Changes In Crystalline Morphology Research Articles

Influence of polyether ether ketone (PEEK) viscosity on interlayer shear strength in screw extrusion additive manufacturing

The excellent properties of polyether ether ketone (PEEK) have made it applicable for high-performance components in aerospace, electrical, chemical, and biomedical industries. Material extrusion (MEX) additive manufacturing (AM) of PEEK using fused filament fabrication (FFF) predominantly uses modified PEEK filament. Fused granulate fabrication (FGF) systems conventionally employ injection moulding and extrusion grades which are not specifically formulated for MEX AM. There is a limited amount of research on the use of these grades for MEX AM using PEEK. This study evaluated different viscosity PEEK grades at various extruder temperatures to optimise interlayer strength and therefore determine the best grades of PEEK for FGF. Compression shear testing (CST) was used to study this property as it represents a mostly shear loading condition i.e., without bending, compared to other conventional shear testing methods, whilst also being easier to fabricate. PEEK crystallinity is corelated to the interlayer strength and was evaluated using differential scanning calorimetry (DSC), Raman spectroscopy and X-ray diffraction (XRD). The highest interlayer strength of 17.70±0.58 MPa and the lowest crystallisation degree of 29.7±1.3% (Raman) was achieved by VESTAKEEP L4000G PEEK, printed at the highest extruder temperature (420°C). This grade had the highest viscosity or the lowest melt volume-flow rate (MVR). In contrast with lower MVR grades, the high MVR grade VESTAKEEP L2000G, achieved a higher increase in bond strength and crystallinity with higher extruder temperatures. At lower MVR, the crystallinity was found to decrease from 33% to 30% with increasing extruder temperatures, along with an increase in melting temperature. This behaviour was attributed to a change in crystalline morphology possibly caused by the long residence time and high processing temperature of FGF.

Evolution of the Deformation‐ and Flow‐Induced Crystallization and Characterization of the Microstructure of a Single Spherulite, Lamella, and Chain of Isotactic Polypropylene

AbstractIsotactic polypropylene (iPP) is a frequently used polymer in industrial processing and scientific research, used as a model material. This review highlights some current and forefront issues in polymer science and engineering. This review alludes to classical deformation schemes to interpret the complicated deformation in isotactic polypropylene as a semicrystalline polymer. Also, due to the complex hierarchical structures of crystallized polymers, the progress on the multiscale and multistage microstructural evolution covering each deformation stage from the initiation of plasticity until failure is mainly concerned, particularly in terms of crystalline morphology changes. Specifically, the characterization of the microstructure evolution of a single spherulite, lamella, and chain of isotactic polypropylene will be emphasized and mentioned. Here, the authors are most interested in the results obtained from stretching (strain‐induced) orientation and crystallization studies accompanied by the in situ scattering and spectroscopy techniques offering a detection window from nano to micrometer scale, which should be able to reflect the microstructural changes at different length scales of interest. During polymer processing, the melts are frequently subjected to shear or/and elongation flow fields, producing flow‐induced molecular chain orientation in the melt. The oriented molecular chains crystallize differently than those encountered under quiescent conditions. Thus, orientation‐induced crystallization has long been an object of intense interest. A vast body of research is reported about the effects of preorientation on the crystallization of various polymers. Among them, iPP is most frequently studied since its diversified structure and morphology are very sensitive to changes in processing conditions and molecular parameters.

Revisiting stress-oscillation in cold drawing of poly(ethylene terephthalate)

This paper investigates the unusual phenomenon of stress-oscillation (SO) where a polymer exhibits periodic oscillatory neck propagation during drawing. It has been suggested that heat generation at the neck is critical, while other theories propose that an unstable neck stress is the controlling mechanism. Here, we study cold-drawing of poly(ethylene terephthalate) at 100 mm min−1 where SO has been monitored by thermal analysis. The morphology of the transparent and opaque bands were investigated using DSC, X-ray scattering and microscopy. It is revealed that heat release is a consequence of the plastic deformation as opposed to being the cause of the yielding. Neck geometry plays a key role in the mechanism. Temperature rise at the neck is low (9 °C) and does not lead to a change in crystalline morphology between the transparent and opaque bands. It is concluded that stress-induced crystallization plays no role in the SO process for cold drawn PET and that the opaque bands result from axial voiding during high strain-rate yielding.

