certain to get nothing if you don't at least ask.

In any event, DOE headquarters staff, after receiving these requests, pare down the totals in a process not unlike that followed within the OMB. This can resuit in weeping and gnashing of teeth at the field offices even at this early stage. While not generally appreciated, OMB staff can often do much of their budget cutting work before even receiving the formal budget request by a judicious combination of friendly advice, jawboning or more extreme measures which this writer will not go into. (On a more positive note, previous administration guidance—e.g., a planned doubling of the National Science Foundation (NSF) budget in five years, or a commitment to a given schedule for space probes, satellites, etc., in the case of NASA—can largely “hard wire” the budget process before the budget submission to OMB).

The goal of this issue of the MRS BULLETIN, with its focus on the physics of complex materials, is to point out some of the fascinating features, both fundamental and applied, of complex materials: liquid crystals and polymers. Over the past 20 years, we have witnessed impressive advances in the understanding of liquid crystals and polymers on all fronts—physics, chemistry, materials research, and applications.

Physicists are interested in the fundamentals of a phenomenon. Our assumption is that once we understand how the pieces of a System work, the understanding of how the whole System works immediately follows. However, those of us who have been involved in materials physics research quickly learn that complexity generates rules of its own on scales much larger than the microscopic scale of the molecules involved. Some-times these rules are beautifully simple and elegantly described, but most often they are not. The following articles high-light some important current research in the domain of complex materials, particularly for liquid crystals and polymers.

Contributing to this special issue are: Pierre-Gilles de Gennes; J. William Doane; Wolfgang Meier and Heino Finkelmann; Paul Keyes; Patrick Oswald, John Bechhoefer and Francisco Melo; and Walter Zimmerman. They give us their current thinking on polymers in shear, novel electro-mechanical effects observed in polymeric liquid crystals, and how liquid crystals in a solid polymer matrix make useful high-speed color displays.

In spite of its importance for extrusion and molding, the rheology of polymer melts under high shear rates is not fully explained by the classical theory of Doi and Edwards. In this theory, each polymer chain is trapped in a confining “tube.” When the tube is suddenly stretched, the chain follows at first, but it soon shrinks back to its original length (“retraction process”). I propose a different view: Upon stretching, the tube becomes thinner so the chain is squeezed and tends to span a longer length of tube; there is no retraction.

The idea of dispersing micron-size birefringent particles in a polymer to selectively scatter light is not new. In the 1930s Land patented a light polarizing material in which small, oriented solid crystallites were suspended in a clear polymer. The polymer material was selected so that its refractive index matched one of the principal refractive indices of the crystallites while the other did not. The resuit was a light polarizer tha t would pass one component of polarized light but scatter the other component out of the beam path.

This idea was substantially expanded by the introduction of liquid crystals as the birefringent material. The orientation of the particles (in this case droplets), and hence the refractive index match and the scattering, could be controlled by an electric field. Such a material could be used as a light shutter for either unpolarized or polarized light. In the mid-1970s this basic concept was applied by Hilsum, but having no way to disperse droplets of liquid crystals in a polymer, he did the opposite and put optically isotropic solid particles in the birefringent liquid crystal.

Although Hilsum demonstrated the concept, no commercial device was produced, probably because the shutter contrast was limited. Since then several ways have been found to disperse droplets in a polymer: filling the pores of a microfilter; emulsifying the liquid crystal in a water soluble polymer; and using phase separation methods to create a dispersion of droplets in non-aqueous polymer materials.

During the last few years, liquid crystalline elastomers (LCEs) have been systematically produced by cross-linking liquid crystalline side-chain polymers. In these networks, a liquid crystalline molecule is fixed at each monomeric unit. LCEs exhibit a novel combination of properties. Due to liquid crystalline groups, they show anisotropic liquid crystalline properties similar to conventional liquid crystals (LCs); but due to the three-dimensional network-structure of the polymer chains, they show typical elastomer properties, such as rubber elasticity or shape stability. One exceptional property of this combination is demonstrated when a mechanical deformation to the LCE causes macroscopically uniform orientation of the long molecular axis of the LC units (the so-called “director”).

