Film morphology and molecular orientation in oligothiophene-fluorene films

The effects of processing conditions on film morphology and molecular orientation were studied for a novel conjugated fluorene-bithiophene oligomer, oligo(9,9-dioctylfluorene-alt-bithiophene) (OF8T2). Depending on the method of film preparation, OF8T2 molecules adopt different orientations in the films. X-ray diffraction peak at 4.9° of the OF8T2 film deposited from petroleum ether/dichloromethane mixture is attributed to a layering distance between sheets of OF8T2 chains, which are separated by the octyl side chains. Preferred orientation is clearly inferred through the absence of peaks corresponding to π-π stacking. For the spin-coated film after annealing, X-ray diffraction patterns indicate the presence of lamellar structure with the plane of the conjugated backbone normal to the substrate. The molecules were aligned with long axes along the rubbing direction when the spin-coated film was rubbed and then annealed. These results suggest a convenient approach for preparing active layers for organic optoelectronic devices by simple solution methods.     

Surface morphology and crystalline orientation of uniaxially drawn polytetrafluoroethylene films

For polytetrafluoroethylene (PTFE) films drawn uniaxially at 100, 150, 250, and 350°C, the morphology and degree of crystalline orientation were investigated by electron scanning microscopy and wide-angle X-ray diffraction, respectively. On the surface of the PTFE films which were heat-treated at 350°C for 2 h before the drawing, granules with a diameter of about 2 μm and bands with a width of about 0.3 μm were observed. By the drawing below the melting point, the bands are transformed into fibrils and a porous structure is formed by the drawing above the draw ratio (λ) of about 1.3. By drawing above the melting point, striations appear perpendicularly to the draw direction, and the collapse of the granules is observed. The orientation of the crystallites increases rapidly with increasing the draw ratio and approaches a plateau at λ ≈ 1.5 for the films drawn above the melting point and at λ ≈ 2.0 for that below it.     

Phenomenological and mathematical analysis of the orientation in biaxially drawn polymeric films

Equations are derived that relate the orientation of “pseudo-affine” reoriented structural units after a biaxial deformation to the degrees and the directions of the effective drawings. The connection between these drawing parameters and those externally applied is analyzed in detail. It is shown how a comparison of these two sets of drawing parameters allows conclusions regarding the distribution throughout the material of the stresses that cause the deformation, the inhomogeneity of the deformation, and the role of non-orienting flow during deformation. In particular, the orientation of biaxially drawn poly(ethylene terephthalate) films is investigated, and it is shown what general information can be obtained on the deformation behavior of this material on the basis of these considerations.     

Preparation and properties of hollow BN fibers derived from polymeric precursors

Boron nitride (BN) complex precursors were synthesized from a mixture of 2,4,6-tri(methylamino)borazine ([CH₃(H)N]₃B₃N₃H₃) and tris(methylamino)borane ([B(NHCH₃)₃]). The reactions between the two mixtures aimed at producing polymeric green fibers via a melt-spinning process and producing novel hollow BN ceramic fibers with various shell thicknesses by curing and pyrolysis. The properties and pyrolytic process of the complex precursors were characterized by TG-DSC-FTIR-MS online coupling analysis. The microstructure, solid phase, and morphologies of hollow BN fibers were investigated using XRD, SEM, TEM, and elementary analysis. Results showed that the synthesized fibers were highly pure and uniform with a mean diameter of 9 μm. The dielectric properties of the BN fibers were excellent with a dielectric constant of 2.90 and a dielectric loss factor of 0.00064. These results confirm that the ceramic fibers synthesized using the novel complex polymeric precursors indicate their adequate properties as micro-wave transparence reinforcements.     

Microstructure and grain size dependence of ferroelectric properties of BaTiO3 thin films on LaNiO3 buffered Si

BaTiO₃ films were prepared by radio frequency sputtering on the LaNiO₃/Si substrates and then annealed at different temperatures. The films exhibit a highly (1 0 0)-oriented structure and their grain size range from 14 to 55 nm after annealing. Polarization-reversal characteristics for different BaTiO₃ films were measured. The results show that while obvious ferroelectricity is obtained for films with grain size larger than 22 nm, a weak ferroelectricity is still observed in BaTiO₃ film of 14 nm grains, indicating that if a critical grain size exists for ferroelectricity it is less than 14 nm for polycrystalline BaTiO₃ on LaNiO₃/Si. The suppression of macroscopic ferroelectricity for BaTiO₃ with finest grain size and the grain size dependence of remnant polarization and coercive field are also discussed in detail.     

