Solid-state Morphology Research Articles

Living anionic polymerization of 4‐diphenylphosphino styrene for ABC triblock copolymers

Living anionic polymerization of 4-diphenylphosphino styrene (DPPS) achieved unprecedented poly(S-b-I-b-DPPS) ABC triblock copolymers with predictable molecular weights and narrow polydispersities. In situ Fourier transform infrared spectroscopy probed the anionic polymerization, monitoring vinyl disappearance during sequential monomer addition for kinetic analysis. Varying the concentration of reinforcing, polystyrenic external blocks enabled diverse compositions with tunable thermomechanical properties and tailored morphology. Dynamic mechanical analysis confirmed the presence of microphase separation in the triblock copolymers and revealed a broad temperature range (ca 100 oC) for a plateau region and onset of flow temperatures above 100 oC. Small-angle X-ray scattering and atomic force microscopy collectively revealed solid state morphologies of the triblock copolymers and probed phase separation at the nanoscale. Well-defined poly(S-b-I-b-DPPS) ABC triblock copolymers with tunable structure − property relationships now permit phosphorus-containing thermoplastic elastomers for emerging applications. © 2016 Society of Chemical Industry

Structural and spectroscopic studies of 2,9-dimethyl-1,10-phenanthrolinium cation (DPH) with chloride, triflate and gold dicyanide anions. The role of H-bonding in Molecular recognition and enhancement of - stacking

The crystal structures of the pronated ligand, 2,9-dimethyl-1,10-phenanthrolinium (DPH) cation with selected counter anions (chloride (1), triflate (2), and gold dicyanide (3)) are reported. The role of a hydrogen bond interaction in influencing the solid state p-p stacking found in all three compounds has been investigated. In the chloride, and triflate adducts 1 and 2, respectively, the solid state morphology was stabilized by additional H-bonding interaction. In particular, compound 1 displays extensive network of H-bonding interaction where p-p stacked layers are interlinked through the H-bonding network. In compound 2, the H-bonding interaction is less pronounced and involves mainly the non-coordinating triflate anion and the protonated N atom of the cation connecting neighboring intra-layer molecules. In 3 a weaker interaction exists between the N atom of the Au(CN)2- anion and the protonated N of the ligand, but the system lacks extensive intra- or inter-layer H-bonding interaction that connects the neighboring molecules. KEY WORDS: Phenanthroline, H-bonding, X-ray structure, p- p stacking Bull. Chem. Soc. Ethiop. 2016, 30(2), 231-239.DOI: http://dx.doi.org/10.4314/bcse.v30i2.7

Cofacial Versus Coplanar Arrangement in Centrosymmetric Packing Dimers of Dipolar Small Molecules: Structural Effects on the Crystallization Behaviors and Optoelectronic Characteristics.

Two D-π-A-A molecules (MIDTP and TIDTP) composed of an electron-rich ditolylamino group (D) and an electron-deficient 5-dicyanovinylenylpyrimidine (A-A) fragment bridged together with indeno[1,2-b]thiophene (IDT) were synthesized. These molecules provide an opportunity to examine in-depth the impact of side-chain variations (methyl vs p-tolyl) on the crystallization behaviors, solid-state morphology, physical properties, and optoelectronic characteristics relevant for practical applications. X-ray analyses on single-crystal structures indicate that methyl-substituted MIDTP forms "coplanar antiparallel dimers" via C-H···S interactions and organizes into an ordered slip-staircase arrays. In contrast, p-tolyl-bearing TIDTP shows "cofacial centrosymmetric dimers" via π-π interactions and packs into a less-ordered layered structures. The X-ray diffraction analyses upon thermal treatment are consistent with a superior crystallinity of MIDTP, as compared to that of TIDTP. This difference indicates a greater propensity to organization by introduction of the smaller methyl group versus the bulkier p-tolyl group. The increased propensity for order by MIDTP facilitates the crystallization of MIDTP in both solution-processed and vacuum-deposited thin films. MIDTP forms solution-processed single-crystal arrays that deliver OFET hole mobility of 6.56 × 10(-4) cm(2) V(-1) s(-1), whereas TIDTP only forms amorhpous films that gave lower hole mobility of 1.34 × 10(-5) cm(2) V(-1) s(-1). MIDTP and TIDTP were utilized to serve as donors together with C70 as acceptor in the fabrication of small-molecule organic solar cells (SMOSCs) with planar heterojunction (PHJ) or planar-mixed heterojunction (PMHJ) device architectures. OPV devices based on higher crystalline MIDTP delivered power conversion efficiencies (PCEs) of 2.5% and 4.3% for PHJ and PMHJ device, respectively, which are higher than those of TIDTP-based cells. The improved PCEs of MIDTP-based devices are attributed to better hole-transport character.