Consequences of Radiothermal Ageing on the Crystalline Morphology of Additive-Free Silane-Crosslinked Polyethylene.

The radiothermal ageing of silane-crosslinked low-density PE (Si-XLPE) films was studied in the air under three different dose rates (8.5, 77.8, and 400 Gy·h−1) at a low temperature close to ambient (47, 47, and 21 °C, respectively). Changes in crystalline morphology were investigated using a multi-technique approach based on differential scanning calorimetry (DSC), wide- (WAXS) and small-angle X-ray scattering (SAXS), and density measurements. In particular, the changes in four structural variables were accurately monitored during radiothermal ageing: crystallinity ratio (), crystalline lamellae thickness (), long period (), and interlamellar spacing (). Concerning the changes in , a perfect agreement was found between DSC and WAXS experiments. Successive sequences of self-nucleation and annealing (SSA) were also performed on aged Si-XLPE samples in the DSC chamber in order to assess the thickness distribution of crystalline lamellae. This method allowed the thermally splitting of the melting domain of Si-XLPE into a series of elementary melting peaks, with each one characterised by a distinct thickness of crystalline lamellae. DSC (used with the SSA method) showed a slight increase in during the oxidation of Si-XLPE, while SAXS confirmed a catastrophic decrease in . The critical value of the interlamellar spacing characterising the ductile/brittle transition of Si-XLPE was found to be of the same order of magnitude as that for linear polyethylene ( nm). This structural end-of-life criterion can now be used for predicting the lifetime of Si-XLPE in a nuclear environment.

The effect of the melt-drawing ratio on the microstructure and mechanical properties of poly(butylene succinate) cast films with row-nucleated lamellar structure

High-performance PBS films can be prepared by the melt-stretching method. The effect of the melt-drawing ratio (MDR) on the mechanical properties and microstructure of PBS cast films prepared by melt-stretching is studied in this paper. The elastic modulus, tensile stress, and strain hardening increase with increasing MDR. With an MDR of 25–50, the crystalline morphology changes from deformed spherulites to row-nucleated lamellar structure. The lateral size and orientation of the lamellae apparently improve with the MDR. When the MDR is within 50–125, the row-nucleated lamellar structure improves slightly by increasing the lateral size and orientation of the lamellae. The component fraction and thickness of the mobile (MAF) and rigid (RAF) amorphous fractions and crystalline phase are nearly unchanged within the whole MDR range. The increases in lateral size and orientation improve the mechanical properties of the films. Significantly, the linear relationship between the elastic modulus and orientation at MDRs from 50 to 125 indicates that the elastic modulus is determined by the crystal orientation in PBS cast films with row-nucleated lamellae. This work evaluates the importance of orientation for microstructure and properties of PBS films, which may guide the processing of high-performance PBS films.

Celecoxib Crystallized from Hydrophilic Polymeric Solutions Showed Modified Crystalline Behavior with an Improved Dissolution Profile

