The silane coupling agent 3-aminopropyltriethoxysilane (KH-550) was used to modify the surface of two kinds of high-performance polyimide (PI) fibres (i.e., PI-1 and PI-2). The surface chemical composition, morphologies and roughness of modified PI fibres were characterised by XPS, SEM and AFM. Results showed that the elemental ratio between O and C, the surface oxygen concentration and the surface roughness increased with KH-550 concentration. However, the interfacial shear strength (IFSS) and interlaminar shear strength (ILSS) values of PI fibre/epoxy resin composites increased and then decreased with KH-550 concentration. When KH-550 concentration was increased to 4 wt%, the IFSS and ILSS values reached their maximum point. At this point, the IFSS values were found increase by 17.3% and 8.3% for PI-1 and PI-2, respectively, compared with their pristine state. Meanwhile, the ILSS values of PI-1- and PI-2-reinforced composites were found increase by 22.4% and 24.1%, respectively.

ABSTRACTA series of novel ultralow dielectric porous polyimide (PI) films containing adamantane groups was prepared via the thermolysis of polyethylene glycol (PEG) oligomers mixed into PI matrix. Scanning electron microscopy results indicated that the porous PI films showed closed pores with an average diameter of 120 ± 10 nm. Good thermal properties with 5% weight loss temperature of 499 °C in air atmosphere and glass transition temperature in excess of 310 °C were shown for porous PI films. Notably, the ultralow dielectric constant of porous PI films with 1.85 at 1 MHz was obtained and revealed via broadband dielectric spectroscopy. The effects of the chemical structure of the PI matrix and PEG content on the decomposition behavior of PEG and the performance of porous films were investigated. Wide‐angle X‐ray diffraction results indicated that the PI matrix with large d‐spacing generated weaker interactions between the PEG and PI backbone than those of PI matrix with small d‐spacing. As a result, the PEG for the PI matrix with large d‐spacing was completely decomposed. As indicated by the broadband dielectric spectroscopy results, lower dielectric porous PI films were prepared when the PEG contents in the PI matrix increased from 0 to 20 wt %. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018, 56, 549–559

The synthesis and characterization of oligoaniline-containing dendron-rod-dendron dumbbell shape block oligomer (14G3A7) are presented. The unusual surface morphological evolution from fibrils to flat single-layer film and to a porous network is observed for 14G3A7 simply by oxidizing the block oligomer in solution. Based on the analysis of cryo-TEM as well as comparative studies on solution concentration and substrate properties, the series of changes in the surface morphology are explained through aniline conformational transition during oxidation. The network self-assembled from oxidized 14G3A7 contains a two dimensional close packing skeleton of aniline segment, which may find a wide range of applications in electronic sensitive devices.

Dendronized polymer (DP) gelators were prepared via complexation of a dendritic gelator of the poly(urethane amide) dendron, which contains an ionizing carboxyl group on the apexes, with three positively charged polyelectrolytes. All these complexes could form organogels in toluene, and their gel properties were studied through determination of their minimum gelation concentration and characterization of the networked supramolecular structures formed in their gel-phase using TEM, AFM and SAXS. Our findings showed great differences in the gel-forming ability and supramolecular structure among these gelators. A simple simulation on the conformations of the three polyelectrolytes illustrated that the differences came mainly from the polyelectrolyte conformations which produced different distribution and orientation of the dendritic gelators along the backbones. When the backbone could induce the dendritic gelators to form a pre-ordered structure before gelation, the DP gelator would form nice supramolecular aggregates showing an enhanced gel-forming ability. Without this, the gel-forming ability would not be enhanced.

