Sugar-Based Polyamides: Self-Organization in Strong Polar Organic Solvents.

Periodic patterns resembling spirals were observed to form spontaneously upon unassisted cooling of d-glucaric acid- and d-galactaric acid-based polyamide solutions in N-methyl-N-morpholine oxide (NMMO) monohydrate. Similar observations were made in d-galactaric acid-based polyamide/ionic liquid (IL) solutions. The morphologies were investigated by optical, polarized light and confocal microscopy assays to reveal pattern details. Differential scanning calorimetry was used to monitor solution thermal behavior. Small- and wide-angle X-ray scattering data reflected the complex and heterogeneous nature of the self-organized patterns. Factors such as concentration and temperature were found to influence spiral dimensions and geometry. The distance between rings followed a first-order exponential decay as a function of polymer concentration. Fourier-Transform Infrared Microspectroscopy analysis of spirals pointed to H-bonding between the solvent and the pendant hydroxyl groups of the glucose units from the polymer backbone. Tests on self-organization into spirals of ketal-protected d-galactaric acid polyamides in NMMO monohydrate confirmed the importance of the monosaccharide's pendant free hydroxyl groups on the formation of these patterns. Rheology performed on d-galactaric-based polyamides at high concentration in NMMO monohydrate solution revealed the optimum conditions necessary to process these materials as fibers by spinning. The self-organization of these sugar-based polyamides mimics certain biological materials.

Design of a humidity controlled sample stage for simultaneous conductivity and synchrotron X-ray scattering measurements.

We report on the design and operation of a novel sample stage, used to simultaneously measure X-ray scattering profiles and conductivity of a polymer electrolyte membrane (PEM) surrounded by humid air as a function of temperature and relative humidity. We present data obtained at the Advanced Light Source and Stanford Synchrotron Radiation Laboratory. We demonstrate precise humidity control and accurate determination of morphology and conductivity over a wide range of temperatures. The sample stage is used to study structure-property relationships of a semi-crystalline block copolymer PEM, sulfonated polystyrene-block-polyethylene.

Morphology and thermodynamic properties of a copolymer with an electronically conducting block: poly(3-ethylhexylthiophene)-block-poly(ethylene oxide).

We report on the synthesis and morphology of a block copolymer, poly(3-(2'-ethylhexyl)thiophene)-b-poly(ethylene oxide) (P3EHT-b-PEO), that conducts both electrons and ions. We show that in the melt state the P3EHT-b-PEO chains self-assemble to produce traditional nanoscale morphologies such as lamellae and gyroid. This is in contrast to a majority of previous studies on copolymers with electronically conducting blocks wherein a nanofibrillar morphology is obtained. Our approach enables estimation of the Flory-Huggins interaction parameter, χ. The segregation strength between the two blocks is controlled through the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). For the salt-free sample, the gyroid morphology, obtained in the melt state, is transformed into lamellae below the melting temperature of the P3EHT block. This is due to the "breaking out" of the crystalline phase. For the salt-containing sample, P3EHT-b-PEO has a lamellar morphology in both melt and crystalline states (confined crystallization).

Langmuir monolayers of straight-chain and branched hexadecanol and eicosanol mixtures.

Langmuir monolayers of straight-chain and branched hexadecanol and eicosanol mixtures were previously studied using surface pressure- area isotherms, Brewster angle microscopy, and interfacial rheology. In this paper, we investigate the structure of these fatty alcohol mixtures using these previous results together with X-ray diffraction and reflectivity measurements, which provide a better understanding of the structure of the monolayer in terms of the phase segregation and location of branched chains. For eicosanol below 25 mN/m, the branched chains are incorporated into the monolayer, yet they are phase-separated from the straight chains. At higher surface pressures, the branched chains are expelled from the monolayer and presumably form micelles or some other aggregate in the subphase. In contrast, the hexadecanol branched chains are not present in the monolayer at any surface pressure. These behaviors are interpreted with the help of the X-ray measurements and density profiles, and are explained in terms of straight-chain flexibility. We will discuss the effect of the monolayer structure on the surface shear viscosity. These studies provide a deeper understanding of the structure and behavior of amphiphilic mixtures, and will ultimately aid in developing models for lipids, micelle formation, and other important biological functions.

Diffusion of dextran probes in a self-assembled fibrous gel composed of two-dimensional arborols.

Two-dimensional arborols are bolaform amphiphiles in which a central, hydrophobic spacer separates twin hydrophilic ends. Under appropriate conditions, these relatively small molecules assemble into very long fibers; subsequently, the system gels if the arborol concentration is sufficiently high. The diffusion of linear or slightly branched dextran probes in 3 and 6% arborol gels, as determined by fluorescence photobleaching recovery, resembles that of dextrans in water, suggesting a highly open network structure. Melting the gels produces almost no change in diffusion of the dextran probes. Small-angle X-ray scattering (SAXS) of wet arborol gels at different concentrations and temperatures reveals the diameter of the repeating unit of the fibers to be 8.26+/-0.68 nm. This dimension, which is independent of concentration and temperature, exceeds the length of a single arborol molecule by about a factor of 3. Rheological investigation identifies the linear response regime of the gels and permits an examination of the weak correlation between dextran probe diffusion and gel viscoelasticity.

Synchrotron and simulations techniques applied to problems in materials science: catalysts and Azul Maya pigments.

Development of synchrotron techniques for the determination of the structure of disordered, amorphous and surface materials has exploded over the past 20 years owing to the increasing availability of high-flux synchrotron radiation and the continuing development of increasingly powerful synchrotron techniques. These techniques are available to materials scientists who are not necessarily synchrotron scientists through interaction with effective user communities that exist at synchrotrons such as the Stanford Synchrotron Radiation Laboratory. In this article the application of multiple synchrotron characterization techniques to two classes of materials defined as 'surface compounds' is reviewed. One class of surface compounds are materials like MoS(2-x)C(x) that are widely used petroleum catalysts, used to improve the environmental properties of transportation fuels. These compounds may be viewed as 'sulfide-supported carbides' in their catalytically active states. The second class of 'surface compounds' are the 'Maya blue' pigments that are based on technology created by the ancient Maya. These compounds are organic/inorganic 'surface complexes' consisting of the dye indigo and palygorskite, common clay. The identification of both surface compounds relies on the application of synchrotron techniques as described here.

Responsive solids from cross-linked block copolymers.

Novel responsive solids were prepared by randomly cross-linking the polyisoprene chains of a disordered polystyrene-polyisoprene block copolymer. Our experiments show that block copolymer chains, composed of hundreds of repeat units, can undergo reversible order-disorder transitions despite the quenched randomness that arises due to the attachment of one of the blocks to a cross-linked network. The structure, properties, and phase behavior of these materials are determined by a delicate interplay between the density of cross-links and the nature of the ordered state.

Quantum Chemical Models (Nobel Lecture).

The solving of chemical problems to which the answer is unknown or in dispute is the important objective of each theoretical model. How far quantum chemistry has come in this respect is described here for the ab initio concept, which is known to just about every chemist under the name GAUSSIAN. The major advantage of this method is that it can be used to define a way in which one can obtain more accurate results. The target of calculating binding energies and similar values with precisions of 1 kcal mol-1 is not far away for small molecules containing up to fifty electrons.