The crystallization technique has been established as a cost-effective and simple approach to improve the dissolution rate and oral bioavailability of poorly soluble drugs. This study was carried out to study the effect of some selected hydrophilic polymers such as methyl cellulose, hydroxypropyl methylcellulose (HPMC), polyvinyl alcohol, and carboxymethyl cellulose on the crystal behavior and dissolution properties of celecoxib (CLX), a common nonsteroidal anti-inflammatory drug. Structural and spectral characteristics of crystallized CLX have been studied by Fourier transform infrared (FTIR) spectroscopy, diffraction scanning calorimetry (DSC), and X-ray diffraction (XRD) analysis. From FTIR and DSC analysis, no significant shifting of peaks or appearance of any new peaks (for polymers) were observed, which indicated the absence of any major interaction between drug and polymers as well as the absence of polymers in the final crystallized product of CLX. The XRD analysis showed a change in crystalline morphology to some extent. The dissolution rate of crystallized CLX in the presence of polymers (particularly with HPMC) was significantly improved compared with plain CLX. The improved dissolution profile of the experimental CLX crystal products could be an indication of improved bioavailability of CLX for better clinical outcome.

Subtle changes of the crystalline lens after cycloplegia: a retrospective study

BackgroundThe purpose of this study was to evaluate the shape of the crystalline lens in terms of biometry and diopters before and after cycloplegia using the CASIA2 swept-source (SS) optical coherence tomography (OCT) system on the anterior segment.MethodsThis was a retrospective study. Children and adolescents (26 males and 29 females, aged 4–21 years) with simple ametropia were selected for optometry and CASIA2 imaging at 2 separate visits before and after cycloplegia. Diopter values were derived from the spherical power (S) obtained by optometry. Biometric parameters of the crystalline lens, including the anterior chamber depth (ACD), anterior and posterior curvature of the lens (ACL and PCL), lens thickness (LTH), lens decentration (LD), lens tilt (LT), and equivalent diameter of the lens (LED), were measured by the CASIA2 system. The differences in these parameters after compared with before cycloplegia were determined, and their relationships were analyzed.ResultsFifty-five participants (106 eyes) were initially enrolled. There was a significant difference (P < 0.05) in the S (t=-7.026, P < 0.001), ACD (t=-8.796, P < 0.001), ACL (t=-13.263, P < 0.001) and LTH (t = 7.363, P < 0.001) after compared with before cycloplegia. The change in the PCL (t = 1.557, P = 0.122), LD (t = 0.876, P = 0.383), LT (t = 0.440, P = 0.661) and LED (t=-0.351, P = 0.726) was not statistically significant (P > 0.05). There was a significant (P < 0.05) correlation of the change in the S with that in the ACL (r = 0.466, P < 0.001), LTH (r=-0.592, P < 0.001), and LED (r = 0.223, P = 0.021) but not the PCL (r = 0.19, P = 0.051), LD (r=-0.048, P = 0.0628) or LT (r=-0.022, P = 0.822). Furthermore, the change in the ACD was closely related to the change in crystalline morphology. However, in children and adolescents, we found that the change in crystalline morphology was unrelated to age.ConclusionsChanges in lens morphology after compared with before cycloplegia are mainly related to the ACL and LTH, but there is no difference in the PCL, LD, LT, or LED. In the adolescent population, change in the S is related to change in the ACL, LED and LTH. However, age is unrelated to the shape and tendency of the crystalline lens. Further research is required to determine whether the same conclusion applies to different age groups and different refractive states (myopia, hyperopia, emmetropia) .

Structural and Barrier Properties of Compatibilized PE/PA6 Multinanolayer Films.

The barrier performance and structural lightening of organic materials are increasingly desired and constitute a major challenge for manufacturers, particularly for transport and packaging. A promising technique which tends to emerge in recent years is that of multinanolayer coextrusion. The advantage is that it can produce multilayers made of thousands of very thin layers, leading to new properties due to crystalline morphology changes induced by confinement. This paper is focusing on the study of multinanolayered films with alternated polyethylene (PE), compatibilizer (PEgMA) and polyamide 6 (PA6) layers and made by a forced assembly coextrusion process equipped with layer multiplying elements (LME). PE/PA6 multilayer films consisting of 5 to 2049 layers (respectively 0 to 9 LME) were successfully obtained with well-organized multilayered structure. The evolution of the morphology and the microstructure of these two semi-crystalline polymers, when the thickness of each polymer layer decreases from micro-scale to nano-scale, was correlated to the water and gas transport properties of the PE/PA multilayers. The expected improvement of barrier properties was limited due to the on-edge orientation of crystals in very thin PE and PA6 layers. Despite this change of crystalline morphology, a slight improvement of the gas barrier properties was shown by comparing experimental results with permeabilities predicted on the basis of a serial model developed by considering a PE/PA6 interphase. This interphase observed by TEM images and the on-edge crystal orientation in multilayers were evidenced from mechanical properties showing an increase of the stiffness and the strength.