Novel dendritic triblock co-oligomer (14G2A3) consisting of ester dendrons and aniline oligomer was synthesized and found to self-assemble into fibrils in THF. Studies reveal that the formation of the fibrils originates from both of the amphiphilic interactions between the ester dendrons and oligoaniline, as well as the intermolecular π-π stacking among oligoanilines. The shape effect of dendrons on molecular packing was comparatively analyzed with packing parameter against its linear analogous compound. At the same time, the driving forces that dominate the final aggregating state of the block oligomer were separately investigated using the bulky-group protecting method, which allows release of the intermolecular π-π stacking of oligoaniline in a controlled manner. Results show that both the introduction of dendrons and the intermolecular π-π stacking will increase the packing parameter of the block oligomer and, consequently, cause the self-assembly morphology to evolve step by step from micelles to vesicles and finally to fibrils. The fibrils can form complexes with SWNTs to increase solubility in THF. The effective fluorescence quenching accompanied also opens a gate for the block co-oligomer to have potential applications in organic electronic devices.

In a previous paper, we investigated the solvent-induced crystallization of films made up of spherical micelles, which were prepared by mixing polystyrene-block-poly(acrylic acid) and polystyrene-block-poly(2-vinylpyridine)-block-poly(ethylene oxide) in the neutral solvent N,N-dimethylformamide (DMF). In the work reported in the present paper, we further studied the cylinder-to-rod-to-sphere evolution of complex micelles in solution and their corresponding solvent-induced crystallization process. The initial morphology of the micelles in the solution was cylindrical due to a rapid growth of micelles with high unimer concentration, and spheres became the dominant form after storage at room temperature for a longer time. Regular square platelets can form after a certain period of treatment for all micelles in DMF vapor for sufficient time. However, the kinetics of their solvent-induced crystallization process is quite different. The aggregation and subsequent nucleation of poly(ethylene oxide) blocks are determined by the distribution of crystallizable poly(ethylene oxide) blocks in the films. (C) 2010 Society of Chemical Industry

The mechanisms for introduction of the additive to improve the poly(3-hexylthiophene) (P3HT):methanofullerene [6,6]-phenyl C61-butyric acid methyl ester (PCBM) organic solar cells performance are investigated. We add n-dodecylthiol to P3HT/PCBM solution and find that it both improves P3HT crystallinity and enhances P3HT/PCBM phase separation extent. UV–vis absorption spectroscopy (UV–vis) and dynamic light scattering (DLS) results reveal that n-dodecylthiol reduces the P3HT chains entanglement in the solution, which facilitates coil-to-rod transformation, a premise condition for P3HT crystallization. Also, it discloses that the influence of PCBM on the P3HT molecular interaction is diminished by adding n-dodecylthiol, this consequently benefits the P3HT crystallization during the film-forming process. Furthermore, the enhanced P3HT crystallinity reduces the PCBM amount which dissolved in the amorphous regions of P3HT, then promotes the aggregation of PCBM, which contributes to the controlled scale of phase segregation. Thus an increased P3HT crystallinity and a commensurate scale of phase separation balancing for exciton dissociation and charge transport and/or collection are finally obtained. This results in an almost threefold increase in device efficiencies when the volume fraction of additive is 2.0%, compared with reference devices without any additive in the photoactive layer as a consequence.

Novel π-conjugated coil-rod-coil triblock oligomers containing optoelectronic active oligoaniline segments were synthesized. The block oligomer can self-assemble into diverse aggregating morphologies including spherical micelles and thin-layer vesicles in THF, which is found associated with the removing of the protecting groups of oligoaniline segments. A possible mechanism was proposed to explain the self-assembly behavior changes in which chain conformation variation of the aniline segments initiated from deprotection of the nitrogen atoms is pointed to be the key factor that dominates the transition process.

