Morphological changes of BTDA/m‐PDA polyimide banded spherulites: The effect of solvent on banding

BTDA/m‐PDA polyimide banded spherulites with different band spacing were observed in the same sandwiched film. Atom force microscopy (AFM) analysis suggested that the banded structure was caused by periodic twisting of radial grown lamella bundles. Based on polarizing light microscopy (PLM) and AFM observation, it was found that spherulites grown near the center of the film exhibited bigger band spacing and consisted of wider lamellae compared with those grown near the fringe, which was suggested to be caused by different solvent amount during imidization and crystallization: the more solvent existed, the wider the lamella would grow and the bigger the band spacing would be. It was further proved by changing the film thickness and PAA solution concentration. SEM observation showed that when crystallized in the solution, the lamella became ultra thick and straight, and formed small particles. Powder X‐ray diffraction revealed that crystal structures of the banded spherulite and the small particle were identical or at least very similar. Another solvent with lower boiling point was used in sample preparation, however, under the same preparation conditions, the grown features of banded spherulites did not change. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 659–667, 2008     

Anisotropic molecular structure in dip-coated films of linear poly(ethylene imine) studied by infrared multiple-angle incidence resolution spectrometry

Molecular structure in dip-coated films of linear poly(ethylene imine) (LPEI) on a germanium (Ge) substrate in dried and hydrated conditions have been analyzed by infrared multiple-angle incidence resolution spectrometry (IR MAIRS). The MAIRS-IP (in-plane) and -OP (out-of-plane) spectra of the dried film exhibited largely different patterns from each other, which indicated that LPEI molecules had an apparent molecular orientation with respect to the substrate surface. Although the film exhibited no peak in X-ray diffraction patterns, the low-crystallinity film has been found to have highly oriented molecular structure. Many key bands indicated that the molecules were involved in the double-stranded helix structure, which is specific to the anhydrate crystal of LPEI, with nearly perpendicular orientation. The Davydov splitting of the NH stretching vibration mode was readily captured by the IR MAIRS spectra, which also supported the helix standing model. When the film was stored in a humid condition, on the other hand, IR MAIRS spectra revealed that the helix was resolved to be straight chains, but the perpendicular orientation was kept unchanged. In addition, the MAIRS spectra also revealed molecular orientation of the water molecules of crystallization. The unique molecular arrangements are understandable by considering that the stabilization energy in the polymer monolayer directly attached on the substrate surface is minimized by the standing-molecule arrangements.     

Preparation of Oriented Liquid‐Crystalline/Isotropic Block Copolymer Films with Parallel or Perpendicular Arrangement of Smectic Layers and Lamellar Microdomains

Films of a symmetric liquid‐crystalline/isotropic block copolymer consisting of a smectic LC side‐chain polymer and polystyrene were prepared by solvent casting from solution and from the isotropic melt. By annealing the solvent‐cast film in the S_A phase an oriented microphase‐separated film of lamellar morphology was obtained in which both the lamellae of the block copolymer and the smectic layers of the LC block were oriented parallel to the film surface. A lamellar morphology with perpendicular orientation of lamellae and smectic layers was generated by cooling the block copolymer from the melt.     

Classification of semiconducting polymeric mesophases to optimize device postprocessing

Semiconducting polymers form a variety of phases and mesophases that respond differently to postdeposition solvent or thermal treatments. Here it is shown that classification of these materials into their appropriate mesophases can be a useful tool to optimize their thermal postdeposition treatments. Calorimetry is used to quantify differences between materials having similar molecular structures, using a well‐established framework based on the kinetics and thermodynamics of phase changes. By way of example, this classification scheme is used to identify differences in three polymers, poly(3‐hexylthiophene‐2,5‐diyl) and two isomeric bithiophene–thienothiophene copolymers. It is demonstrated that poly(3‐hexylthiophene) is a “normal” polymer crystal and that the two bithiophene–thienothiophene copolymers have liquid crystalline phases. The different phase structure is notable in light of the molecular similarity of the three polymers and has an impact on the thermal postprocessing conditions that maximize field effect charge carrier mobility in thin film transistor devices. Strong superheating effects are demonstrated for the two bithiophene–thienothiophene copolymers and the impact on annealing is demonstrated using grazing incidence X‐ray diffraction. Some suggestions are also put forth for what post‐processing should be employed for each class of polymer. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 1641–1653     

n-Type D-A Conjugated Polymers: Relationship Between Microstructure and Electrical/Mechanical Performance