Thermal aging of High Tenacity Polyvinyl Alcohol yarns

A both multiscale and multi-techniques approach was developed to characterize the thermal aging in air at 70, 90, 100 and 120 °C of High Tenacity Polyvinyl Alcohol (HT-PVAl) yarns, and to elucidate the consequences of thermal aging on the chemical structure, crystalline morphology and several physico-chemical and mechanical properties of practical interest. First of all, FTIR and UV–Vis spectrometries showed that the main degradation products are isolated (1656 cm−1) and conjugated (1592 cm−1) carbon-carbon double bonds, and a large variety of carbonyl products such as: esters (1757 cm−1), aldehydes (1737 cm−1), carboxylic acids (1720 cm−1), ketones (1707 cm−1), but also polyenones (1630 cm−1). Possible mechanistic schemes were then proposed to explain the formation of all these different degradation products. Moreover, no change in the physico-chemical properties of the amorphous phase was detected by modulated differential scanning calorimetry and dynamic vapor sorption. In contrast, the decrease in both melting temperature and crystallinity ratio with exposure time clearly indicates a “nibbling” of the crystalline phase during thermal aging, thus highlighting a chemical attack preferentially localized at the amorphous/crystal interface for this complex anisotropic material. This heterogeneous degradation is responsible for the loss of fracture properties in tension of HT-PVAl yarns. Fairly simple relationships between the structural variables determined at the different scales of analysis were established. As an example, a linear correlation was found between the changes in fracture properties and the changes in crystalline morphology.

Formation of Asymmetric Leaf-Shaped Crystals in Ultrathin Films of Oriented Polyethylene Molecules Resulting from High-Temperature Relaxation and Recrystallization

We melted, annealed, and recrystallized ultrathin films of oriented polyethylene (PE) molecules prepared by melt-drawing. A large number of randomly oriented asymmetric leaf-shaped crystalline structures consisting of preferentially oriented lamellae were formed simultaneously, as observed by optical and atomic force microscopies. The structural arrangement within these leaf-shaped crystalline structures was identified by grazing incidence X-ray diffraction. These structures consisted of two distinct sections, both differing strongly from circular spherulites obtained by crystalizing an isotropic melt. Besides, regions containing groups of stacks of slightly inclined but well-aligned flat-on lamellae and regions of less orderly arranged edge-on lamellae were found. When increasing the annealing temperature and/or annealing time, a change in morphology from the leaf-shaped crystalline structures to spherulites with two symmetric “eyes” was observed. Intriguingly, the annealing times required for such a change in crystalline morphology were about four orders of magnitude longer than the longest bulk relaxation time (reptation time). Because the appearance of spherulites indicates that films became equilibrated and reached a state of an isotropic melt before recrystallization, we may conclude that oriented PE chains in ultrathin films possessed a long-term memory of the preparation-induced chain stretching. Considering that the morphology and relaxation kinetics of PE films depended appreciably on the substrate properties and film thickness, we conclude that the formation of asymmetric leaf-shaped crystalline structures was also affected by the interaction of PE chains with the substrate and spatial confinement. The present results may shed new light on slow relaxation and reorganization processes encountered when long-chain polymers became oriented during sample processing.

