Solvent vapor induced dewetting in diblock copolymer thin films

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.     

Composition effect on dewetting of ultrathin films of miscible polymer blend

Two kinds of dewetting and their transition induced by composition fluctuation due to different composition in blend [poly(methyl methacrylate) (PMMA) and poly(styrene-ran-acrylonitrile) (SAN)] films on SiO_x substrate at 145 °C have been studied by in-situ atomic force microscopy (AFM). The results showed that morphology and pathway of dewetting depended crucially on the composition. Possible reason is the variation in intensity of composition fluctuation resulted from the change of components in polymer blend. Based on the discussion of this fluctuation due to the composition gradient, parameter of U_q0/E, which describes the initial amplitude of the surface undulation and original thickness of film respectively, has been employed to distinguish the morphologies of spontaneous dewetting including bicontinuous structures and holes. Prior to the investigation of dewetting, it is confirmed that this blend is miscible at 145 °C using grazing incidence ultra small-angle X-ray scattering (GIUSAX).     

Silicon and carbon substrates induced arrangement changes in poly(styrene-b-isoprene-b-styrene) block copolymer thin films

Poly(styrene-b-isoprene-b-styrene) (SIS) block copolymer ordering in thin films was studied using two selective substrates as carbon and silicon. Atomic force microscopy (AFM) and contact angle measurements were employed to examine the affinities between domains and surrounding interfaces. The surface morphology was examined by AFM using different amplitude ratios. Results showed polyisoprene (PI) domain layer formation in the outermost film layer. On the other hand, the layer close to substrate adopted different arrangements on silicon and carbon substrates. Topographical and phase images revealed that in both substrates with the thickest films, the interactions between substrate and block domains were not enough to induce surface ordering being the morphology independent of employed substrate. However, decreasing film thickness, SIS thin films displayed a variety of arrangements such as perforated lamellae and cylindrical morphologies. Depending on substrate, these morphologies were achieved in different film thicknesses. Finally, the thinnest film did not adjust to characteristic domain spacing commensurability and terraces formation was observed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Water-induced morphology evolution of block copolymer micellar thin films

Morphology evolution of diblock copolymer polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) micellar thin film in the presence of water was investigated. Surface holes with nanoscale cavities in hexagonal order could be induced by water treatment for certain periods. The nanoscale surface cavities could be transformed into isolated nanospheres in a dry environment or back to protruding densely packed spheres by toluene (a selective solvent for PS coronae) treatment. The morphology evolution of micellar thin film strongly depended on the slow evaporation of toluene solvent, the swelling of P4VP cores in the humid environment, and the subsequent movement of PS chains induced by air and toluene. The incompatibility between solvent and block, and that between the unlike blocks also played an important role in the morphology evolution.     

The nanostructure and dewetting of block copolymer thin films annealed in different neutral solvents

The morphology of polystyrene‐b‐poly(2‐vinyl pyridine) thin films annealed under various neutral solvents was investigated. The morphological transition depends on the vapor pressure of the solvent, the quantity of the solvent in the film, and annealing time. We introduced the volume fraction of solvent in a film (Q) to correlate these factors to the morphology. At low Q, the amount of solvent that penetrates into the film is limited and it cannot induce enough chain mobility. Thus, thin film shows short stripes or a worm‐like structure. At high Q, the great diffusion of solvent into the film facilitates polymer mobility, leading to an ordered structure. Our results also suggested that the dewetting mechanism of thin film depends on Q. At low Q, dewetting develops via the nucleation and growth. At high Q, the condensation of solvent on the surface removes some polymer and dewetting is dominated by spinodal mechanism. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Morphology of an asymmetric ethyleneoxide-butadiene di-block copolymer in bulk and thin films

We present experiments on the melt and crystal morphology of a asymmetric semi-crystalline poly(ethylene/butylene-b-ethyleneoxide) diblock copolymer (PB_h-b-PEO) in bulk as well as in thin films. Simultaneous small- and wide-angle X-ray scattering combined with AFM and TEM images reveal in the melt a bulk morphology of hexagonally packed cylinders of PEO in a PB_h matrix, that transforms into a hexagonal perforated lamellar phase upon crystallization. X-ray reflectivity of thin films of PB_h-b-PEO in the melt indicates wetting layers at the top and bottom interfaces, which force the cylinders in the interior to orient parallel to the substrate. Crystallization of the PEO block leads to roughening of the air/film interface and causes lateral structuring coexisting with planar lamellar layers in thinner films.     

