Traditional approaches to materials synthesis have largely relied on uniform, equilibrated phases leading to static “condensed-matter” structures (e.g., monolithic single crystals). Departures from these modes of materials design are pervasive in biology. From the folding of proteins to the reorganization of self-regulating cytoskeletal networks, biological materials reflect a major shift in emphasis from equilibrium thermodynamic regimes to out-of-equilibrium regimes. Here, equilibrium structures, determined by global free-energy minima, are replaced by highly structured dynamical states that are out of equilibrium, calling into question the utility of global thermodynamic energy minimization as a first-principles approach. Thus, the creation of new materials capable of performing life-like functions such as complex and cooperative processes, self-replication, and self-repair, will ultimately rely upon incorporating biological principles of spatiotemporal modes of self-assembly. Elucidating fundamental principles for the design of such out-of-equilibrium dynamic self-assembling materials systems is the focus of this issue of MRS Bulletin.

Nematic liquid crystals (NLCs) under micron-range confinement exhibit a rich defect phenomenology that can be used to extract elastic (Frank moduli) material parameters of critical importance for next generation electro-optical devices. In this work we develop a model to predict defect-driven textural transformations that arise when a NLC is confined to a circular capillary. In the initial transformation stage an unstable disclination defect of strength +1 nucleates in the axis of the capillary and quickly branches into two stable +1/2 disclination defects. The model includes: (1) the Kirchhoff branch balance equation which predicts the splitting of a +1 into two +1/2 wedge disclinations; (2) the curvature of the +1/2 disclination lines as a function of elastic properties. This model shows that by increasing the ratio of tension strength to bending stiffness, the branch point angle increases, but the final defect distance decreases; and (3) the aperture branching angle of the +1/2 lines as a function of the elastic properties and the magnitude of the curvature at the branch point. These three predictions form the basis for the evaluation of the Frank elastic moduli on NLCs. The key advantage of the implemented methodology is to use time-dependent textural transformations under micron-range capillary confinement to extract elastic parametric data needed to further develop NLCs in functional and structural application.

We have utilized the fact that syndiotactic and isotactic Poly(methyl methacrylate) {PMMA} form a stereocomplex to spin semi-crystalline PMMA fibers. Our goal is to produce oriented semi-crystalline fibers with a high enough melting point to withstand atactic-PMMA processing conditions. We successfully developed stereocomplex PMMA fibers by wet spinning and gel spinning, and characterized their properties by means of differential scanning calorimetry, optical/electron microscopy, mechanical testing and X-ray crystallography. Stereocomplex fibers from gel spinning have highest melting points and polymer chain orientation, hence are the best reinforcing agents. We are currently working on producing self-reinforced composites using these fibers.

Brilliant, iridescent colors found on the bodies and wings of many birds, butterflies and moths are produced by structural variations and have been the subject of study for centuries. Such brilliant colors have been described as metallic colors due to the saturation or purity of the color produced and have attracted the attention of great scientists like Newton, Michelson and Lord Rayleigh. It was recognized early on that such colors arise from physical effects such as interference or diffraction as opposed to colors that are normally produced due to the presence of chromophores which absorb or emit light. Common examples of physical colors are some butterfly wings [1], color of Indigo snake skin [2], hummingbird feathers [3,4], arthropod cuticles [which are due to selective reflection of color from the solidified cholesteric phase of chitin crystallites] [5], gemstones like opal [6,7], and some crystals like potassium chlorate [8]. While the origins of such colors are well understood the properties of color and color specification have not received much attention.

Often times one is asked the question "how can the optical microscope be used to make quantitative measurements?" The microscope certainly lets one observe the sample {whatever the sample may be) and make qualitative statements about what is it one is looking at. It has been used for various purposes from just visual observation in brightfield, reflection and the one that is near and dear to my heart, observations under crossed polarizers. This certainly allows one to identify materials as being isotropic or anisotropic. If one works on materials like liquid crystals, an optical microscope is a tool that is used all the time. It certainly allows for identification of various phases of liquid crystals based on the defects and textures that can be observed. All of this is somewhat qualitative in nature. By that I mean that the observations do not lend themselves to obtain, say for example, refractive index or birefringence of the material. I would like to describe a technique that will allow one to do just that.

Polymer-dispersed liquid crystal (PDLC) films are composed of micrometer-scale droplets of liquid crystal (typically nematic) in a polymeric matrix. They can be switched with an electric field from a scattering to a transparent state, and are of interest for use in flat-panel displays. The electro-optics of PDLC films, and the director field pattern within the nematic droplets, are strongly influenced by the surface anchoring condition at the liquid crystal - polymer matrix interface. To understand the role of surface anchoring, we studied the electro-optics of photopolymerized PDLC films composed of a liquid crystal and acrylates as a function of temperature. Properties depend strongly upon the choice of the acrylate. With several acrylate matrix materials, the nernatic director field undergoes a reversible, temperature-driven configurational transition, accompanied by dramatic changes in electro-optical properties. We find that the surface anchoring behavior is very sensitive to the polymer structure as well as several parameters of PDLC film formation. Several surface anchoring transitions are used in a study that shows strong evidence for surface memory in PDLC films.

Rheo-optical studies on aligned and unaligned melts of a main chain thermotropic polyester with flexible spacers are discussed in terms of the predictions of the Ericksen-Leslie equations. It is shown, using conoscopy, that the director is flowaligning at temperatures close to TNI and nonflow-aligning close to a smectic to nematic (TSN) phase transition. The implications of these results are discussed in terms of the change in sign of one of the Leslie viscosity coefficients and interpreted in the framework of the Ericksen-Leslie Theory.