Toward uniform pore-size distribution and high porosity of isotactic polypropylene microporous membrane by adding a small amount of ultrafine full-vulcanized powder rubber

Lots of works have been done on the pore formation of β nucleated PP membranes during stretching, and most of these works focus on the effects of crystal form and processing conditions on the performance of PP membrane. In our work, the crystalline morphology of β crystal was modulated by adding a small amount of ultrafine full-vulcanized powder rubber (EA-UFPR), and subsequently, the influence of crystalline morphology on pore-size distribution and porosity was investigated. It was interesting to find that the crystalline morphology changes from spherulites into large quantity of β-transcrystals (β-TCs) by adding EA-UFPR. The related transformation mechanism was investigated by polarized optical microscope (POM), differential scanning calorimetry (DSC) and rheological tests. It was found that the fibrils of β nucleating agent could be directly absorbed on the surface of EA-UFPR particles due to the possible hydrogen-bond interaction between them as evidenced by FTIR, which hindering the self-assembly of these fibrils into big framework. As a result, the tiny fibrils with fine dispersion induce the formation of β-TC networks instead of isolated spherulites. Furthermore, the membrane with uniformly distributed pores and high porosity can be achieved from the samples with β-TC networks. This is possibly related to their loosely-packed lamella and de-bonding of EA-UFPR particles during microvoids formation. This work provides a convenient and reliable strategy for the preparation of PP microporous membranes with high performance.

Improvement of the impact strength of ethylene‐propylene random copolymers by nucleation

ABSTRACTFive ethylene‐propylene random copolymers were nucleated with two soluble nucleating agents. Ethylene content changed between 1.7 and 5.3 wt %, while nucleating agent content was adjusted according to the solubility of the additive. It changed from 0 to 5000 ppm for the sorbitol (1,2,3‐tridesoxy‐4,6:5,7‐bis‐O‐[(4‐propylphenyl) methylene]‐nonitol) and from 0 to 500 ppm for the trisamide compound (1,3,5‐benzene‐trisamide) used. Crystalline structure was analyzed in detail by various methods (DSC, XRD, and SEM). Mechanical properties were characterized by tensile and instrumented impact measurements. The results showed that most properties changed moderately upon nucleation, but impact resistance increased considerably. Spherulitic structure was not detected, but instead in the presence of the soluble nucleating agents used a microcrystalline structure formed. The large increase of impact resistance could not be related directly to changes in crystalline morphology. On the other hand, local rearrangement of morphology was detected by XRD and SEM analysis including an increase of lamella thickness, crystal orientation, and the formation of shish‐kebab structures in the core of the injection molded specimens. A small increase in the γ‐phase content of PP was also observed. These changes increased crack propagation energy considerably leading to the large improvement observed in impact resistance. Although the phenomenon could be related to ethylene content, differences in molecular weight also helped to explain the changes observed. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 43823.

Influence of film thickness on the crystalline morphology of a copolyesterurethane comprising crystallizable poly(ɛ-caprolactone) soft segments.

In this work, a model approach to investigate changes in crystalline morphology during heating/cooling procedures in the context of programming and induction of the shape-memory effect is presented. Atomic-force microscopy (AFM) was performed to investigate the variations in poly(ɛ-caprolactone) (PCL) crystalline morphology in nm thin films on a silicon substrate and a film with 20 μm thickness, prepared from a copolyesterurethane (named PDLCL) consisting of crystallizable poly(ω-pentadecalactone) (PPDL) hard segments and crystallizable PCL segments forming switching domains. PCL crystals in switching domains melted/recrystallized repeatedly during heating/cooling cycles between 20 and 70 °C, while no evident variation in PPDL crystals forming hard domains was observed. When film thickness was 20 nm, PCL edge-on lamellae were observed, confined in the phase-separated morphology. Flat-on PCL lamellae, which broke out from the previous phase-separated morphology, were obtained at a film thickness of 170 nm. In contrast, large PCL spherulites were observed in the 20 μm thick film. PCL crystalline morphology in PDLCL as well as the competition between crystallization and phase separation can be tailored by the film thickness and the substrate. Such AFM investigations on thin films can be a helpful approach for predicting the crystal morphology in micro-/nanoscaled objects.