A new method of reversibly moving CdS nanoparticles in the perpendicular direction was developed on the basis of the phase separation of block copolymer brushes. Polystyrene-b-(poly(methyl methacrylate)-co-poly(cadmium dimethacrylate)) (PS-b-(PMMA-co-PCdMA)) brushes were grafted from the silicon wafer by surface-initiated atom transfer radical polymerization (ATRP). By exposing the polymer brushes to H2S gas, PS-b-(PMMA-co-PCdMA) brushes were converted to polystyrene-b-(poly(methyl methacrylate)-co-poly(methacrylic acid)(CdS)) (PS-b-(PMMA-co-PMAA(CdS))) brushes, in which CdS nanoparticles were chemically bonded by the carboxylic groups of PMAA segment. Alternating treatment of the PS-b-(PMMA-co-PMAA(CdS)) brushes by selective solvents for the outer block (a mixed solvent of acetone and ethanol) and the inner PS block (toluene) induced perpendicular phase separation of polymer brushes, which resulted in the reversible lifting and lowering of CdS nanoparticles in the perpendicular direction. The extent of movement can be adjusted by the relative thickness of two blocks of the polymer brushes.

Surface-tethered oppositely charged weak polyelectrolyte block copolymer brushes composed of poly(2-vinyl pyridine) (P2VP) and poly(acrylic acid) (PAA) were grown from the Si wafer by atom-transfer radical polymerization. The P2VP-b-PAA brushes were prepared through hydrolysis of the second PtBA block to the corresponding acrylic acid. The P2VP-b-PAA brushes with different PAA block length were obtained. The P2VP-b-PAA brushes revealed a unique reversible wetting behavior with pH. The difference between the solubility parameters for P2VP and PAA, the changes of surface chemical composition and surface roughness, and the reversible wetting behavior illustrated that the surface rearrangement occurred during treatment of the P2VP-b-PAA brushes by aqueous solution with different pH value. The reversible properties of the P2VP-b-PAA brushes can be used to regulate the adsorption of the sulfonated PS nanoparticles.

The self-assembly processes of the rod-coil diblock oligomer thin film of tetra-aniline (TANI)-block-poly(L-lactide) (PLLA) with different film thicknesses induced in the coil-selective solvent of acetone vapor at room temperature were studied. The morphologies of the oligomer films were determined by the film thickness. For the thicker film (232 nm), the nonextinct concentric ring-banded textures could form. While for the thinner and appropriate film (about 6 nm), multistacked diamond-shaped appearances with the periodic thickness being about 8.5 nm(6-nm-thick extended PLLA chain and 2.5-nm-thick p-pi conjugating TANI bimolecular layer) formed. The possible formation models of those two regular morphologies were presented in detail.

Tetraaniline-block-poly(L-lactide) diblock oligomers are synthesized via ring-opening polymerization. The diblock oligomers cast from all L-lactide selective solvent (chloroform) show spherical aggregates for the leucoemeraldine state, and ring-like structures that are composed of much smaller spherical aggregates for the emeraldine state. The formation mechanisms of the two different surface morphologies are discussed in detail.

In this paper, a simple route to the fabrication of palladium nanosheets is described. The interaction of palladium chloride (PdCl2) and n-octylamine salt resulted in the formation of a quasi-perovskite-type composite with a layered structure on a molecular scale. This composite can be employed as a template for preparing ultrathin Pd nanosheets when a {PdCl4}2− network is reduced in situ by hydrogen in toluene. The x-ray diffraction results indicate that the resulting Pd nanosheets are highly ordered, and they are confined inside the organic matrix as evidenced by high resolution transmission electron microscopy. These Pd nanosheets can be reorganized into layered structures in non-polarized organic solvent when the ordered structure is destroyed. This method of preparing Pd nanosheets is expected to be applicable to other layered organic/inorganic perovskite systems for obtaining the corresponding metal nanosheets.

The effects of molecular weight and concentration of poly (methyl methacrylate) (PMMA) homopolymer or symmetric short polystyrene-block-poly (methyl methacrylate) (PS-b-PMMA) diblock copolymer on the size of the nanostructures of its blends with symmetric long PS-b-PMMA diblock copolymer have been investigated by atomic force microscopy. By careful controlling of the film thickness, solvent selectivity, and annealing time, PMMA cylindrical microdomains oriented normal to the film surface were obtained in all thin films. With the addition of both low- and high-molecular-weight PMMA homopolymers, the cylindrical domain sizes increased although it was less obvious for the lower molecular weight homopolymer. In contrast to the homopolymer, adding the short chain diblock copolymer resulted in a decrease in the cylindrical domain size, which was ascribed to the reduction of the interfacial tension and increase in the stretching energy.