A structure-property study toward π-extended phosphole chromophores with ambipolar redox properties

We report the synthesis of a series of π-extended dithienophospholes with phenyl or biphenyl terminal groups via Suzuki Miyaura cross-coupling procedures. The incorporation of the dithienophosphole core into the scaffold on oligophenylenes was found to lead to pronounced luminescence properties in solution and the solid state, the latter of which also responded to different solid-state morphologies, i.e., powder versus crystal. More importantly, the investigated molecular architectures also allowed — for the first time — the observation of ambipolar redox behavior of such species, with the biphenyl-extended species in particular showing quasi-reversible reduction and oxidation processes; the observed experimental features were correlated with computational density functional theory studies.

The effect of thermal annealing in a hydrogen atmosphere on tungsten deposited on 6H[sbnd]SiC

Tungsten (W) film was deposited on a bulk single crystalline 6HSiC substrate and annealed in H2 ambient at temperatures of 700 °C, 800 °C and 1000 °C for 1 h. The resulting solid-state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectrometry (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM) analysis techniques. These results are compared with the vacuum annealed results reported in our earlier work. As-deposited RBS results indicated the presence of W and O2 in the deposited thin film, the GIXRD showed the presence of W, WO3, W5Si3 and WC. RBS results indicated the interaction between W and SiC was accompanied by the removal of oxygen at 700 °C. The GIXRD analysis indicated the presence of W5Si3 and WC in the samples annealed at 700 °C. At temperatures of 800 °C and 1000 °C, W annealed in a H2 ambient further reacted with the SiC substrate and formed a mixed layer containing silicide phases and carbide phases, i.e.W5Si3, WSi2, WC and W2C. The SEM micrographs of the as-deposited samples indicated the W thin film had a uniform surface with small grains. Annealing at 800 °C led to the agglomeration of W grains into clusters making the surface rough.

Chain Architecture as an Orthogonal Parameter To Influence Block Copolymer Morphology. Synthesis and Characterization of Hyperbranched Block Copolymers: HyperBlocks

For block copolymers there is usually a strong correlation between the copolymer composition (volume fraction of each block) and the resulting solid state morphology. However, for a variety of potential applications, e.g., semipermeable membranes or templates, it might be desirable to vary the microphase morphology independently of copolymer composition. The use of chain branching is an additional and orthogonal parameter to influence morphology, independently of composition, and we explore for the first time the impact of a long-chain, hyperbranched architecture on the microphase-separated, solid state morphology of branched block copolymers. To this end, a series of functionalized linear ABA (polystyrene–polyisoprene–polystyrene) triblock copolymers (macromonomers), hyperbranched ABA triblock copolymers (HyperBlocks), and blends of HyperBlocks with a commercially available linear ABA triblock copolymeric thermoplastic elastomer were prepared. Moreover, the “macromonomer” approach is the only feasible route to prepare hyperbranched block copolymers. The solid state morphology of the resulting materials was investigated by a combination of transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) which showed a dramatic impact of the chain architecture on the resulting morphology. While the linear ABA triblock copolymers showed the expected microphase-separated morphology with long-range order dependent upon composition, no long-range order was observed in the HyperBlocks. Instead, the HyperBlocks revealed a microphase-separated morphology without long-range lattice order, irrespective of macromonomer composition or molecular weight. Furthermore, when HyperBlocks were subsequently blended with a commercially available linear ABA triblock copolymer (Kraton D1160), the HyperBlock appeared to impose a microphase-separated morphology without long-range lattice order upon the linear copolymer even when the HyperBlock is present as the minor component in the blend at levels as low as 10 wt %.