Effect of morphology on electrical treeing in low density polyethylene nanocomposites

Influence of polymer morphology on the inception and the growth of electrical trees in unfilled low density polyethylene (LDPE) as well as LDPE filled with 1, 3 and 5% by weight nanoalumina samples stressed with 50 Hz ac voltage has been studied. It is seen that there is a significant improvement in tree inception voltage with filler loading in LDPE filled with nanoparticles. Tree inception voltage increased with the filler loading up to 3% by weight nanoalumina loading and showed a reduction at 5% by weight loading. Change in tree growth patterns from branch to bush as well as a slower tree growth with increase in filler loading in LDPE alumina nanocomposites were observed. The degree of crystallinity and change in crystalline morphology induced by the presence of alumina nanoparticles in LDPE was studied using differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). DSC results show a similar melting behaviour for both unfilled LDPE and LDPE nanocomposites. However, there is a reduction in the degree of crystallinity for LDPE filled with 5% by weight nanoalumina. An increase in lamellae packing with increase in filler loadings and a highly disordered spherulitic structure for LDPE filled with 5% by weight nanoalumina was observed from the SEM images. The slow propagation of tree growth as well as reduction in tree inception voltage with increase in filler loadings were attributed to the morphological changes observed in the LDPE nanocomposites.

Monitoring nonisothermal crystallization of thermoplastic polymers using a quartz crystal resonator

A new monitoring device for the nonisothermal crystallization of thermoplastic polymers, polyethylene, polypropylene, polystyrene, and polyamide, is developed utilizing a quartz crystal resonator, and its performance is evaluated by comparing the measurements with the results of DSC thermoanalysis and microscopic observation. The experimental results of four different polymers indicate that the variation of resonant freency of the quartz crystal resonator is a good means to monitor the crystallization process. Though the measurements of melting and crystallization are close to the DSC outcome, more deviation is observed with the new device. The change in crystalline morphology during the crystallization process is also detected from the slope changes of the frequency decrease. In comparison with the microscopic observation of polymer films, it is found that the processes of nucleation and crystal growth in nonisothermal crystallization can be explained with the variation of the resonant frequency of the quartz crystal resonator. In addition, crystallization kinetics is modeled with the Avrami equation. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

A Study of Mechanisms of Poly (PhenyleneSulfide) Thermal Degradation in Air

Because of its special properties and commercial significance, Poly(phenylene sulfide) (PPS) has been the subject of many research efforts since its commercial introduction in 1967. Intensive work has been done on its crystalline structure and morphology and its thermal behaviour. But fewer investigations have been carried out to understand long term behaviour in high temperature environments. Always anticipating industrial needs linked to power integration, we have launched an extensive study on thermal aging in air of PPS at 250°C. This study has shown that PPS thermal degradation in air happens by intermolecular branching reaction, similar to crosslinking. This phenomenon was already known for temperature above 300°C. This crosslinking is evidenced by rheometry where the relative position of G’ and G’’ above melting temperature changes with aging. IR spectroscopy confirms that para substituted benzene in PPS molecule is transformed in 1,2,4 trisubstituted benzene. DSC measurements evidence both an elevation of melting temperature and a change in melting endotherm showing significant changes in crystalline morphology along aging, which tends to indicate that crosslinking occurs in crystalline phase. Then degradation implies drastic loss of mechanical properties leading to destruction of the sample.