Tailoring the morphology of WO3 films with substitutional cation doping: Effect on the photoelectrochemical properties

With the aim of improving the performance and extending the range of applications of mesoporous WO₃ films, which were initially developed for the photoelectrochemical oxidation of water, we investigated the effect of a number of dopants (lithium, silicon, ruthenium, molybdenum and tin) upon the transparency, crystallinity, porosity and conductivity of the modified films. Tin, molybdenum and silicon were shown to improve the electrochromic behaviour of the layers whereas ruthenium enhanced considerably the electronic conductivity of the WO₃ films. Interestingly, most of the dopants also affected the film morphology and the size of WO₃ nanocrystals. X-ray photoelectron spectra revealed absence of significant segregation of doping elements within the film. Raman analyses confirmed that the monoclinic structure of WO₃ films does not change upon substitutional cation doping; thus, the crystallinity of WO₃ films is maintained.     

Preparation and characterization of thin films of LaNiO3 for anode application in alkaline water electrolysis

LaNiO₃ electrodes were prepared, in the form of thin films on platinum by the methods of spray pyrolysis and sequential coating of mixed metal nitrate solutions followed by thermal decomposition. The films were adherent and of p-type semiconducting. Cyclic voltammetric studies indicated the formation of a quasireversible surface redox couple, Ni(iii)/Ni(ii), on these films before the onset of oxygen evolution in 1 m KOH. The anodic Tafel slopes were 40 and 65 mV decade^–1, on the sprayed LaNiO₃ film and on the film obtained by a layer method, respectively. The reaction order with respect to OH^– was found to be 2.2 on the sprayed oxide film and 1.2 on the layer film. The sprayed oxide film was found to be electrocatalytically more active. It is suggested that the oxygen evolution reaction proceeds on both the film electrodes via the formation of the physisorbed H₂O₂ as an intermediate in the rate determining step.     

Orientationally ordered and patterned discotic films and carbon films from liquid crystal precursors

This article demonstrates techniques for fabricating novel organic and carbon films, in which liquid crystal surface anchoring and flow are exploited to precisely control molecular structure (in organic films) or crystal structure (in carbon films). Surface anchoring states were first measured for AR mesophase on spin-coatable organic resins, including commercial polyimide and photoresist. These results were used to develop a lithographic technique for ordering AR surfaces in preprogrammed orientational micropatterns. AR was also processed into radial or star symmetry films by forced spreading combined with edge-on anchoring templates. Additional thin films were prepared from alternative liquid crystalline precursors composed of sulfonated polyaromatic dyes. These disk-like planar molecules undergo massive π-stacking in aqueous solution to form rod-like aggregates. At high concentrations or on surfaces, these rods or molecular columns align by repulsive interactions (lyotropic behavior), giving raise to a transverse alignment of the stacked polyaromatic disks. Here the lyotropic dye indanthrone disulfonate is used to make fully dense ordered carbon films by spin coating or Meyer-bar coating thin films on quartz followed by direct carbonization (without oxidative stabilization). These films exhibit surfaces rich in graphene edge-sites and are either anisotropic unidirectional (by bar coating) or multi-domain with long-range isotropy (by spin coating).     

Effect of precursors on the morphology and surface area of LaFeO3

Surface area and morphology of materials play an important role on their gas sensing performance because of the varying number and nature of adsorption sites. Current work reports a comparative study of LaFeO₃ synthesized by the facile hydrothermal method using two precursors; citric acid and KOH. The microstructure observed through FESEM and TEM showed different morphologies for the two precursors and calcination time (2?h & 6?h). Prior to calcination, higher surface area (50.54?m²/g) was obtained for LaFeO₃ prepared using KOH as compared to that for LaFeO₃ using citric acid (3.21?m²/g). Surface area increased from 3.21 to 7.06?m²/g for citric acid and decreased from 50.54 to 11.42?m²/g for KOH as calcination takes place for 6?h. Needle-shaped morphology of p-type LaFeO₃ with high surface area (50.54?m²/g) for KOH would provide large active sites which would enhance sensitivity towards gases. Hence, LaFeO₃ samples prepared using KOH with and without calcination are expected to give better performance for gas sensing than LaFeO₃ samples synthesized using citric acid.     

