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High-speed light emitters integrated on silicon chips can enable novel architectures for silicon-based optoelectronics, such as on-chip optical interconnects, and silicon photonics. However, conventional light sources based on compound semiconductors face major challenges for their integration with a silicon-based platform because of their difficulty of direct growth on a silicon substrate. Here we report ultra-high-speed (100-ps response time), highly integrated graphene-based on-silicon-chip blackbody emitters in the near-infrared region including telecommunication wavelength. Their emission responses are strongly affected by the graphene contact with the substrate depending on the number of graphene layers. The ultra-high-speed emission can be understood by remote quantum thermal transport via surface polar phonons of the substrates. We demonstrated real-time optical communications, integrated two-dimensional array emitters, capped emitters operable in air, and the direct coupling of optical fibers to the emitters. These emitters can open new routes to on-Si-chip, small footprint, and high-speed emitters for highly integrated optoelectronics and silicon photonics., Integrating graphene with existing silicon technologies may pave the way to compact light sources for optoelectronics and photonics. Here, the authors fabricate graphene-based arrays of blackbody emitters integrated on a silicon chip, operating in the near-infrared region at high speed.

In nature, biological macromolecules control the growth of inorganic crystals under mild conditions in aqueous media. Inspired by biomineralization, biomimetic approaches have been studied for growth control of inorganic crystals in aqueous media by using organic molecules and polymers. The approaches were not applied to nonaqueous systems for the development of functional organic materials. Here, we have applied biomimetic approaches to growth control of organic crystals in nonaqueous media. Morphology and orientation of 10,12-pentacosadiynoic acid (PCDA) crystals, a diacetylene derivative, were controlled in organic media with the additive organic polymers and surface-modified substrates. The oriented PCDA ribbons were obtained by an advanced biomimetic approach. After topochemical polymerization, the resultant polydiacetylenes (PDA) ribbons were applied to the thermochromic materials with intercalation of metal ions and the semiconductor layer of an organic field-effect transistor. The present work imp...

Synthesis, recyclability, and physical properties of poly( l -lactide) (PLLA)-based network polymers prepared by means of Diels–Alder (DA) reaction between bisfuranic terminated PLLA prepolymers (PLLAnF2-x; degree of polymerization, n = 35–59, substituent in the vicinity of furan, x = amide or ester) and a tris-maleimide cross-linker (M3) are described. Molecular weight of prepolymer and substituent in the vicinity of furan rings are strongly effective in equilibrium control of DA and retro-DA reactions between PLLAnF2-x and M3. Lower molecular weight of the prepolymer and amide-substitution in the vicinity of furans significantly enhance the reactivity between PLLAnF2-x and M3, resulting in more perfect network structure, completely suppressed crystallinity, and much better mechanical properties of the PLLA-based DA network polymers. The PLLA-based DA network polymer containing numerous thermoreversible covalent bonds is a promising material as a readily recyclable biobased polymeric material.

A series of multiblock polyurethanes with alternating sequence structures of a poly(e-caprolactone) (PCL)

Organic near-infrared photorefractive molecular glasses with a phenothiazine moiety are designed and synthesized through the introduction of linear, racemic/homochiral asymmetrically branched aliphatic chains into photorefractive chromophore as an auxiliary group. The compounds are characterized with 1H-NMR, IR, FAB-MS, UV-vis, TG, DSC, etc. The effect of different aliphatic chains on the absorption and thermal properties is investigated in detail. The molar absorption coefficiency at the absorption maximum wavelength showed that the homochiral asymmetrically branched aliphatic chain has a strong hypochromic effect in the dilute solution when it is introduced into photorefractive chromophore. The DSC measurement indicated that the introduction of asymmetrically branched aliphatic chain is the key issue to design organic molecular glasses whether it is racemic or homochiral. The effect of racemic/homochiral asymmetrically branched aliphatic groups on photorefractive property is investigated carefully with poly(N-vinylcarbazole) (PVK) as a photoconductor and with (2,4,7-trinitro-9-fluorenylidene) malononitrile (TNFM) as a photosensitizer. The results suggested that the racemic group is more beneficial to the improvement of photorefractive performance than the homochiral when the homochiral cannot induce rigid photorefractive chromophore to be much more ordered. 2012 Elsevier Ltd. All rights reserved.

A network polymer with photoinduced mending abilities was prepared from cinnamoyl-telechelic prepolymer of poly(butylene adipate), PBAC2, and a tetra-cinnamoyl linker, C4, by photodimerization. The photodimerization reaction of the cinnamoyl groups was analyzed using both ultraviolet (UV)/visible (vis) and infrared (IR) spectroscopy. In the reaction, the isomerization of the cinnamate group from the trans to the cis conformation competes with the dimerization reaction of cinnamates. The fractions of dimer and isomer populations estimated from the UV/vis spectra revealed that dimerization was the more preferred reaction at temperatures higher than the melting point of PBAC2. When a film of the network polymer was damaged by tapping, the cinnamate dimers dissociated to form cinnamate monomers due to the reversibility of the dimerization. To recover the network structure, these monomers could be dimerized once again through a photoirradiation process. These results show that cracks in the network polymer can be recovered through photoirradiation. A network polymer with photoinduced mending ability is prepared from a cinnamoyl-telechelic prepolymer and a tetra-cinnamoyl linker by photodimerization. Though the trans–cis isomerization competes with the dimerization of cinnamates, the dimerization primarily proceeds at a temperature higher than the melting point of the prepolymer. When a film of the network polymer is damaged, cinnamate dimers in the polymer are dissociated to form cinnamate monomers. These monomers can be dimerized again by photoirradiation to recover the network structure.