This response of the LC-phase structure to an applied mechanical field is similar to the effect of electric or magnetic fields on low molecular weight liquid crystals (LMLC), as illustrated in Figure 1. Figure la shows an undeformed LCE. Because of the non-uniform orientation of the director, the sample scatters light strongly so the elastomer is translucent like frosted glass. On the other hand, applying a mechanical field the director becomes uniformly aligned and the sample is transparent (Figure 1b). Such a macroscopically ordered rubber exhibits optical properties very similar to single crystals. These propertie s of LCEs offer new prospects for technical application, e.g., in nonlinear and integrated optics.

In 1888, the year commonly taken as the birthdate of liquid crystal research, F. Reinitzer wrote to O. Lehmann to describe the curious properties of cholesteryl benzoate, a “substance [which] has two melting points, if it can be expressed in such a manner.” Throughout most of the 33°C interval between these two “melting points” this material is in the birefringent fluid state now known as the cholesteric liquid crystal. Today it is common to find compounds showing a whole cascade of liquid crystalline mesophases as the temperature is increased, but it is not customary to refer to any of the phase changes between them as “melting points” except for the lowest temperature transition where the crystalline lattice dissolves. In recent years, however, it has been discovered that many cholesteric liquid crystals, includin g cholesteryl benzoate, do something very strange in a temperature interval of only a degree or so just before they yield up their last bit of liquid crystalline order: they form complex structures having the symmetries of cubic lattices — they “freeze”! – and then “melt” at a higher temperature into either the ordinary amorphous liquid or else into a new kind of amorphous liquid which in turn undergoes a sharp transition into the ordinary amorphous liquid at still higher temperature.

Liquid crystals, discovered just a century ago, have wide application to electrooptic displays and thermography. Their physical properties have also made them fascinating materials for more fundamental research.

The name “liquid crystals” is actually a misnomer for what are more properly termed “mesophases,” that is, phases having symmetries intermediate between ordinary solids and liquids. There are three major classes of liquid crystals: nematics, smectics, and columnar mesophases. In nematics, although there is no correlation between positions of the rodlike molecules, the molecules tend to lie parallel along a common axis, labeled by a unit vector (or director) n. Smectics are more ordered. The molecules are also rodlike and are in layers. Different subtypes of smectics (labeled, for historical reasons, smectic A, smectic B,…) have layers that are more or less organized. In the smectic A phase, the layers are fluid and can glide easily over each other. In the smectic B phase, the layers have hexagonal ordering and strong interlayer corrélations. Indeed, the smectic B phase is more a highly anisotropic plastic crystal than it is a liquid crystal. Finally, columnar mesophases are obtained with disklike molecules. These molecules can stack up in columns which are themselves organized in a two-dimensional array. There is no positional correlation between molecules in one column and molecules in the other columns.

One hundred years after their discovery, we meet liquid crystals everywhere in our daily life. Their most widely known application is the liquid crystal displays (LCDs) in watches, pocket calculators, or gasoline pumps. Applications aside, liquid crystals show many exciting properties, making them highly interesting for fundamental research. For example, electrohydrodynamic convection (EHC) in nematic liquid crystals, which is studied in cells of a configuration similar to liquid crystal displays, serves with its characteristic properties as a model System for investigating central questions of pattern formation and chaos.

Today's liquid crystal displays work on the principle described in 1971 by Martin Schadt and Wolfgang Helfrich (Figure 1). In nematic liquid crystals, organic molecules orient on average along a macroscopic direction, described by the director field n(r), that has neither head nor tail (n = −n). Nematics are therefore anisotropic and for energetic reasons, n(r) orients parallel (perpendicular) to an electric field when the dielectric permittivity (ε∥) along n is larger (smaller) than the perpendicular (ε⊦ one. For positive εa = ε∥ − ε⊦, when an electric field is applied perpendicular to the direction of n, a reorientation of n takes place together with a corresponding change in the optical property of the cell. The controlled change by an electric field in the optic axis (orientation) in well-defined areas of the display then allows the representation of numbers, etc.