Conjugated polymers are widely applied in optoelectronic devices due to their excellent optoelectronic properties, solution processibility, and intrinsic flexibility. High-performance films could be achieved with joint efforts from both molecular structure and film solid microstructure. Herein, research progress of the relationship between microstructure and electrical/mechanical performance of poly{[N,N'-bis(2-octyldodecyl)-representative of n-type donor-acceptor conjugated polymers, is reviewed. Its strong aggregation in solution is underlined and the methods to tune the degree of aggregation, such as solvent quality, molecular weight, and regioregularity, are compared. A liquid-crystalline behavior is evidenced in highly concentrated solutions during film drying, which favors the formation of highly anisotropic structures. Moreover, alignment techniques and thermal annealing are used to regulate molecular orientation and polymorphism in films. These structure characteristics offer great potential for researchers to handle film performances. Up to now, more attention has been paid to optimize the electrical performance of the devices. Achieving high-performance n-type conjugated polymer films with both superior mechanical and electrical properties is a newly emerging focus.     

In situ film characterization of thermally treated microstructured conducting polymer films

Based on a low‐cost fabrication routine microstructured conducting polymer films of poly (dioctylfluorene‐co‐benzothiadiazole) (F8BT) are prepared without any heat treatment or vacuum steps. The influence of thermal annealing at temperatures below the glass transition temperature of F8BT on such microstructured channel structures is investigated. In the applied structuring routine, a F8BT film is spin coated on a channel‐type hard master structure and afterwards floated on a flat support. Thereby, the properties of the final polymeric structures, for example channel width and height, can be tuned by simply varying the polymer concentration in solution and using the same master structure. With in situ grazing incidence small angle X‐ray scattering and imaging ellipsometry the installed channel structure and the influence of thermal treatment are probed. A complex interplay between a macroscopic polymer flow (reduced channel heights) and a molecular rearrangement (formation of mesoscopic crystallites) takes place during thermal annealing. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Molecular orientation of a ZnS‐nanocrystal‐modified M13 virus on a silicon substrate

The surface structure and cast film formation process of a ZnS‐nanocrystal‐modified M13 bacteriophage (ZnS–M13) were investigated. A ZnS–M13 film oriented under the influence of a capillary force was obtained on both single‐crystal and polycrystalline substrates. The film formation process was investigated with atomic force microscopy and scanning electron microscopy. The surface images showed that the degree of orientation of the molecular long axes greatly depended on the direction of force and the concentration of aqueous solutions. Controlling the aqueous solution concentration yielded a highly oriented ZnS–M13 film on an indium tin oxide plate. The ability to control the orientation of virus‐based films may lead to new types of hybrid materials in which the components are organized on several length scales. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 629–635, 2004     

Solvent Vapor Annealing Upgraded Orderly Intermolecular Stacking and Crystallinity to Enhance Memory Device Performance

Molecular stacking and crystallinity in a film can effectively affect the charge‐carrier mobility of semiconductor materials and corresponding device performance. Currently, solvent vapor annealing (SVA), as an effective thin‐film optimization strategy, which can select the appropriate solvent according to the characteristics of the molecular structure to optimize the intermolecular orderly arrangement, is often adopted. Thus, a small conjugated molecule C₂₀‐ID(TPCN)₂ with flexible alkyl side chains was synthesized and applied as active layer of sandwich memory devices. The active layer film has been annealed with different polar solvent vapors to evaluate the relationship among the molecular structure, solvent selection, annealing parameters and intermolecular stacking. Compared to un‐annealed devices, the memory devices based on the films through CH₂Cl₂‐annealing show better performance with a lower threshold voltage due to developed ordered molecular aggregation and better crystallinity, while a hydrophilic solvent vapor will weaken the device performance. This work not only reveals that selecting an appropriate solvent vapor for the molecular structure could be of vital importance in inducing the desired intermolecular stacking mode, but also provides a novel insight for the realization of organic semiconductor devices with excellent performance.     