In this work, a novel soft shape memory polymer nanocomposite derived from a bacterial medium-chain-length polyhydroxyalkanoate, poly(3-hydroxyoctanoate-co-3-hydroxyundecenoate) (PHOU), used to form a covalent network grafted with polyhedral oligomeric silsesquioxane (POSS), a crystallizable inorganic–organic hybrid nanofiller, was prepared. The PHOU–POSS nanocomposite, PHOU–POSSw-net [w (= POSS content, wt %) = 0, 20, 25, 30, and 38], is a completely amorphous elastomer (w ≤ 20) or contains POSS nanocrystals embedded in the amorphous PHOU matrix (w ≥ 25). The hybrid nanostructure of PHOU–POSSw-net (w ≥ 25) is featured by its reconfigurability, based on aggregation and disaggregation of POSS covalently connected to the PHOU network, which enables excellent shape fixing and recovery. Furthermore, it exhibits soft and elastomeric mechanical properties even in the fixed state. Taking advantage of the shape memory ability as well as the softness in the fixed state, we demonstrate microscale dynamic surface topography of PHOU–POSSw-net. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012

Remending properties of a network polymer with reversible reactivity are described. The network structure is constructed by a Diels–Alder (DA) reaction between furyl-telechelic poly(ethylene adipate) (PEAF 2 ) and a tris-maleimide, M 3 . When a film sample was cut into two pieces and the cut surfaces were kept in contact with each other at 60 °C, rejoining of the cut pieces was observed. This mending was induced by the reversible cross-linking reaction bridging the cut surfaces. At the cut front, the “weak” DA adducts are selectively dissociated sacrificially to release the stress so as to protect the chemical structure of the prepolymer and the linker against the scission or degradation. The dissociated furan and maleimide readily reconnect by forward DA reaction to mend the material. The remending was also observed for the samples kept at room temperature after melting at 60 °C. So, the PEAF 2 network polymer is a thermo-responsive mendable material in which crack healing is induced by a prompt thermal stimulus.

A series of hard−soft convertible network polymers were obtained using Diels−Alder reaction between semicrystalline prepolymers, furyl-telechelic poly(e-caprolactone) with number-averaged molecular weights ranging from 2450 to 8800 (PCLnF2; n (degree of polymerization) = 18, 22, 26, 33, and 74), and a tris-maleimide linker (M3). The reaction between PCLnF2 and M3 was conducted in the semicrystalline state or in the molten state, resulting in two different cross-linked polymers exhibiting harder and softer mechanical properties, respectively (PCLnF2M3-CRY1st and PCLnF2M3-CL1st). The difference in the properties can be attributed to the difference in size and order of crystalline domains for n ≥ 22 and that in degree of crystallinity for n = 18. The network polymers exhibit the hard−soft conversion behavior via melt/recrystallization process without de-cross-linking. The molecular weight of PCLnF2 strongly affects this hard−soft conversion.

A semicrystalline cross-linked polymer exhibiting two-way conversion between totally different mechanical properties was obtained. Furyl-telechelic poly(1,4-butylene succinate-co-1,3-propylene succinate) prepolymer (PBPSF2) was prepared and polymerized with tris-maleimide linker (M3) by the Diels−Alder (DA) reaction in the bulk state. The DA reactions with M3 above and below the melting temperature of PBPSF2 gave network polymers with relatively soft and hard properties, respectively, though the degrees of crystallinity of them were very similar. The large difference in mechanical properties was attributed to the difference in size of crystallites. By combining the two dynamic processes of melt−recrystallization and depolymerization−repolymerization, we can freely convert the PBPSF2 + M3 system back and forth between hard and soft materials.

Crystallization behavior was investigated for poly(butylene succinate)-based ionomers (PBSIs) with very small amounts of metal sulfosuccinate units. The PBSI samples, precipitated by adding their chloroform solutions into an excess volume of hexane, showed not only higher overall crystallization rates than the parent PBS but also strong fusion temperature dependences of the crystallization kinetics. In the early stage of film-hydrolysis experiments, the center region of PBSI spherulites was found to be easily eroded. A putative internal structure of PBSI spherulites, that is, relatively ion-rich centers and ion-poor outskirts, was proposed. PBSIs with K ions were found to show higher crystallization temperatures than those with Na ions in the non-isothermal crystallization from the melts. These results indicate that the crystallization behavior of PBSIs is dominated by the ionic aggregates which induce the crystal nucleation around themselves.