Interfacial reactions and surface analysis of W thin film on 6H-SiC

Tungsten (W) thin film was deposited on bulk single crystalline 6H-SiC substrate and annealed in vacuum at temperatures ranging from 700 to 1000°C for 1h. The resulting solid-state reactions, phase composition and surface morphology were investigated by Rutherford backscattering spectroscopy (RBS), grazing incidence X-ray diffraction (GIXRD) and scanning electron microscopy (SEM). XRD was used to identify the phases present and to confirm the RBS results. The RBS spectra were simulated using the RUMP software in order to obtain the deposited layer thickness, composition of reaction zone and detect phase formation at the interface. RBS results showed that interaction between W and SiC started at 850°C. The XRD analysis showed that WC and CW3 were the initial phases formed at 700 and 800°C. The concentration of the phases was however, too low to be detected by RBS analysis. At temperatures of 900 and 1000°C, W reacted with the SiC substrate and formed a mixed layer containing a silicide phase (WSi2) and a carbide phase (W2C). The SEM images of the as-deposited samples showed that the W thin film had a uniform surface with small grains. The W layer became heterogeneous during annealing at higher temperatures as the W granules agglomerated into island clusters at temperatures of 800°C and higher.

New semi-conducting poly(phenylene vinylene-alt-anthrylene vinylene)s: Synthesis, characterization and photophysical properties

An anthracene-based semi-conducting polymer (P1) and its cyano-analogue (P2) were synthesized via the Wittig and Knoevenagel polycondensations. The polymers were soluble in common organic solvents and have number-average molecular weights of 13,750 and 6430gmol−1 for P1 and P2, respectively. The DSC analyzes show a good thermal stability and an amorphous morphology in solid state for these organic materials. The optical properties of the polymers were investigated by UV–visible absorption and fluorescence spectroscopies. The HOMO and LUMO levels were estimated using cyclic voltammetry analysis. The effect of cyano group on the photophysical properties of poly(phenylene vinylene-alt-anthrylene vinylene)s was investigated. The results demonstrate an enhancement in the ionization potential and a significant improvement of the fluorescence yield due to introduction of such groups into the π-conjugated system. Single-layer diodes based on these organic semiconductors have been fabricated and showed relatively low turn-on voltages.

Effect of chain stiffness on the competition between crystallization and glass-formation in model unentangled polymers.

We map out the solid-state morphologies formed by model soft-pearl-necklace polymers as a function of chain stiffness, spanning the range from fully flexible to rodlike chains. The ratio of Kuhn length to bead diameter (lK/r0) increases monotonically with increasing bending stiffness kb and yields a one-parameter model that relates chain shape to bulk morphology. In the flexible limit, monomers occupy the sites of close-packed crystallites while chains retain random-walk-like order. In the rodlike limit, nematic chain ordering typical of lamellar precursors coexists with close-packing. At intermediate values of bending stiffness, the competition between random-walk-like and nematic chain ordering produces glass-formation; the range of kb over which this occurs increases with the thermal cooling rate |Ṫ| implemented in our molecular dynamics simulations. Finally, values of kb between the glass-forming and rodlike ranges produce complex ordered phases such as close-packed spirals. Our results should provide a useful initial step in a coarse-grained modeling approach to systematically determining the effect of chain stiffness on the crystallization-vs-glass-formation competition in both synthetic and colloidal polymers.

Correlation between positron annihilation lifetime parameters and T1ρ relaxation times determined from solid state NMR at the compositional phase segregation point of graft copolymers

A series of poly(methyl methacrylate)-graft-polystyrene copolymers were prepared using the macromonomer “grafting through” technique. The branch density was varied by variation of the feed ratios in the free radical copolymerization. The macromonomer branch length was controlled by using the living anionic polymerization technique. The graft copolymers were characterised by solution 1H NMR and SEC-MALLS to determine the composition of the graft copolymers. Positron annihilation lifetime spectroscopy (PALS), and solid state NMR (SS-NMR) were used to investigate the solid state morphology of the graft copolymers. The ortho-positronium lifetime (τ3) and the T1ρ relaxation times from solid state NMR analysis was used to determine the compositional phase segregation point in the copolymer series. The result shows that the information from these two techniques is complimentary and provides useful information to explain the variation in the Tg and positron lifetime parameters as a function of composition.

De Novo Design of a New Class of "Hard-Soft" Amorphous, Microphase-Separated, Polyolefin Block Copolymer Thermoplastic Elastomers.