Effect of confinement on the relaxation behavior of poly(ethylene oxide)

It is widely thought that confinement of an amorphous polymer alters the chain mobility, which affects the temperature and intensity of the glass transition. The present study sought to determine whether the same effects extend to semicrystalline polymers. Confinement was achieved by forced assembly of hundreds of alternating layers of poly(ethylene oxide) (PEO) with either poly(ethylene- co-acrylic acid) or polystyrene. The confinement gradually reduced the intensity of the PEO β-relaxation as the layer thickness decreased from the microscale to the nanoscale. By considering the changes in crystalline morphology that accompanied layer confinement, it was possible to completely account for the reduction in relaxation intensity using standard mechanical models. The viscoelastic behavior of the amorphous phase was satisfactorily represented by a modified standard linear solid (SLS). The amorphous and crystalline contributions were combined using a combination of parallel and series coupling in accordance with the Takayanagi model. No adjustment in the viscoelastic parameters of the modified SLS was required, indicating that there was no significant change in amorphous chain dynamics even in layers as thin as 45 nm.

Changes in crystalline morphology, thermal, and mechanical properties with hydrolytic degradation of immiscible biodegradable PPDX/PCL blends

AbstractImmiscible blends of high molecular weight commercial poly(p‐dioxanone) (PPDX) and poly(ε‐caprolactone) (PCL) were prepared by melt mixing in a wide composition range. The materials were exposed to a hydrolysis medium (phosphate buffer kept at a constant pH of 7.2) at 37°C during 36 weeks. The change in weight of the samples as well as their thermal properties, morphology, spherulitic crystallization kinetics, and tensile properties were studied as a function of degradation time. As PCL does not experience weight loss during the entire degradation period explored here, weight loss was indicative of PPDX degradation only. The combined results of calorimetry, spherulitic texture, and spherulite growth kinetics allowed us to establish that the PPDX component in the blends experiences a much faster degradation rate than in neat PPDX. Such increase in degradation rate could be due to the larger surface area of PPDX component when it is dispersed in immiscible PCL. Nevertheless, the presence of PCL in the blends can extend the physical integrity of the samples in the degradation medium as well as their mechanical properties for longer periods of time as compared with neat PPDX. Therefore, the blends may be good candidates for replacing neat PPDX in specific applications requiring longer life time of the material. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Work function and valence band structure of tin-doped indium oxide thin films for OLEDs

Transparent conducting ITO thin film has been widely used as anode material in OLEDs due to its good optical transparency, low electrical resistivity, ease of patterning, high work function and efficient hole injection properties. The interface between ITO and organic layer in OLED device is thus important and can influence the electrical and luminescent properties. In this report, ITO substrates were treated with 20% H 3PO 4 solution. The corresponding changes in crystalline morphology were studied by X-ray diffraction. X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS) were performed at ∼10 −9 Torr to study the work function and the valence band structure of ITO substrates. It was found that work function became slightly lower after the treatment, probably caused by the formation of metal complex compounds and metal hydroxides. The binding energy of In 3d 5/2 shifted from 444.6 to 445.3 eV. This shifting was referred to the formation of In–OH bonding. It would be easier to provide electron by In–OH bonding than by In–O–In or Sn–O–Sn when photons reached ITO surface. The interface between ITO and CuPc was improved through polar surface and less aggregation. In addition, the OLED devices exhibited improved performance in both external quantum efficiency and luminescence efficiency.

Crystalline morphology evolution in PCL thin films

AbstractThe transition of crystalline morphology is revealed in poly(ϵ‐caprolactone) (PCL) thin films as the polymer film thickness changes from hundreds of nanometers to several nanometers. The PCL can crystallize into spherulites, dense‐branching morphology (DBM), or dendrites, depending on the polymer film thickness. It was found that when the polymer film thickness approaches 2Rg (radius of gyration of polymer), there is a remarkable change in crystalline morphology. Under this condition, the polymer crystallization is a diffusion‐controlled process. When the value of polymer film thickness closes to Rg, PCL cannot crystallize, and a dewetting phenomenon will take place. Moreover, polymer morphology can be controlled by varying supercooling. The effect of molecular weight on polymer morphology has been investigated. The main factors that affected pattern formation in nonequilibrium crystallization are also discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1303–1309, 2005