Synthesis of novel CuS with hierarchical structures and its application in lithium-ion batteries

Novel sphere-like CuS hierarchical structures are fabricated by solvothermal approach without any surfactant and template. SEM and TEM characterizations show that the CuS sphere-like structures are composed of tens to hundreds of well-arranged and self-assembled nanoplates with a thickness of about 20 nm. The effects of dosage of CuCl₂•6H₂O, temperature and reaction time on the morphology of the products are systematically investigated and the results indicate that the CuS sphere-like hierarchical structures can only be obtained under certain experimental conditions. The possible formation mechanism of the CuS hierarchical structures is proposed. In addition, the possibility of using CuS as the electrode material for lithium ion batteries is studied.     

Microwave absorbing property of gelcasting SiC-Si3N4 ceramics with hierarchical pore structures

In this work, X-band microwave absorbing properties of gelcasted SiC-Si₃N₄ ceramics with different hierarchical pore structures at both room temperature and high temperature were reported for the first time. Effects of pore structures, sample thickness and temperature on complex permittivity and microwave absorption performance of SiC-Si₃N₄ ceramics were investigated systemically. The results suggested that the introduction of appropriate hierarchical pore structure was beneficial to improve the absorbing performance of the material. The minimum reflection loss value can reach -59.2 dB for the 3.8 mm thick sample at 8.35 GHz and room temperature. By elevating the temperature, the effective absorption bandwidth of porous SiC-Si₃N₄ with a thickness of 3.0 mm covers the entire X-band. The excellent microwave absorbing property of porous SiC-Si₃N₄ ceramics was attributed to the multiple reflections brought about by the existence of hierarchical pores, interfacial polarization between SiC and Si₃N₄ grains, and defect dipole polarization in grains and grain boundaries. The good absorbing property and the clarification of absorbing mechanism of porous gelcasted SiC-Si₃N₄ ceramics will provide a solid foundation for the development of porous SiC-based absorbing parts.     

生物可降解两亲性嵌段共聚物胶束的制备及其对叶酸的控制释放

以甲氧基聚乙二醇(mPEG)为引发剂,在辛酸亚锡催化下引发ε-环己内酯(CL)开环聚合,合成了聚乙二醇-聚己内酯两亲性嵌段共聚物(mPEG-PCL)。通过FTIR、1H-NMR及GPC等表征手段确定了mPEG-PCL的组成及结构。采用芘荧光探针法、透射电镜和动态激光光散射研究了聚合物在水中的自组装行为。结果表明:聚合物在水溶液中能够自组装形成粒径小于100 nm的规则球状胶束,且具有较低的临界胶束浓度(7.35×10-3 g/L);模型药物(叶酸)成功负载于聚合物纳米胶束内,并且能延缓叶酸的释放,其释药速率受载药量和释放介质pH的影响。     

Foam-gelcasting preparation,microstructure and thermal insulation performance of porous diatomite ceramics with hierarchical pore structures

Hierarchically pore-structured porous diatomite ceramics containing 82.9∼84.5% porosity were successfully prepared for the first time via foam-gelcasting using diatomite powder as the main raw material. Sizes of mesopores derived from the raw material and macropores formed mainly from foaming were 0.02∼0.1 μm and 109.7∼130.5 μm, respectively. The effect of sintering temperature, additive content and solid loading of slurry on pore size and distribution, and mechanical and thermal properties of as-prepared porous ceramics were investigated. Compressive strength of as-prepared porous ceramics increased with sintering temperature, and the one containing 82.9% porosity showed the highest compressive strength of 2.1 ± 0.14 MPa. In addition, the one containing 84.5% porosity and having compressive strength of 1.1 ± 0.07 MPa showed the lowest thermal conductivity of 0.097 ± 0.001 W/(m·K) at a test temperature of 200 ̊C, suggesting that as-prepared porous ceramics could be potentially used as good thermal insulation materials.     

