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Spherulites are radial distributions of acicular crystals, common in biogenic, geologic, and synthetic systems, yet exactly how spherulitic crystals nucleate and grow is still poorly understood. To investigate these processes in more detail, we chose scleractinian corals as a model system, because they are well known to form their skeletons from aragonite (CaCO3) spherulites, and because a comparative study of crystal structures across coral species has not been performed previously. We observed that all 12 diverse coral species analyzed here exhibit plumose spherulites in their skeletons, with well-defined centers of calcification (CoCs), and crystalline fibers radiating from them. In 7 of the 12 species, we observed a skeletal structural motif not observed previously: randomly oriented, equant crystals, which we termed "sprinkles". In Acropora pharaonis, these sprinkles are localized at the CoCs, while in 6 other species, sprinkles are either layered at the growth front (GF) of the spherulites, or randomly distributed. At the nano- and micro-scale, coral skeletons fill space as much as single crystals of aragonite. Based on these observations, we tentatively propose a spherulite formation mechanism in which growth front nucleation (GFN) of randomly oriented sprinkles, competition for space, and coarsening produce spherulites, rather than the previously assumed slightly misoriented nucleations termed "non-crystallographic branching". Phase-field simulations support this mechanism, and, using a minimal set of thermodynamic parameters, are able to reproduce all of the microstructural variation observed experimentally in all of the investigated coral skeletons. Beyond coral skeletons, other spherulitic systems, from aspirin to semicrystalline polymers and chocolate, may also form according to the mechanism for spherulite formation proposed here. STATEMENT OF SIGNIFICANCE: Understanding the fundamental mechanisms of spherulite nucleation and growth has broad ranging applications in the fields of metallurgy, polymers, food science, and pharmaceutical production. Using the skeletons of reef-building corals as a model system for investigating these processes, we propose a new spherulite growth mechanism that can not only explain the micro-structural diversity observed in distantly related coral species, but may point to a universal growth mechanism in a wide range of biologically and technologically relevant spherulitic materials systems.

We report the phase behavior of amorphous/semicrystalline conjugated polymer blends composed of low bandgap poly[2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [2,1-b, 3,4-b&prime, ]dithiophene) -alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT) and poly{(N,N&prime, bis(2-octyldodecyl)naphthalene -1,4,5,8-bis(dicarboximide)-2,6-diyl)-alt-5,5&prime, (2,2&prime, bithiophene)} (P(NDI2OD-T2)). As usual in polymer blends, these two polymers are immiscible because &Delta, Sm &asymp, 0 and &Delta, Hm &gt, 0, leading to &Delta, Gm &gt, 0, in which &Delta, Sm, &Delta, Hm, and &Delta, Gm are the entropy, enthalpy, and Gibbs free energy of mixing, respectively. Specifically, the Flory&ndash, Huggins interaction parameter (&chi, ) for the PCPDTBT /P(NDI2OD-T2) blend was estimated to be 1.26 at 298.15 K, indicating that the blend was immiscible. When thermally analyzed, the melting and crystallization point depression was observed with increasing PCPDTBT amounts in the blends. In the same vein, the X-ray diffraction (XRD) patterns showed that the &pi, &pi, interactions in P(NDI2OD-T2) lamellae were diminished if PCPDTBT was incorporated into the blends. Finally, the correlation of the solid-liquid phase transition and structural information for the blend system may provide insight for understanding other amorphous/semicrystalline conjugated polymers used as active layers in all-polymer solar cells, although the specific morphology of a film is largely affected by nonequilibrium kinetics.

International audience; In the present work, we propose the synthesis of a new family of sugar derived 1,4:3,6-dianhydrohexitol based AA/AB-type monomers. Unprecedented diacids based on Isomannide and Isoidide were elaborated with high yields and showed interestingly high melting point ranges (240-375 degrees C). Optimization of reaction conditions (temperature, time of reaction, and reactant ratios) has been investigated to synthesize the key intermediate of a set of AB monomers with acid, ester, and acid chloride functionalities. Isosorbide based ether benzoic acid AB monomer was polymerized and characterized by NMR and DSC techniques. The results show a semicrystalline behavior of the obtained polymer thanks to the controlled stereoregular arrangement of the AB starting monomer.