A series of P(3HB-co-3MP)s with different 3MP unit content was biosynthesized by the fermentation of W. eutropha in a medium containing sodium gluconate and DTDP as carbon sources at different pH conditions ranging from pH 6.0 to 8.0. The P(3HB-co-3MP) samples were fractioned using the solvent/nonsolvent mixed solvent chloroform/heptane and the comonomer unit composition was investigated. It was found that W. eutropha produces P(3HB-co-3MP)s with extremely different 3MP unit content ranging from 3.6 to 70.0 mol-%, depending on the pH value of the fermentation medium. The copolyester samples produced in mild basic medium have a considerably narrower compositional distribution than the samples from acidic medium. The highest polymer yield was obtained at pH 8.0.DSC diagram for P(3HB-co-3MP)s biosynthesized in different pH medium. [graph: see text] DSC diagram for P(3HB-co-3MP)s biosynthesized in different pH medium.

Poly(butylene succinate) (PBS) and PBS-based ionomers (PBSi's) with 0.3 and 1.2 mol-% of sodium sulfonated succinate unit were synthesized. The existence of ionic aggregates in the ionomer matrices was indicated by melt viscosity and glass transition data. It seems that the ionic aggregates have two opposing roles in crystallization: one is the induction of nucleation and the other is the interference with lamellar growth. Because of these two contrary effects, the crystallization behavior of the ionomers exhibited measurably different cooling rate-dependencies than that of the parent PBS. The rate varied distinctly with ionic content.

A series of poly(3-hydroxybutyrate-co-4-hydroxybutyrate)s [P(3HB-co-4HB)s] with different 4HB content, biosynthesized by Ralstonia eutropha H16 with mixed carbon sources of 4-hydroxybutyric acid (4HBA) and butyric acid, were fractionated by solvent/nonsolvent fractionation into copolyester fractions with different 4HB content and narrower compositional distribution. The fractions obtained were classified into two groups, 3HB- and 4HB-rich P(3HB-co-4HB)s. The thermal properties were investigated for these fractionated copolyesters. With increasing 4HB content, the melting temperature at first decreased while 3HB content was rich, and then increased while 4HB content was rich. The glass transition temperature decreased linearly with increasing 4HB content. The 4HB-rich P(3HB-co-4HB) was found to be immiscible with the 3HB-rich P(3HB-co-4HB), as two glass transitions corresponding to those of respective P(3HB-co-4HB)s were observed by DSC. It was concluded that as-produced bacterial P(3HB-co-4HB) samples used in this study should be considered as immiscible polymer blends.

The specific intermolecular hydrogen-bonding interaction between some poly(hydroxyalkanoic acid)s (PHAs) and 4,4’-thiodiphenol (TDP) were studied by DSC and FT-IR. Chemosynthetic poly(3-hydroxypropionate), bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and bacterial poly(3-hydroxybutyrate- co-4-hydroxybutyrate) were used as the PHA samples. A curve-fitting program for line-shape analysis of FT-IR spectra was also applied to investigate the fractions of associated carbonyl groups. The measurements show there are strong intermolecular hydrogen bonds between the carbonyl groups of PHAs and the hydroxyl groups of TDP. The content of intermolecular hydrogen bonds is influenced by both the content of TDP in the PHA/TDP blends and the crystallizability of PHAs. The crystallizability is related to the flexibility of the molecular chains. With the addition of TDP to PHAs, the decrease of melting point Tm and the increase of glass transition temperature Tg of the component of PHAs in the blends were found. When the content of TDP was more than 40%, phase separation took place, which was so serious that Tg dropped obviously as soon as the content of TDP was up to 80%. At this time, it is difficult for the molecules of PHAs and TDP to form intermolecular hydrogen bonds. As indicated by the study of FT-IR, TDP has more ability to form the self-hydrogen-bond of TDP-HO···HO-TDP type than the inter-hydrogen-bond of PHA-C=O···HO-TDP type. Based on the analysis on the eutectic behavior in different PHA/TDP pairs, it was found that the bulkiness of the pendant alkyl groups in the chains of PHAs affects the eutectic behavior.

A novel cyclic trimer of imidazole 1, in which imidazole rings are connected by amide bonds, has been synthesized with the help of LiCl as a template for the cyclization. The absorption spectra of 1 indicate the extension of conjugation between imidazole rings and amide bonds. The addition of 3 M equiv of MgCl2 solubilizes 1 in polar organic solvent, suggesting the chelating ability of 1 to Mg cation.

Readily recyclable biobased plastics were designed and synthesized utilizing the thermally reversible DA reaction. Furyl-telechelic poly(butylene succinate) prepolymers (PBSF(2)) were extended with bis- and tris-maleimide linkers (M(2) and M(3)) by the DA reaction in the bulk state to produce linear and network polymers, respectively. The DA reaction was able to proceed at 25-80 degrees C, at which crystalline domains of PBSF(2) were present. In the linear polymer system, the molecular weight in the reaction equilibrium was dependent on the chain length of the prepolymer, but almost independent of the reaction temperature. The cycle of DA and retro-DA reactions was repeatable with no prepolymer deterioration.