Solution-cast Thin Films Research Articles

Structural characterization of nylon 7 by solid-state nuclear magnetic resonance, differential scanning calorimetry and attenuated total reflectance Fourier transform infra-red spectroscopy

Samples of commercial nylon 7 were given different thermal or precipitation histories. Structure and crystallinity were followed by d.s.c., solid-state n.m.r. and attenuated total reflectance Fourier transform infra-red spectroscopy (ATR FTi.r.). Heat of fusion and melting temperature values ranged from 52 to 93 J g −1 and 228 to 242°C, respectively. Surprisingly, annealing did not give material with the greatest heat of fusion although it possessed the highest melting point. Solid-state 13C and 15N n.m.r. methods were used to observe the amorphous and crystalline fractions. For example, the amide nitrogens show resonances near 86.5 ppm in amorphous domains, near 84 ppm in α-crystals and near 89 ppm in γ-crystals. 15N cross-polarization/magic angle spinning spectra of solution cast samples contained peaks consistent with all three domains in various intensity ratios but with the γ-peak being the most intense for most samples. Solid-state 13C spectra contained peaks which supported the presence of these phases but with the α-phase peaks predominating. Treatment of solution-cast thin films with aqueous KI I 2 gave materials whose n.m.r. spectra contained peaks consistent with these three phases in different ratios than for the initial solution-cast samples. Spectra of the melt crystallized samples contained peaks for amorphous and α-domains only. 13C spin-lattice relaxation ( T 1) magnetization decays could be fit to two or three exponentials ( T 1s of hundreds of milliseconds, a few seconds and hundreds of seconds) consistent with semicrystalline polymer behaviour. T 1 values for the long-relaxing component ranged from 350 to 23 s for the annealed and precipitated samples, respectively. Amide V bands near 682 cm −1, assigned previously to the α-phase, were present in the ATR FTi.r. spectra of all the samples. However, the chemically treated and solution cast samples contained additional bands at 690 and 620 cm −1 due to the γ-phase. Spectra of quenched samples contained bands not seen in the other spectra.

Morphology of solution-cast thin films of wholly aromatic thermoplastic polyimides with various molecular weights

The morphology of solution-cast thin films of wholly aromatic thermoplastic polyimides (TPIs) with various molecular weights ( M w =3490-85 800) was studied using transmission electron microscopy (TEM). Thin TPI films suitable for TEM studies were prepared from 0.3% solution in p -chlorophenol/phenol cast onto hot polyphosphoric acid, where the solvent was evaporated. A TPI oligomer of M w =3490-6500 forms droplet-like structure (D structure) during casting, whereas TPIs with higher molecular weights ( M w =23 900-85 800) form ellipsoidal and elongated structures. On heating the as-cast film of TPI with M w =3490, the D structure is converted into a flat, layer structure with extended chains, which gives an electron diffraction pattern of the single-crystal type. On the other hand, long curved crystals with folded chains develop in the D structure of a TPI with molecular weight of 6500. The supermolecular structures of TPIs with higher molecular weights ( M w =23 900-85 800) are noticeably affected by the molecular orientation in the original structure of the as-cast films. Oriented crystallization occurs in the elongated structure, while lamellar crystals develop in the D structure or ellipsoidal structures.

Picosecond transient Raman scattering in polydiacetylene 4-BCMU films

Picosecond transient resonant Raman scattering (TPRRS) measurements at room temperature have been completed on solution-cast thin films of polydiacetylene 4-BCMU. We observed a transient reduction of a few percent in Raman scattering intensity for both C = C and C = C stretching vibrations when pumping at the absorption edge; this is explained by saturation of the RRS cross section caused by photogenerated excitons. At low pump intensities (<5 MW/cm 2) the TPRRS decay is quite fast (of order 3 ps) and the TPRRS spectra follow the regular Raman lineshape. For high pump intensities (>15 MW/cm 2), however, a narrow spectral hole burning in TPRRS is observed and the TPRRS decay becomes considerably longer. The latter effect is explained by a phonon-mediated stark effect which is enhanced under resonance conditions.