Sequential cyclic/linear/cyclic living coordination polymerization of 1,6-heptadiene (HPD), propene, and HPD, respectively, employing the well-defined and soluble group 4 transition-metal initiator, {(η5-C5Me5)Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)4], provides the stereoirregular, amorphous poly(1,3-methylenecyclohexane)-b-atactic polypropene-b-poly(1,3-methylenecyclohexane) (PMCH-b-aPP-b-PMCH) polyolefin triblock copolymer (I) in excellent yield. By varying the weight fraction of the end group, minor component "hard" PMCH block domains, fPMCH, relative to that of the midblock "soft" aPP domain, three different compositional grades of these polyolefin block copolymers, Ia-c, were prepared and shown by AFM and TEM to adopt microphase-separated morphologies in the solid state, with spherical and cylindrical morphologies being observed for fPMCH = 0.09 (Ia) and 0.23 (Ic), respectively, and a third more complex morphology being observed for Ib (fPMCH = 0.17). Tensile testing of Ia-c served to establish these materials as a new structural class of polyolefin thermoplastic elastomers, with Ia being associated with superior elastic recovery (94 ± 1%) after each of several stress-strain cycles.

Poly((2-alkylbenzo[1,2,3]triazole-4,7-diyl)vinylene)s for organic solar cells

Poly((2-Alkylbenzo[1,2,3]triazole-4,7-diyl)vinylene)s (pBTzVs) synthesized by Stille coupling show different absorption spectra, solid-state morphology, and photovoltaic performance, depending on straight-chain versus branched-chain (pBTzV12 and pBTzV20) pendant substitution. Periodic boundary condition density functional computations show limited alkyl pendant effects on isolated chain electronic properties; however, pendants could influence polymer backbone conjugative planarity and polymer solid film packing. The polymers are electronically ambipolar, with best performance by pBTzV12 with hole and electron transport mobilities of 4.86 × 10−6 and 1.96 × 10−6 cm2 V−1 s−1, respectively. pBTzV12 gives a smooth film morphology, whereas pBTzV20 gives a very different fibrillar morphology. For ITO/PEDOT:PSS/(1:1 w/w polymer:PC71BM)/LiF/Al devices, pBTzV12 gives power conversion efficiency (PCE) up to 2.87%, and pBTzV20 gives up to PCE = 1.40%; both have open-circuit voltages of VOC = 0.6–0.7 V. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1539–1545

Effect of electron-donating unit on crystallinity and charge transport in organic field-effect transistors with thienoisoindigo-based small molecules

We report the effect of an electron-donating unit on solid-state crystal orientation and charge transport in organic field-effect transistors (OFETs) with thienoisoindigo (TIIG)-based small molecules. End-capping of different electron-donor moieties [benzene (Bz), naphthalene (Np), and benzofuran (Bf)] onto TIIG (giving TIIG-Bz, TIIG-Np, and TIIG-Bf) is resulted in different electronic energy levels, solid-state morphologies and performance in OFETs. The 80°C post-annealed TIIG-Np OFETs show the best device performance with a best hole mobility of 0.019cm2V−1s−1 and threshold voltage of −8.6±0.9V using top gate/bottom contact geometry and a CYTOP gate dielectric. We further investigated the morphological microstructure of the TIIG-based small molecules by using grazing incidence wide angle X-ray scattering, atomic force microscopy and a polarized optical microscope. The electronic transport levels of the TIIG-based small molecules in thin-film states were investigated using ultraviolet photoelectron spectroscopy to examine the charge injection properties of the gold electrode.

Microphase Separation and Crystallization in H-Bonding End-Functionalized Polyethylenes

Well-defined, crystalline, low molar mass polyethylene PEx (where x is the molar mass 1300 and 2200 g mol–1) bearing thymine (Thy) or 2,6-diaminotriazine (DAT) end groups have been synthesized from amino-terminated PE. Either double-layer or monolayer solid-state morphologies were attained depending on the nature of the end-group(s). PE1300-NH2, PE1300-DAT, and the equimolar blend PE1300-Thy/DAT-PE1300 all organized into double-layer structures composed of extended PE chains sandwiched between H-bonding chain-ends. The double-layered morphology arose from the microphase separation of the polar end-groups and the nonpolar PE chains and was frozen by the crystallization of the PE domains. The regularity of the PE lamellar stacking was higher for the stronger and more directional associated pair Thy/DAT compared with samples of either PE-NH2 or PE-DAT. For PE1300-Thy, the mesoscopic organization was driven by the crystallization of Thy domains prior to crystallization of the PE chains, forcing the small prop...