A feasible method of preparation of block copolymer latex films with stable microphase separation structures

RAFT (reversible addition–fragmentation chain transfer) miniemulsion polymerization was engaged to engineer latex particle morphology. With this approach, a macromolecular amphiphilic RAFT agent with epoxy groups was synthesized that assembled onto the surface of monomer mini-droplets. It caused the polymer chains to grow inwards gradually in particles as polymerization proceeded. The batch polymerization of n-butyl acrylate (BA) followed by addition of styrene (St) led to the formation of PBA-b-PSt diblock copolymer shell–core latex, where epoxy groups were enriched on the particle surface. The shell–core ratio was varied feasibly by changing the mass of St. When the structured latexes were dried, epoxy groups underwent efficient curing reactions triggered by a thermal-latent curing agent (dicyandiamide) in a controlled manner, leading to the formation of bonded PBA blocks connecting the PSt blocks in adjacent particles. Mechanical tests show that the films behaved like ductile materials, whose modulus and elongation at break were functions of copolymer compositions. Furthermore, curing reaction was a very robust method of preserving film morphology which correlated well with that observed for the latex particles. The results demonstrated a feasible method of preparation of latex films with stable microphase separation structures and thus improved mechanical properties.     

Influence of segmental swelling of an asymmetric block copolymer on the morphology of melt-mixed immiscible polymer blends

We investigate the influence of an asymmetric PS-b-PMMA block copolymer (bcp) on the morphology of melt-mixed immiscible binary polymer blends containing poly(styrene-co-acrylonitrile) random copolymer (SAN) and poly(cyclohexylmethacrylate) (PCHMA). By varying the SAN copolymer composition, the balance between the swelling of each block segment located at the interface between the two phases is altered and the effect on blend morphology is studied. As in earlier studies using a symmetric bcp, we find that for a specified shear history, there is a zone of effective emulsification of the blend bounded by regions of internal and external emulsification failure. However, the locations of the boundaries between stable and unstable emulsification differ for an asymmetric versus a symmetric bcp. Thus the morphology depends not only on the segmental swelling ratio but also on the difference in the effective size of each bcp segment. Scaling arguments successfully correlate the limits of stable emulsification for both symmetric and asymmetric bcp.     

Study of the time evolution of the surface morphology of thin asymmetric diblock copolymer films under solvent vapor

The time development of the surface morphology of asymmetric polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) thin films ‘annealing’ in methanol vapor, a selective solvent for minority P4VP block, was investigated by atomic force microscopy(AFM). For PS-b-P4VP with cylindrical structure in bulk, as annealing time progressed, the surface morphology underwent structural transitions from featureless topography to hybrid morphology of cylindrical and spherical pits, to cylinders, to nanoscale depressions, back to cylinders again. The different film thickness made the number of the transitions observed, at any given annealing time, different. The thicker the film is the more transitions at a given annealing time can be observed. If the film was not thick enough, depressions appeared. For PS-b-P4VP with spherical structure in bulk, it displayed nanoscale depressions with the annealing time increasing. A possible mechanism of the transition of morphologies during solvent annealing was proposed.     

Perpendicular oriented cylinders via directional coalescence of spheres embedded in block copolymer films induced by solvent annealing

Polystyrene-b-poly(methyl acrylate) (PS-b-PMA) block copolymer with PS volume fraction of 25.2 vol% was synthesized by atom transfer radical polymerization. Non-pretreated silicon wafers were used as the substrates to prepare perpendicular oriented PS cylinders in PMA matrix via solvent annealing which could induce the transformation of spheres to vertically oriented and hexagonally packed cylinders. The spherical microdomains were formed after the evaporation of solvents from the solutions of the block copolymer in selective solvents mixed from methanol, acetone and dichloromethane. The thickness of films could be as thick as 1000 nm, which were much thicker than usual cases and the cylinders came from the directional coalescence of the spheres, thus any pre-treatments of the substrates were not required for perpendicular orientation. The structures were characterized by small angle X-ray scattering (SAXS), transmission electron microscope (TEM), atom force microscopy (AFM) and grazing incidence small angle X-ray scattering (GISAXS).     

