1 Based on observations obtained with the Spitzer Space Telescope, which is operated by JPL, CalTech, under NASA Contract 1407.

A novel bottom-up approach to obtain polymer nanocomposites using cubic silsesquioxanes (POSS) nanoparticles as building blocks is reported. The design is based on associative interaction between particles to form ordered nanostructure and limited crystal growth to render anisotropic shapes. Specifically, the affinity between POSS units causes these particles to aggregate and closely pack into a crystalline lattice. The organic polymer, covalently connected to each POSS unit, limits the crystallization into a two-dimensional lattice as demonstrated in random copolymers of polybutadiene and cubic silsesquioxanes. The copolymers were synthesized by ring-opening metathesis copolymerization of cyclooctadiene and POSS bearing a polymerizable norbornene group. The polymers were characterized using NMR, DSC, TEM, WAXD, and SAXS. The data from TEM and X-ray diffraction clearly show the formation of two-dimensional lamellar-like nanostructures of assembled cubic silsesquioxanes.

Compared to starburst galaxies, normal star forming galaxies have been shown to display a much larger dispersion of the dust attenuation at fixed reddening through studies of the IRX-β diagram (the IR/UV ratio "IRX" versus the UV color "β"). To investigate the causes of this larger dispersion and attempt to isolate second parameters, we have used GALEX UV, ground-based optical, and Spitzer infrared imaging of 8 nearby galaxies, and examined the properties of individual UV and 24 µm selected star forming regions. We concentrated on star-forming regions, in order to isolate simpler star formation histories than those that characterize whole galaxies. We find that 1) the dispersion is not correlated with the mean age of the stellar populations, 2) a range of dust geometries and dust extinction curves are the most likely causes for the observed dispersion in the IRX-beta diagram 3) together with some potential dilution of the most recent star-forming population by older unrelated bursts, at least in the case of star-forming regions within galaxies, 4) we also recover some general characteristics of the regions, including a tight positive correlation between the amount of dust attenuation and the metal content. Although generalizing our results to whole galaxies may not be immediate, the possibility of a range of dust extinction laws and geometries should be accounted for in the latter systems as well.

We report the discovery of a large-scale structure containing multiple protoclusters at z = 3.78 in the Boötes field. The spectroscopic discovery of five galaxies at z = 3.783±0.002 lying within 1 Mpc of one another led us to undertake a deep narrow-and broad-band imaging survey of the surrounding field. Within a comoving volume of 72 × 72 × 25 Mpc 3 , we have identified 65 Lyman alpha emitter (LAE) candidates at z = 3.795 ± 0.015, and four additional galaxies at z spec = 3.730, 3.753, 3.780, 3.835. The galaxy distribution within the field is highly non-uniform, exhibiting three large (≈ 3 − 5×) overdensities separated by 8 − 14 Mpc (physical) and possibly connected by filamentary structures traced by LAEs. The observed number of LAEs in the entire field is nearly twice the average expected in field environments, based on estimates of the Lyα luminosity function at these redshifts. We estimate that by z = 0 the largest overdensity will grow into a cluster of mass ≈ 10 15 M ⊙ ; the two smaller overdensities will grow into clusters of mass (2 − 6) × 10 14 M ⊙ . The highest concentration of galaxies is located at the southern end of the image, suggesting that the current imaging may not map the true extent of the large scale structure. Finding three large protocluster candidates within a single 0.3 deg 2 field is highly unusual; expectations from theory suggest that such alignments should occur less than 2% of the time. Searching for and characterizing such structures and accurately measuring their volume space density can therefore place constraints on the theory of structure formation. Such regions can also serve as laboratories for the study of galaxy formation in dense environments.