A waterborne latex-based technique, in which functionalized laponite is attached to PS and acrylic latex particles, is used to prepare films containing up to 50 wt% laponite. At high laponite contents this leads to a cellular arrangement of the laponite-rich layers, concentrated at the latex particle interfaces. MDSC shows that a significant proportion of the organic matrix does not contribute to the glass transition. However, this "rigid" matrix fraction arises from intercalation of the laponite stacks, and cannot account for the large increases in global stiffness in the rubbery state (T> T g) on laponite addition. The mechanical response for T> T g is therefore discussed in terms of a four-phase structure, in which the intercalated laponite stacks embedded in a matrix with a relatively high rubbery modulus form a cellular structure, which is in turn embedded in a matrix whose modulus is closer to that of the bulk polymer. The importance of the cellular arrangement is underlined by the much lower rubbery modulus observed by DMA in specimens produced by deforming the original films in plane strain compression to produce oriented textures with relatively little connectivity between the laponite-rich layers. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

A waterborne latex-based technique has been used to prepare acrylic films with laponite contents up to about 25 vol%. The laponite was attached to the surfaces of the latex particles, giving a cellular arrangement of laponite-rich regions at high laponite contents. Two regimes of reinforcement were observed, depending on whether T was above or below T-g, reinforcement at T > T-g being significantly greater than predicted by micromechanical models. Modulated differential scanning calorimetry and dynamic mechanical analysis showed part of the organic content of the films not to contribute to the glass transition. This "rigid amorphous fraction" (RAF) was argued to correspond to intercalated regions of the matrix. However, the RAF alone was insufficient to account for the observed increases in stiffness at T > T-g. The mechanical response is therefore discussed in terms of a four-phase model, in which intercalated laponite stacks are embedded in a matrix with reduced mobility, forming a foam-like structure, in turn embedded in a matrix with the properties of the bulk polymer. (C) 2011 Elsevier Ltd. All rights reserved.

Structural complexity inherited from a microbial synthesis of glycolipids was translated into unique poly(sophorolipid) biomaterials. ROMP polymerization of natural diacetylated lactonic sophorolipids gave a high molecular weight polymer with asymmetric bola-amphiphilic repeating units. The poly(sophorolipid) chain alternates C18 oleic-like aliphatic segments (90% cis-configured double bonds) with bulky diacetylated disaccharide moieties. The solid-state properties were investigated by means of TGA, DSC, TMDSC, and variable-temperature X-ray diffraction. The poly(sophorolipid) is a solid at room temperature that undergoes the glass transition at 61 degrees C and melts at 123 degrees C. The crystal phase is associated with ordered packing of the aliphatic chain segments. The semicrystalline poly(sophorolipid) also displays a long-range order (d = 2.44 nm) involving sophorose groups that is found to persist after crystal phase melting (in high-T diffractograms) with a slightly shortened distance (2.27 nm). Upon annealing at 80 degrees C the poly(sophorolipid) recrystallizes and concomitantly the disaccharide units space out again at 2.44nm. An exothermal phenomenon that immediately follows melting and is revealed by TMDSC might be associated with the observed adjustment of sophorose units spacing in the melt. The peculiar structural organization of this novel biomaterial is discussed.