Spherical SiO2 particles have been coated with Y2O3:Eu3+ phosphor layers (SiO2@Y2O3:Eu3+) by a Pechini sol-gel process. X-ray diffraction, field emission scanning electron microscopy, transmission electron microscopy, photoluminescence, and cathodoluminescence spectra were utilized to characterize the SiO2@Y2O3:Eu3+ core-shell-structured phosphor particles. The obtained core-shell phosphors consist of well dispersed submicron spherical particles with narrow size distribution. The thickness of Y2O3:Eu3+ shell could be easily controlled by changing the number of deposition cycles (60nm for three deposition cycles). The SiO2@Y2O3:Eu3+ core-shell particles show a strong red emission corresponding to D05-F27 (611nm) of Eu3+ under the excitation of ultraviolet (250nm) and low-voltage electron beams (2–6kV), which have potential application for field emission displays.

We follow the time development of the micro-domain structure in symmetric polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer thin films during acetone vapor treatment. Besides the highly ordered nanoscopic spheres or stripes as reported previously, a novel so-called flower-like pattern, which comprises six PS spheres and each PS sphere belongs to three "flowers" is formed. This finding is very helpful to discuss the highly ordered nanoscopic sphere formation process.

The dewetting pattern development of thin film of poly(styrene)-block-poly(methyl methacrylate) (PS-b-PMMA) diblock copolymer has been studied after ‘annealing’ in the PMMA block selective solvent vapor. Initially, typical circular dewetted holes are observed. Further annealing, however, results in the formation of fractal-like holes. The heterogeneous stress induced by the residual solvent remaining in the film after spin-coating induces the anisotropy of the polymer mobility during the annealing process, which triggers the formation of the intriguing surface patterns.

Binary symmetric diblock copolymer blends, that is, low-molecular-weight poly(styrene-block-methyl methacrylate) (PS-b-PMMA) and high-molecular-weight poly(styrene-block-methacrylate) (PS-b-PMA), self-assemble on silicon substrates to form structures with highly ordered nanoholes in thin films. As a result of the chemically similar structure of the PMA and the PMMA block, the PMMA chain penetrates through the large PMA block that absorbs preferentially on the polar silicon substrate. This results in the formation of nanoholes in the PS continuous matrix.

We have studied a morphological instability of a double layer comprising the polymer film and air gap confined between the two plates set to different temperatures. The temperature gradient across the double layer causes the breakup of the polymer film into well-defined columnar, striped or spiral structures spanning the two plates. The pattern formation mechanisms have been discussed. The formed patterns can be transferred to produce PDMS stamp, a key element of soft lithography for future microfabrication.

Ordered hexagonal droplets patterns in phase-separating polymeric blend films of polystyrene and poly(2-vinylpyridine) (PS/PVP) formed due to the convection effect by solvent evaporation. The influences of PS molecular weight, solvent evaporation rate, and the weight ratio of PS to PVP on the PVP-rich domains pattern formation and distributions were investigated by atomic force microscope (AFM). Only in an appropriate range of molecular weight of PS, can the ordered pattern form. Too low or too high molecular weight of PS led no ordered pattern due to the viscosity effects. The increase of solvent evaporation rate decreased the mean radius of the PVP-rich domains and the intervals between the centers of the domains due to the enhancement of the viscosity on the top layer of the fluid film. The increase of the weight ratio of PS to PVP decreased mean radius of the PVP-rich domains whereas the intervals between the centers of droplets remained constant. Therefore, the size and the distributions of ordered patterns can be tuned by the polymer molecular weight, the weight ratio of the two components and the solvent evaporation rate. It revealed that the hydrodynamic effects played a significant role on the pattern formation and distributions.