We present new observations of the field containing the z = 3.786 protocluster, PC 217.96+32.3. We confirm that it is one of the largest and most overdense high-redshift structures known. Such structures are rare even in the largest cosmological simulations. We used the Mayall/MOSAIC1.1 imaging camera to image a 1.2 • × 0.6 • area (≈ 150 × 75 comoving Mpc) surrounding the protocluster's core and discovered 165 candidate Lyα emitting galaxies (LAEs) and 788 candidate Lyman Break galaxies (LBGs). There are at least 2 overdense regions traced by the LAEs, the largest of which shows an areal overdensity in its core (i.e., within a radius of 2.5 comoving Mpc) of 14 ± 7 relative to the average LAE spatial density (ρ) in the imaged field. Further,ρ is twice that derived by other field LAE surveys. Spectroscopy with Keck/DEIMOS yielded redshifts for 164 galaxies (79 LAEs and 85 LBGs); 65 lie at a redshift of 3.785 ± 0.010. The velocity dispersion of galaxies near the core is σ = 350 ± 40 km s −1 , a value robust to selection effects.The overdensities are likely to collapse into systems with present-day masses of > 10 15 M ⊙ and > 6 × 10 14 M ⊙ . The low velocity dispersion may suggest a dynamically young protocluster. We find a weak trend between narrow-band (Lyα) luminosity and environmental density: the Lyα luminosity is enhanced on average by 1.35× within the protocluster core. There is no evidence that the Lyα equivalent width depends on environment. These suggest that star-formation and/or AGN activity is enhanced in the higher density regions of the structure. PC 217.96+32.3 is a Coma cluster analog, witnessed in the process of formation.

A small mass concentration of poly(benzyl ether) dendrimer added to a low molecular mass polystyrene is found to inhibit the dewetting of a thin (≈50 nm) polystyrene film from an acid-etched silicon substrate. The inhibition effect is found to depend on generation number where the lowest generation (G ) 3) tested was the most effective. Our findings are qualitatively similar to previous observations by Barnes et al. [Macromolecules 2000, 33, 4177-4185.] where the addition of fullerenes ("buckyballs", C60) similarly inhibited the dewetting of thin polystyrene and polybutadiene films. Thus, dewetting inhibition by nanoparticles appears to be a general effect, although certain conditions apparently need to be met for its occurrence. Specifically, a general tendency for the particles to segregate to the solid substrate seems to be required and the interaction between the particles and polymer must not be too unfavorable. The phase boundaries of the dendrimer-polymer mixtures depend on the generation, the higher generation being more miscible in terms of mass fraction. This suggests that the driving force for the dendrimer to segregate to the boundary is varied by changing the generation number, thus giving rise to a dendrimer generational effect on dewetting suppression.

A morphological study of three I5S six-arm miktoarm star block copolymers is presented. These miktoarm stars are comprised of five arms of polyisoprene (PI) and one arm of polystyrene (PS) joined together at a single junction point. The strong segregation limit theory for the morphological behavior of miktoarm stars predicts that these materials should form spherical morphologies, but only lamellar and cylindrical morphologies were observed by TEM and SAXS. These results are similar to previously reported discrepancies between experimentally observed morphological behaviors of miktoarm stars and the predictions of the theory. Previous work has attributed the discrepancies to the neglect of the effect of the multifunctional junction points on calculated free energies. The current results suggest that, in addition to this, geometrical packing constraints prevent the formation of morphologies such as spheres and cylinders in highly asymmetric miktoarm stars in which the minor volume fraction component would need to occupy the matrix phase. Finally, unusual broken chevron tilt grain boundary morphologies were observed in a lamellar I 5S material. We attribute these new structures to the asymmetric energy penalties for interfacial bending which result from the molecular asymmetry of the miktoarm stars.

The bulk morphology of a crystalline/amorphous diblock copolymer under different thermal conditions was studied. The diblock copolymer, poly((ethylene oxide)-b-1,4-polybutadiene), forms a microphase-separated lamellar morphology in the molten state. For samples crystallized within the range of 20−50 °C, TEM coupled with electron diffraction revealed a microphase-separated, alternating lamellar morphology with the PEO crystalline chains oriented perpendicular to the interface between the PEO and PBD domains. A significant increase in the microphase-separated, lamellar domain spacing was observed upon crystallization. On the length scale of tens of microns, as probed by polarizing optical microscopy, a nonspherultic crystalline texture (with the absence of the Maltese cross), corresponding to the microphase-separated lamellar grain morphology, was observed. In contrast to the integral chain folding observed in PEO homopolymer, the increase in PEO lamellar thickness with decreasing undercooling is continuous in the block copolymer. In addition, the equilibrium melting temperature and lamellar spacing were determined.