Polyolefins, semicrystalline polymers also known as thermoplastics, are highly desirable because of their material properties, low cost, and ease in processing. The flow and thermal history experienced during processing are known to affect dramatic changes in crystalline kinetics and morphology, dictating the final material properties of solidified products. However, the underlying physics that control crystalline orientation and kinetics is not well understood. To optimize processing conditions and maximize material performance, it is desirable to understand how the interplay of molecular character and flow conditions shape crystalline microstructure. In the last decade, advances in catalyst technology have produced well defined materials enabling the systematic study of molecular influences on flow-induced crystallization. We investigate bimodal blends of polypropylenes (PP) in which we vary the molecular character (concentration, molecular weight, regularity) of the high molecular weight mode. We apply a number of in situ characterization tools (rheo-optics, rheo-WAXD) to the development of transient structure and interpret our findings in light of ex situ examination (polarized light microscopy, TEM) of the final morphology. Blending a well-characterized high molecular weight isotactic polypropylene into a "base iPP" at various concentrations (c), we determined that blends with less than 1% of chains with Mw five times larger than the Mw of the base resin profoundly affected the crystallization kinetics and crystalline morphology of a sheared melt. Beyond unambiguously demonstrating the important role of long chains in the formation of anisotropic crystallization under flow, this approach allowed us to be specific about the length that is meant by "long chains" and the concentration of these chains in the melt. Varying the concentration from below to above c* revealed that the effect of the long chains involves cooperative interactions, evident in the non-linear relationship of the long chain concentration, particularly as c approaches the long chain-long chain overlap concentration. The long chains greatly enhance the formation of threadlike precursors but only mildly enhance the formation of pointlike precursors. In studying a series of blends in which the Mw of the long chain mode was varied, we found that increasing the Mw of the long chain portion of a bimodal blend increased the tendency to form threadlike precursors to oriented crystallization. This was highlighted by a marked decrease in the threshold stress necessary to induce oriented crystalline growth and is related to the separation in time scales between the slowest relaxing chains and the average. Thus, the propagation of shish varies strongly with the separation in time scales between the slowest relaxing chains and the average. Below a threshold ratio of relaxation times (tau_L/tau_S ~ 100) addition of long chains did not change the behavior from that of Base-PP itself. Our analysis of real-time rheo-optical and rheo-WAXD experiments combined with depth dependent information from a novel "depth sectioning" analysis technique uncovers several keys to understanding how anisotropic crystallization is induced by flow. Threads first form near the channel wall, where stress is highest, and grow in length with prolonged flow. After sufficient time, thread length per unit volume saturates, perhaps due to collisions with other threads or crystalline overgrowth from those threads. Prior to saturation, when crystalline overgrowth is negligible, the thread propagation appears to be linear with shearing time. The propagation of threads varies in a nonlinear manner with stress. Finally, we identify a promising set of conditions that can be used to measure the thread propagation velocity for this material if the appropriate length scale can be assigned by microscopy. We examined the effects of long chain regularity on the formation of threadlike precursors, showing that addition of molecular level defects to the high end of the molecular weight distribution effectively raises the threshold stress and mitigates the formation of oriented precursors induced by flow. Our study included a model bimodal blend of isotactic and atactic polypropylene as well as large scale bimodal blends of isotactic polypropylene and a propylene-ethylene copolymer fit for pilot-scale production of nonwoven fabrics. It is noteworthy that the qualitative behavior observed in the melt-spinning process accords well with the trends evident in isothermal shear-induced crystallization. This has value in two respects. Scientifically, it is significant that idealized flow and thermal conditions may well reveal the physics relevant to polymer processing, which involves mixed shear and extension under non-isothermal conditions. Technologically, the ability to screen different resin compositions on a small scale can be used to optimize flow-induced crystallization characteristics prior to scale up.

Solution-processable semiconducting polymers have been explored over the last decades for their potential applications in inexpensively fabricated transistors, diodes and photovoltaic cells. However, a remaining challenge in the field is to control the solid-state self-assembly of polymer chains in thin films devices, as the aspects of (semi)crystallinity, grain boundaries, and chain entanglement can drastically affect intra-and inter-molecular charge transport/transfer and thus device performance. In this short review we examine how the aspects of molecular weight and chain rigidity affect solid-state self-assembly and highlight molecular engineering strategies to tune thin film morphology. Side chain engineering, flexibly linking conjugation segments, and block co-polymer strategies are specifically discussed with respect to their effect on field effect charge carrier mobility in transistors and power conversion efficiency in solar cells. Example systems are taken from recent literature including work from our laboratories to illustrate the potential of molecular engineering semiconducting polymers.