Influence of rapid thermal annealing on structure and interfacial characteristic of ZnO thin films

Highly C‐axis oriented ZnO thin film was manufactured by radio‐frequency magnetron sputtering technique on Si (111) substrate. The main objective was to study the influence of rapid thermal annealing (RTA) temperature on the structure and interfacial characteristic of ZnO thin films. X‐ray diffraction results showed that the ZnO thin films annealed at 600 °C by RTA technique had a perfect C‐axis preferred orientation compared to the other ZnO thin films, and the full width at half maximum of ZnO (002) rocking curve measurements indicted that the RTA‐annealed ZnO thin films possessed better crystal structure. Atom force microscopy displayed that the grain size of RTA‐annealed ZnO thin films was fine and uniform compared with the as‐deposited ZnO thin films, although the grains grew in RTA process and the root meant square roughness was smaller than that of as‐deposited films. High‐resolution transmission electron microscopy showed that there was an obvious amorphous layer between ZnO thin films and Si substrate, but the RTA‐annealed ZnO thin films exhibited larger and denser columnar structure and a preferred orientation with highly c axis perpendicular to the amorphous layer. Copyright © 2012 John Wiley & Sons, Ltd.     

Uniaxial alignment of poly(3-hexylthiophene) nanofibers by zone-casting approach

The preparation of large area coverage of films with uniaxially aligned poly(3-hexylthiophene)(P3HT) nanofibers by using zone-casting approach is reported.The length and the orientation of the nanofibers are defined by the solubility of the solvent,the P3HT molecular weight and the substrate temperature.The length of the oriented nanofibers could be increased from 1 μm to more than 10 μm by adding poor solvent into the P3HT solution.It is found that for P3HT of relatively low molecular weight,a solvent with relatively low solubility has to be chosen to get the oriented film.While for the high molecular weight P3HT,the solvent with a relatively high solubility has to be used.The well-aligned film could be obtained because of the solute concentration gradient in the region where the critical concentration is reached during the zone-casting process.Particularly,the solvent evaporation rate and crystallization rate must be chosen properly to satisfy the stationary conditions above,which were controlled by an appropriate choice of solvent and substrate temperature.The film prepared by zone-casting approach had microcrystalline P3HT domains with more inter-chain order than spin-coating film.Meanwhile,the P3HT π-π stacking direction was parallel to the alignment direction of the nanofibers.     

Fabrication of microporous membranes from melt extruded polypropylene precursor films via stretching: Effect of annealing

In this work, the effects of annealing conditions on the microstructure of polypropylene(PP) precursor films and further on the porous structure and permeability of stretched membranes were investigated. Combinations of WAXD, FTIR, DSC and DMA results clearly showed the crystalline orientation and crystallinity of the precursor film increased with annealing temperature, while the molecular chain entanglements in the amorphous phase decreased. Changes in the deformation behavior suggested more lamellar separation occurred for the films annealed at higher temperatures. Surface morphologies of the membranes examined by SEM revealed more pore number and uniform porous structure as the annealing temperature increased. In accordance with the SEM results, the permeability of the membranes increased with annealing temperature. On the other hand, it was found that 10 min was almost enough for the annealing process to obtain the microporous membranes with an optimal permeability.     

Synergistic Effects of External Electric Field and Solvent Vapor Annealing with Different Polarities to Enhance β-Phase and Carrier Mobility of the Poly(9,9-dioctylfluorene) Films