Supercritical CO2 antisolvent precipitation from biocompatible polymer solutions: A novel sustainable approach for biomaterials design and fabrication

Supercritical CO2 (scCO2) is used as an antisolvent to assist the precipitation of poly(ɛ-caprolactone) (PCL) and poly(ethylene oxide) (PEO) from biocompatible solvents such as ethyl lactate (EL) and ethyl acetate (EA). Compared to precipitation by standard air-drying methods, through which a limited number of polymer structures can be achieved, the use of scCO2 offers the opportunity to tune the solid-state morphology of the material, which may assume the form of continuous films, discrete precipitates and/or porous microparticles, possibly passing from one to other by adjusting the temperature, pressure and solution composition. The crystalline structure and surface texture of the samples are assessed by means of optical, electron and confocal microscopy. Under certain conditions, scCO2 is found to plasticize the polymer, promoting partial or complete recrystallization phenomena and eventually giving rise to bimodal spherulite size distributions.

Characterization of recrystallized itraconazole prepared by cooling and anti-solvent crystallization

The objective of the present study was to alter the crystal habit of itraconazole (ITZ) by cooling and anti-solvent crystallization and characterize its properties. ITZ was recrystallized in different solvents and the effects of each solvent on morphology of crystals, dissolution behavior and solid state of recrystallized drug particles were investigated. The results revealed that ITZ crystals recrystallized by cooling and anti-solvent crystallization showed the different crystal habits from the untreated ITZ. Using cooling crystallization tended to provide needle-shaped crystals while the crystals obtained from anti-solvent crystallization showed more flaky, plate shape. This indicated the importance of preparation method on nucleation and crystal growth. No change in drug polymorphism was observed, according to determination of thermal property and crystalline state by differential scanning calorimetry and powder X-ray diffractometry, respectively. The recrystallized ITZ showed higher drug dissolution than untreated ITZ and the highest drug dissolution was observed from the samples recrystallized in the presence of PEG 200, which provided the small plate-shaped crystals with tremendously increased in surface area. However, the increasing of drug dissolution is relatively small, therefore, further development may be required.

Visualizing order in dispersions and solid state morphology with Cryo-TEM and electron tomography: P3HT : PCBM organic solar cells

Building blocks for organic solar cells are made from P3HT in a P3HT : PCBM solution in toluene and used to tune the morphology of the photoactive layer.

Multi-phase microstructures drive exciton dissociation in neat semicrystalline polymeric semiconductors

The exciton dissociation yield of macromolecular semiconductors depend fundamentally on their solid-state microstructure and phase morphology.

An electron-deficient small molecule accessible from sustainable synthesis and building blocks for use as a fullerene alternative in organic photovoltaics.

An electron-deficient small molecule accessible from sustainable isoindigo and phthalimide building blocks was synthesized via optimized synthetic procedures that incorporate microwave-assisted synthesis and a heterogeneous catalyst for Suzuki coupling, and direct heteroarylation carbon-carbon bond forming reactions. The material was designed as a non-fullerene acceptor with the help of DFT calculations and characterized by optical, electronic, and thermal analysis. Further investigation of the material revealed a differing solid-state morphology with the use of three well-known processing conditions: thermal annealing, solvent vapor annealing and small volume fractions of 1,8-diiodooctane (DIO) additive. These unique morphologies persist in the active layer blends and have demonstrated a distinct influence on device performance. Organic photovoltaic-bulk heterojunction (OPV-BHJ) devices show an inherently high open circuit voltage (Voc ) with the best power conversion efficiency (PCE) cells reaching 1.0 V with 0.4 v/v % DIO as a processing additive.

Solar Cells: Understanding the Charge‐Transfer State and Singlet Exciton Emission from Solution‐Processed Small‐Molecule Organic Solar Cells (Adv. Mater. 43/2014)

World-record-performing bulk-heterojunction (BHJ) small molecule solar cells are realized by careful optimization of their solid-state morphology. These BHJ films are transformed from an intimate mixture of the donor and acceptor phases to films with well-defined donor crystallites. In addition to correlating with a high photovoltaic response, the donor crystallites also appear to be linked with the emergence of donor singlet electroluminescence at low applied biases, where only charge-transfer-state emission is expected. On page 7405, T.-Q. Nguyen and co-workers study three blends of high-performing small-molecule solar-cell systems that show the same trend of emerging singlet emission upon an optimized photovoltaic response.