Squaraine chemistry. Synthesis and characterization of squaraine dyes having self-organizing properties

A series of mono-substituted N-alkylsquaraines of chain length varying from 2 carbons to 18 carbons have been synthesized by condensing 1-p-dimethylaminophenyl-2-hydroxycyclobutene-3,4-dione with N-methyl-N-alkylanilines. All the N-alkylsquaraines synthesized were soluble in chlorinated solvents and were purified by a solvent extraction technique. Their spectroscopic properties (IR, VIS, 1H NMR and MS) were found to be typical of squaraines. Examinations of the solid-state properties of these materials, by solid-state absorption spectroscopy and by X-ray powder diffraction technique, indicate that the molecules of N-alkylsquaraines form microcrystalline aggregates, analogous to those observed in their photoconductive pigmentary analogs, in the solid state. This observation is in contrast to that seen in other soluble squaraines, where the aggregation is usually perturbed by solubilizing groups. This unique aggregational behavior leads us to propose that there exists a dual intermolecular interaction in the microcrystalline state of N-alkylsquaraines. In addition to the expected intermolecular donor-acceptor interaction between the squaraine chromophores, a hydrophobic interaction between N-alkyl groups occurs. The N-alkyl groups in these materials not only solubilize the squaraine but also provide a proper orientation for the aggregation process. This model suggests that N-alkylsquaraines should have the ability to self-organize and form photoconductive aggregates under various processing conditions. This ability has been verified in the case of solution cast thin films by absorption spectroscopy.

The structure of γ-polypivalolactone: a combined analysis of single-crystal electron diffraction data and powder X-ray diffraction profiles with the Rietveld method

The crystal structure of the γ-phase of polypivalolactone (γ-PPVL) has been determined from electron diffraction data and tested with the Rietveld method against X-ray powder diffraction profiles. The electron diffraction study is based on single-crystal patterns obtained from melt-crystallized solution-cast thin films, while the Rietveld analysis was performed on data from melt-crystallized samples containing comparable amounts of α- and γ-phase PPVL. The crystal class is orthorhombic (space group P2 12 12 1), and two molecules with the same chirality and opposite directions pass through the unit cell having lattice dimensions a = 8.23, b = 11.28, c( chain repeat) = 6.02 A ̊ . Both h k 0 and tilted-specimen electron diffraction data were used in the refinement, carried out in the kinematic approximation. The analysis based on these data and on powder profiles coherently indicates that the refined structural model has a main-chain conformation intermediate between the one found in the α-phase and the minimum-energy conformation, while differing significantly from both.

Organic Photovoltaic Materials: Squarylium and Cyanine-TCNQ Dyes

The photovoltaic properties of Schottky barrier sandwich cells consisting of sublimed and solution-cast thin films of selected squarylium (bis-anilino derivatives of cyclobuta-1,3-diene-2,4-dione) and cyanine-tetracyanoquinodimethanide (TCNQ) dyes have been measured. For hydroxy squarylium (OHSq), maximum power conversion efficiencies (η) were 0.2% for 850-nm light (1 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ); 0.05% for 633-nm light (94 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ); 0.06% for “white” light (21 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ); 0.15% for low intensity (0.14 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) simulated AM0 light (sunlight under outer space conditions), and 0.02% for high intensity (140 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) AM0 light. Efficiencies of selected OHSq cells were observed to increase fivefold when the cells were doped with bromine or 1-phenyl-3-p-N, N-diethylaminostyryl-5-p-N,N-diethylaminophenyl-Δ <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -pyrazoline (DEASP), e.g., 0.05 to 0.23% (Br); 0.004 to 0.021% (DEASP). The efficiency of a solution-cast cell of amorphous 2,2′-dicarbocyanine-TCNQ was 0.02% when 933-nm light (approximately (1 mW/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) was used. Amorphous solid solutions of 1,1′-diethyl-2,2′-dicarbocyanine-and oxa-2,2′-dicarbocyanine-TCNQ salts were also tested. The effects of various material and device properties on the performance of organic photovoltaic cells are discussed, and it is proposed that organic solar cells having efficiencies of one percent or more can be made by using existing technologies.

Surface morphology of siloxane block copolymer crystals: (Tetramethyl-p-silphenylenejsiloxane—dimethylsiloxane

Abstract The metal decoration technique was applied to solution grown crystals and cast thin films of (tetramethyl-p-silphenylene) siloxane and dimethylsiloxane (DMS) block copolymers in order to elucidate their surface textures as a function of copolymer composition. Electron diffraction and microscopy studies were used. Metal-free zones are observed at surface steps of single crystals, and decorating particles occasionally form spiral growths in the inner regions of crystals. However, the decorating particles form regular patterns, particularly on the copolymer crystal surfaces. In the case of solution-cast thin films, deposition of metallic particles occurs along lamellar crystal edges or where a fibrillar morphology occurs. The nucleation density of metallic particles depends on the copolymer composition and increases with increasing crystallinity of the samples. Probable models are suggested to account for this surface texture. The propensity for screw-dislocations crystal growths on the crystal surfaces decreases as the noncrystallizable DMS component increases.