In this work, the synergistic effects of external electric field(EEF) and solvent vapor annealing to enhance β-phase and carrier mobility of poly(9,9-dioctylfluorene)(PFO) films were investigated. It is found that EEF can promote the PFO β-phase conformation transition and orientate the PFO chains along the EEF direction with the assistance of polar solvent vapor annealing. PFO chain orderness is closely related to the solvent polarity. In particular, the β-phase content in the annealed film of strong polar chloroform vapor increases from 18.7% to 34.9% after EEF treatment. Meanwhile a characteristic needle-like crystal is formed in the film, as a result, the hole mobility is enhanced by an order of magnitude. The mechanism can be attributed to the fast polarization of solvent dipole under the action of EEF, thus forming a driving force that greatly facilitates the orientation of PFO dipole unit. Research also reveals that EEF driving of the PFO chains does not occur with an insoluble solvent vapor since the solvent molecules cannot swell the film, thus there is insufficient free volume for PFO chains to adjust their conformation. This research enriches the understanding of the relationship between solvent vapor annealing and EEF in orientation polymers, and this method is simple and controlled, and capable of integrating into large-area thin film process, which provides new insights to manufacture low-cost and highly ordered polymer films, and is of great significance to enhance carrier mobility and efficiency of photoelectric devices based on polymer condensed matter physics.     

Structural and compositional effects on thermal expansion behavior in polyimide substrates of varying thicknesses

Polyimide films with thicknesses ranging from 6 μm to 80 μm were prepared with a solvent casting method to explore film thickness effects on the in-plane thermal expansion coefficient (CTE). In the case of polyimide films composed of bulky and flexible molecular units, CTE is consistent regardless of film thickness. In contrast, films with rigid and planar molecular structure show CTE increase according to the increase of film thickness up to 40–50 μm, which then plateau for thicker films. It is apparent that the film thickness dependent thermal expansion originates from complex effects of molecular orientation, charge transfer complex formation, and crystal formation as a function of film thicknesses, through characterization on UV–Vis absorption, crystalline structure, glass transition behavior, and optical retardation. These results provide insight into the design of polymer structures for flexible display substrates that require appropriate CTE values.     

Morphology and mechanical properties of blown films of a low‐density polyethylene/linear low‐density polyethylene blend

The morphologies of films blown from a low‐density polyethylene (LDPE), a linear low‐density polyethylene (LLDPE), and their blend have been characterized and compared using transmission electron microscopy, small‐angle X‐ray scattering, infrared dichroism, and thermal shrinkage techniques. The blending has a significant effect on film morphology. Under similar processing conditions, the LLDPE film has a relatively random crystal orientation. The film made from the LDPE/LLDPE blend possesses the highest degree of crystal orientation. However, the LDPE film has the greatest amorphous phase orientation. A mechanism is proposed to account for this unusual phenomenon. Cocrystallization between LDPE and LLDPE occurs in the blowing process of the LDPE and LLDPE blend. The structure–property relationship is also discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 507–518, 2002; DOI 10.1002/polb.10115     

热处理对尼龙6及其与聚酰胺嵌段共聚物共混体系晶体熔融行为和结晶结构的影响

采用溶液共混-共沉淀的办法获得尼龙6及聚酰胺嵌段共聚物/尼龙6共混体系粉末,样品在260℃下熔融之后经程序降温的方法得到非淬火样品,然后分别在190℃下高温退火不同时间(0~48 h),采用示差扫描量热仪(DSC)、广角X射线衍射仪(WAXD)、偏光显微镜(POM)等表征手段研究热处理对体系晶体熔融行为和结晶结构的影响.结果表明,(1)在相同的热历史条件下,嵌段共聚物的存在影响了尼龙6的结晶行为及结晶结构;(2)退火处理对两种样品有着不同的影响,对于尼龙6体系,退火处理促进了非晶相向晶相的转变,大大提高样品的结晶完善程度和结晶度;对于共混体系,退火处理同样促进了非晶相向晶相的转变,同时形成新的α型和γ型结晶,体系的结晶完善程度明显提高,退火48 h后,结晶度比原始样品提高约84%.     

Effect of solvent annealing on the tensile deformation mechanism of a colloidal crystalline polymeric latex film

The influence of solvent annealing on microscopic deformational behavior of a styrene/n-butyl acrylate copolymer latex film subjected to uniaxial tensile deformation was studied by small-angle X-ray scattering. It was demonstrated that the microscopic deformation mechanism of the latex films transformed from a nonaffine deformation behavior to an affine deformation behavior after solvent annealing. This was attributed to the interdiffusion of polymeric chains between adjacent swollen latex particles in the film. It turns out that solvent annealing is much more efficient than thermal annealing due to a much slow evaporation process after solvent annealing.     