3D Hierarchical orientation in polymer-clay nanocomposite films

Organically modified clay was used as reinforcement for HDPE using maleated polyethylene (PEMA) as a compatibilizer. The effect of compatibilizer concentration on the orientation of various structural features in the polymer-layered silicate nanocomposite (PLSN) system was studied using two-dimensional (2D) small angle X-ray scattering (SAXS) and 2D wide-angle X-ray scattering (WAXS). The dispersion (repeat period) and three-dimensional (3D) orientations of six different structural features were easily identified:

(a)

clay clusters/tactoids (0.12 μm),

(b)

modified clay (002) (24-31 Å),

(c)

unmodified clay (002) (13 Å),

(d)

clay (110) and (020) planes normal to (b) and (c),

(e)

polymer crystalline lamellae (001) (190-260 Å), and

(f)

polymer unit cell (110) and (200) planes.

A 3D study of the relative orientation of this hierarchical morphology was carried out by measuring three scattering projections for each sample. Quantitative data on the orientation of these structural units in the nanocomposite film is determined through calculation of the major axis direction cosines and through a ternary, direction-cosine plot. Surprisingly, it is the unmodified clay which shows the most intimate relationship with the polymer crystalline lamellae in terms of orientation. Association between clay and polymer lamellae may be related to an observed increase in lamellar thickness in the composite films. Orientation relationships also reveal that the modified clay is associated with large-scale tactoid structures.     

Growth control of RF magnetron sputtered SrRuO3 thin films through the thickness of LaNiO3 seed layers

SrRuO₃ (SRO) thin films were grown on SiO₂/Si substrates with different thickness of LaNiO₃ (LNO) seed layers by RF magnetron sputtering. Effects of LNO thickness on the grain orientation, surface morphology, magnetic behavior and electrical transport properties of SRO films were investigated. The orientation of SRO films transformed from (110)_pc to (001)_pc and the residual stress was released gradually with increasing the thickness (pc refers to the pseudo-cubic unit cell of SrRuO₃). SRO films with higher orientation grown on LNO exhibited more flat surface, higher saturation magnetization, and lower coercive field. The magnetic anisotropy was enhanced on thicker LNO due to the different states of residual stress. In addition, the temperature dependence of resistivity was promoted by the microstructural disorder. (110)_pc-oriented SRO monolayer electrode and (001)_pc-oriented SRO/LNO300 bilayer electrode own low room temperature sheet resistance of 0.38 Ω/□ and 0.26 Ω/□, respectively. The results indicate that the controllable SRO films can be used as not only good bottom electrodes but also promising templates to control the crystallographic orientations of various other perovskite-based functional materials.     

Ultraviolet pulsed laser crystallization of Ba0.8Sr0.2TiO3 films on LaNiO3-coated silicon substrates

In this work, Ba_0.8Sr_0.2TiO₃ (BST) films on LaNiO₃-buffered SiO₂/Si (LNO/SiO₂/Si) substrates were crystallized by pulsed laser irradiation. Solution-derived amorphous barium–strontium–titanate precursor layers were crystallized with a KrF excimer laser in oxygen ambient at fluences ranging from 50 to 75 mJ cm⁻². With the substrate temperature set to 500 °C, the number of pulses and film thickness were varied until high-quality crystallinity could be achieved. It was found that films with a thickness of 40 nm are fully crystallized with a uniaxial {00l} orientation which is predetermined by the LaNiO₃ orientation. On the other hand, for 160 nm thick films, crystallization was observed after 12,000 pulses in the 70 nm close to the surface, while the rest of the film remained amorphous. The large temperature difference between the film surface and interface due to the low thermal conductivity of the amorphous BST is suggested as the origin of this behavior. Films thicker than 80 nm cracked on crystallization due to the stress caused by the different thermal expansion coefficients of film and substrate, as well as the large temperature variations within the BST film.     