苯乙烯-丁二烯-苯乙烯嵌段共聚物的环氧化研究

采用甲酸和过氧化氢（H2O2）原位生成的过氧甲酸对苯乙烯-丁二烯-苯乙烯（SBS）进行环氧化改性，制备了环氧化SBS（ESBS）。研究了原料摩尔配比及工艺条件对其环氧基质量分数的影响，利用GPC、FT—IR、^1H—NMR等手段对ESBS的结构进行了表征。结果表明，丁二烯链段上双键的反应活性大小次序为：顺-1，4-结构〉反-1，4-结构〉1，2-结构。在SBS的环氧化反应过程中，会伴有少量环氧基发生开环副反应。当SBS中C—C双键、甲酸和H202的物质的量配比为1／0．5／0．6，反应时间为2h，反应温度为60℃时，ESBS的环氧基质量分数最高，达到了18．1％。在体系中加入少量的聚乙二醇，有利于ESBS环氧慕盾量务教的提高．     

Microstructure evolution and cation interdiffusion in thin Gd2O3 films on CeO2 substrates

Thin Gd₂O₃ films with a thickness of about 150 nm were deposited by pulsed layer deposition on polycrystalline CeO₂ substrates to study the structural evolution of the Ce_1−xGd_xO_2−x/2 system with respect to phase formation and cation interdiffusion in the temperature range between 986 °C and 1270 °C. Transmission electron microscopy combined with quantitative energy dispersive X-ray spectroscopy was applied to study the microstructure and to obtain composition profiles across the Gd₂O₃/CeO₂-interface. Gd₂O₃ was observed to occur in the bixbyite structure up to 1175 °C. The fluorite and the bixbyite phase are found at intermediate compositions without any indication for a miscibility gap. Interdiffusion coefficients were obtained from Gd₂O₃/CeO₂-concentration profiles on the basis of the diffusion-couple solution of the diffusion equation. The activation enthalpy and frequency factor of the diffusion coefficient were derived assuming an Arrhenius-type behavior in the investigated temperature range.     

Morphology of semicrystalline oxyethylene/oxybutylene block copolymer thin films on mica

The morphology of as-cast and annealed thin films of four symmetric semicrystalline block copolymers on mica was investigated by tapping mode atomic force microscopy (AFM) and grazing incidence X-ray diffraction (XRD). It is found that the morphology of the thin films is dependent on chain length of oxyethylene/oxybutylene block copolymers. The as-cast thin films of the shorter E_mB_n block copolymers on mica exhibit a multi-layered lamellar structure parallel to the surface, in which the stems of the E crystals in the first half polymer layer contacting mica are parallel to the mica surface and perpendicular to the mica surface in the upper polymer layers. In contrast, the as-cast thin film of longer E₂₂₄B₁₁₄ exhibits a structure with mixed orientations of lamellar microdomains on a half polymer layer parallel to the surface. After annealing, the multi-layered structure on mica is transformed into a half-layered, densely branched structure, which is formed following a diffusion-limited aggregation mechanism, opposed to the featureless half-layered structure on silicon. Upon annealing, the upper polymer layers gradually retreat and the remaining area becomes thicker, but in contrast the first half polymer layer contacting mica becomes thinner due to wetting and the parallel orientation of the E crystal stems. The densely branched structure and the different chain orientations of the E crystal stems in the first half polymer layer contacting mica are attributed to the strong interaction between the E block and mica, as revealed by our previous work. The width of branches was employed to analyze the kinetics of secondary crystallization. It is also found that the width of the branches and the velocity of crystal front decrease as the chain length increases.     