Photoalignmentability of silsesquioxane-containing citraconimide and its solvent-induced surface enrichment in PMMA matrix

Photo-reactive polymer of silsesquioxane-containing citraconimide (SQ-CI) was synthesised and evaluated as a photoalignment layer for polymerisable liquid crystals (PLC). A generation mechanism of the anisotropy by the linearly polarised ultraviolet light was discussed by comparing optical retardation of SQ-CI with theoretical calculations using density functional theory. In addition, the SQ-CI and poly(methyl methacrylate) were blended for a model of unification of photoalignment layer and protection layer in liquid crystal display. The orientation of PLC on the blend film was dominated by the solvent used for the sample preparation of PMMA/SQ-CI blend. We found that the SQ-CI was enriched at surface of the blend film prepared from the ?-butyrolactone solution, while not in the case of the film prepared from cyclopentanone solution. The surface enrichment in the film prepared from ?-butyrolactone solution does not follow the conventional mechanism which is that the lower surface free energy component segregates to the blend surface, because the surface free energy of SQ-CI is higher than that of PMMA. Based on the result of solvent-annealing effect and photoalignmentability, we concluded that the mechanism of surface enrichment was explained due to the difference of affinity between the polymer and the solvent.     

A Soluble Dynamic Complex Strategy for the Solution‐Processed Fabrication of Organic Thin‐Film Transistors of a Boron‐Containing Polycyclic Aromatic Hydrocarbon

The solution‐processed fabrication of thin films of organic semiconductors enables the production of cost‐effective, large‐area organic electronic devices under mild conditions. The formation/dissociation of a dynamic B?N coordination bond can be used for the solution‐processed fabrication of semiconducting films of polycyclic aromatic hydrocarbon (PAH) materials. The poor solubility of a boron‐containing PAH in chloroform, toluene, and chlorobenzene was significantly improved by addition of minor amounts (1 wt % of solvent) of pyridine derivatives, as their coordination to the boron atom suppresses the inherent propensity of the PAHs to form π‐stacks. Spin‐coating solutions of the thus formed Lewis acid–base complexes resulted in the formation of amorphous thin films, which could be converted into polycrystalline films of the boron‐containing PAH upon thermal annealing. Organic thin‐film transistors prepared by this solution process displayed typical p‐type characteristics.     

聚苯醚/聚苯乙烯共混物溶液浇铸膜的热演化行为

聚苯醚与聚苯乙烯共混物是目前相容性最好的共混体系之一。几十年来人们对该共混体系相容的原因进行了广泛的研究^[1-4]。聚苯醚是半结晶聚合物,在溶剂或溶剂蒸气存在的条件下容易形成结晶,溶剂的性质及结晶的条件都会影响聚苯醚的结晶结构及其形态^[5-8]。用溶液共昆、凝聚成膜的方法制备共混物时,一种结晶性高分子怎样与另一种高分子演化成相容的非晶共混体系,是一个比较有意义的研究课题。本文运用DSC方法,研究了聚苯醚与聚苯乙烯两者溶液共混凝聚成膜后,在各种热历史条件下结晶结构的消亡和演化成非晶相容体系的行为。     

Thermal and Photochemical Control of Molecular Orientation of Azo‐Functionalized Polymer Liquid Crystals and Application for Photo‐Rewritable Paper

A photo‐responsive multi‐bilayered film consisting of azobenzene polymer liquid crystals (PA6Az1) and poly(vinyl alcohol) (PVA) has been prepared on a glass substrate by alternate spin coating of the polymer solutions. The reflectivity of the multi‐bilayered film disappears by annealing at 80 °C. The disappearance of the reflection by the annealing is related to the thermal out‐of‐plane molecular orientation of PA6Az1 even in the multi‐bilayered film, which leads to a very small difference in refractive indices between PA6Az1 and PVA. The reflectance of the multi‐bilayered film is increased again by UV irradiation because of the transformation from the out‐of‐plane orientation to an in‐plane random orientation. In this way, on–off switching of the reflection is achieved by combination of the thermally spontaneous out‐of‐plane molecular orientation and following photoisomerization of PA6Az1 comprising the multi‐bilayered film.