Microcellular polymeric materials from microemulsions: Control of microstructure and morphology

The effect of a crosslinking agent on the formation of porous solids by polymerizing microemulsions formulated with monomers was investigated. Phenomenological studies were carried out to evaluate the possibility of controlling the morphology of the porous polymeric materials by using precursor microemulsions having a distinct microstructure. A microemulsion system, containing methyl methacrylate (MMA), acrylic acid (AA), the crosslinking agent ethyleneglycol dimethacrylate (EGDMA), water, and sodium dodecylsulfate (SDS) as surfactant, was studied. An identical surfactant-free system, formed using the same monomers, crosslinking agent, and water, but without surfactant, was also studied. Microemulsion samples from both these systems, having a water in oil droplet microstructure and also samples exhibiting bicontinuous microstructural characteristics, were used as precursor systems for polymerization. The morphology of the polymeric solids obtained was examined using scanning electron microscopy and thermogravimetric analysis. The results of this study indicate the possibility of forming porous polymeric solids having specifically tailored morphology and microstructure by the polymerization of monomer containing microemulsions. © 1993 John Wiley & Sons, Inc.     

Characterization of multiferroic PbFe0.5Nb0.5O3 and PbFe0.5Ta0.5O3 ceramics derived from citrate polymeric precursors

Ceramics of the perovskite multiferroics PbFe_0.5Nb_0.5O₃ (PFN) and PbFe_0.5Ta_0.5O₃ (PFT) were synthesized from new citrate polymeric precursors. X-ray tests pointed to trace amounts of the pyrochlore phase. SEM studies revealed the heterogeneous grain size distribution for PFN and the homogeneous one for PFT. Dielectric studies pointed to one diffuse T-C phase transition at 378 K for PFN and two diffuse M-T and T-C phase transitions, at 200 and 235 K, for PFT, respectively. X-ray photoelectron spectroscopy studies of PFN reveal that all ions exist in one valence state, however, with two chemical shifts for Pb²⁺. Two valence states for the majority of ions of PFT seem to be connected with a higher volume fraction of the amorphous grain-boundary phase. The electronic energy band gap for both compounds is approximately 2.8 eV. Two magnetic transitions, ie, from the paramagnetic to the antiferromagnetic phase and then to the spin-glass phase, were observed at 156 and 10 K for PFN, and at 145 and 15 K for PFT, respectively.     

Spray coating thin polymeric sensor films for Au3+

A novel polymeric sensor of the poly(sodium-4-styrenesulfonate) (PSS)-modified rhodamine B derivative (Rho) was synthesized using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC)/N,N′-dimethylpyridin-4-amine (DMAP) as coupling reagents to obtain PSS-Rho4 in 21% yield. The characterization and “Off–On” sensing phenomena were established through UV–Vis, fluorescence, NMR, and FTIR techniques. The PSS-Rho4 showed high selectivity and sensitivity for Au³⁺ over other metal ions. Upon the addition of Au³⁺, significant color change and “Off–On” fluorescence were observed due to a cation Au³⁺ induced spirolactam ring-opening process with detection limit down to micromolar values (1.2 μM). In addition, spray coating thin polymeric sensor films were produced onto the surface of material (PSS-Rho4-ITO and PSS-Rho4-filtered paper) providing a fast, portable, and easy-to-use molecular device for the detection of Au³⁺ in the real system. Reversibility was evaluated by rinsing with EDTA solution under basic condition. We believe that, this approach provides a sensitive and accurate method for the detection of Au³⁺ in environmental and biological applications. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48273.     

钙钛矿型LaNiO_3纳米粉体的制备及表征

以硝酸盐为原料、柠檬酸为络合剂,采用柠檬酸络合分解法制取了LaNiO3的前躯体,后经高温煅烧得到单相钙钛矿型的LaNiO3纳米级粉末。利用XRD、SEM等手段对其结构及形貌进行表征,结果表明所得到的LaNiO3颗粒大小约为50～80nm。     

Honeycomb-like polymeric films from dendritic polymers presenting reactive pendent moieties