Mechanisms of ordering in block copolymer sub-monolayer films upon selective solvent annealing

The solvent annealing induced two-dimensional ordering in poly(styrene–ethylene/butylenes–styrene) (SEBS) triblock copolymer sub-monolayer films with a thickness of 16 nm equaling half of the bulk domain thickness l₀ was investigated by time-resolved ex-situ atomic force microscopy (AFM). Cyclohexane, a selective solvent for majority poly(ethylene/butylenes) block was used. The detailed pathway information on the ordering of highly regular hexagonal spheres was obtained by repeatedly taking images of the same marked area on the sample surface after ex-situ annealing treatments. Two different ordering mechanisms were observed under two different solvent annealing conditions: 1) under a well-sealed environment with a slow cyclohexane evaporation rate, poorly-ordered short cylinders first break into spheres, then the evolution of spherical phase takes place to gradually improve the orderliness of spheres, and finally well-ordered hexagonal spheres are formed; 2) under a poorly-sealed environment with a fast cyclohexane evaporation rate, “holes” and “islands” are instantaneously formed on the sample surface first, and then the surface gradually get even annihilating hole and island areas. Within the hole areas, the transition from short cylinders to hexagonal spheres takes place via a not well-defined microphase separation structure, while in the island areas, the transitions between cylinders and spheres take place to improve the orderliness of cylinders, and finally the enough-ordered cylinders transform into hex-spheres.     

Fabrication of abrasion-resistant micro-nano hierarchical structure on glass surface by a hydrothermal corrosion method

When applying an additional coating method to fabricate micro-nano hierarchical structure required for superhydrophobic function on glass surface, the hierarchical structure does generally not have good abrasion resistance, due to the weak adhesion between coating and glass surface. However, glass itself is a material with good abrasion resistance. A micro-nano hierarchical structure with honeycomb-shaped micro-armor protection on glass surface by a two-step hydrothermal corrosion method has been constructed: the first step of hydrothermal corrosion in water to construct micro-armor structure, and the second step of hydrothermal corrosion in sodium citrate aqueous solution to fabricate micro-nano hierarchical structure. The advantages of this new method are: the treatment process is simple, and there is no need to apply additional coatings. The micro-nano hierarchical structure constructed on glass surface by this method has a great abrasion resistance. After 1,000 cycles of abrasion under harsh conditions, the nano-structure on glass surface can still be remained intact. It provides a new method for fabricating abrasion-resistant micro-nano hierarchical structure on glass surface, as well as a new approach to the preparation of abrasion-resistant superhydrophobic glass.     

Effect of graphene thickness on the morphology evolution of hierarchical NiCoO2 architectures and their superior supercapacitance performance

The rational design of electrode materials with special hierarchical architectures which possess both high surface area and conductivity is significant to enhance the performance of supercapacitors. Herein, hierarchical NiCoO₂ architectures assembled by ultrathin mesoporous nanosheets are in-situ grown on graphene@Ni foam (G@NF) by a template-free solvothermal route and subsequent annealing process, which is used as self-supported and binder-free supercapacitor electrodes. The effect of graphene thickness on morphology evolution of NiCoO₂ is investigated. Benefiting from the synergistic effect between graphene with remarkable conductivity and hierarchical NiCoO₂ architectures with high specific capacity, the NiCoO₂/G@NF electrodes show greatly improved electrochemical performance compared to NiCoO₂@NF and G@NF. The optimized NiCoO₂/G@NF has a specific capacitance of 1220 F/g at 1 A/g. While the NiCoO₂@NF and G@NF are only 565 and 151 F/g, respectively. The optimized NiCoO₂/G@NF remains 840 F/g at 20 A/g, revealing a remarkable rate performance (69% capacity retention from 1 to 20 A/g). Moreover, an outstanding cyclic stability of 80% capacitance retention can be obtained after 5000 charge/discharge cycles at 10 A/g, whereas the NiCoO₂@NF is only 46.5%. These results suggest that the hierarchical NiCoO₂ architectures/graphene hybrids are good candidates as effective electrode materials for supercapacitors.