In this paper we describe the fabrication of honeycomb-shaped polyurethane films from dendritic side-chain polymers presenting reactive pendent units. Two novel functional polyurethanes, poly(urethane-co-acylurea) (PU-PACY) and polyurethane-co-azetidine-2,4-dione containing polyurethane (PU-PAZ), were synthesized. The waxy dendrons featured focal urea/malonamide linkages favorable for hydrogen bonding and peripheral alkyl chains. These intermolecular forces caused two functional PUs to undergo phase separation and self-assembly. This resulted in honeycomb-like films with well-controlled surface roughness characterized in terms of the ratio of rim width (W) to the pore size (D), i.e. W/D. The PU-PAZ film had a higher contact angle (CA) and a lower value of W/D than did the PU-PACY analogue, due to the presence of relatively more hydrophobic azetidine-2, 4-dione functionalities in the former film. Subsequent chemical modification of the PU-PAZ films through reaction with a hydrophobic poly(oxyalkylene)amine enhanced the CA from 113 to 134°. Further physical modification through a peeling-off process rendered the film surface with a three-dimensional (3D) rod-co-valley-structure having feature dimensions on a submicrometer scale. The 3D rod-co-valley–like film exhibited superhydrophobicity with a CA of 151°. The films also displayed excellent solvent-resistance after crosslinking with a diamine. Through hydrophobic or hydrophilic chemical modification, we could readily manipulate the surface properties of these honeycomb-like films with controllable surface roughnesses and reactive functionalities.     

Microstructure of LaNiO3 thin films obtained by the spin-on technique from citrate precursors

The morphology of perovskite LaNiO₃ (LNO) thin films is a very important feature considering the fact that they could be used as an electrode material in ferroelectric devices. In this work, LNO films were prepared from citrate precursors. The films were deposited on Si (100) and Pt covered Si substrates [Pt (111)/Ti/SiO₂/Si] using the spin-on technique. The phase composition of the films was confirmed by X-ray powder diffraction analysis, while the microstructures were investigated by atomic force microscopy. The influence of the metal ion:citric acid:ethylene glycol ratio on the morphology of the films was investigated. After optimization of these parameters, very homogenous, uniform and crack-free LNO films were obtained.     

Deposition of carbon nitride films from single-source s-triazine precursors

Trisubsituted derivatives of s-triazine (1,3,5-triazine) with N(i-Pr)₂, N(i-Bu)₂, NH(t-Bu), pyridyl, and NHNHMe ligands were used as single-source precursors to produce carbon nitride (CN_x) thin films via hot wall CVD. The precursors are either commercially available or were synthesized in straightforward, one-pot procedures, and the synthesis and characterization of tris-2,4,6-methlyhydrazino-1,3,5-triazine (TMHT) is reported for the first time. All of the precursors studied are thermally stable and volatilize below 250 °C. They thermally decompose between 500 and 1000 °C, resulting in CN_x films with x ranging from 0.95 to 0.03. The film deposition temperature and nitrogen content depend upon the structure and stability of the precursor. The film properties vary from disordered insulating structures with high nitrogen content (CN_0.95) to low nitrogen content turbostratic carbon films. The films on Si and SiO₂ substrates were characterized by Auger surface analysis, FT-IR and Raman spectroscopy, X-ray diffraction, and scanning electron microscopy.     

Production of hydrogen and MWCNTs by methane decomposition over catalysts originated from LaNiO3 perovskite

LaNiO₃ type perovskite was prepared by the “self-combustion” method and was used as catalyst precursor for the methane decomposition reaction at 600 and 700 °C. CH₄ conversion reaches 80% at 700 °C and 65% at 600 °C using pure CH₄. The yield of CNT and H₂ were 2.2 g_CNT g^?1 h^?1 and 8.2 L g^?1 h^?1 at 700 °C respectively after 4 h of reaction. When the reaction is prolonged to 22 h the catalytic activity decreases but the catalyst is still active, the production of hydrogen reaches 63.5 L (STP) per gram of catalyst and the production of MWCNT was equal to 17 g per gram of catalyst.Multi-wall carbon nanotubes were characterized by X-ray diffraction (XRD), surface area (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and Raman spectroscopy. TEM micrographs showed that MWCNT longer than 20 μm were formed with inner diameters ranging from 5 to 16 nm and outer diameters up to about 40 nm.The results obtained here clearly show that the use of the perovskite LaNiO₃ as catalytic precursor is very effective for the simultaneous production of carbon nanotubes and hydrogen.