Understanding rate‐limiting processes for the sublimation of small molecule organic semiconductors

Organic small molecules continue to gain attention for application in light‐emitting devices in displays and solid‐state lighting. The purification of these materials by sublimation represents a critical obstacle for their high throughput processing. In this work, we find that the purification of the archetypical hole‐transporting material N,N′‐bis(naphthalen‐1‐yl)‐N,N′‐bis(phenyl)‐benzidine (α‐NPD) is controlled by a combination of viscous flow, Knudsen diffusion, and physical vapor deposition. In contrast with other commercially practiced sublimations, steps like diffusion within the solid feed, desorption from the feed particle surface, and mass transfer within the bed of feed particles, do not significantly affect the sublimation rate. This work provides guidelines for the large‐scale purification of organic semiconductor materials, and possibly for a broader range of high value small molecule specialty materials. © 2014 American Institute of Chemical Engineers AIChE J, 60: 1347–1354, 2014     

A generalized correlation for the prediction of phase behaviour in supercritical systems

A generalized two parameter model is presented which uses molecular properties of pure fluids to predict interaction parameters in the attractive term of the Peng-Robinson equation of state. The predictive method is based on a consideration of London (dispersive) forces and includes attractive forces between polar and non-polar molecules that result from induction. Polar-polar effects and quantum forces are omitted. A large body of experimental vapor-liquid equilibrium data measured at near and supercritical conditions (that excludes quantum components and polar-polar systems) was used to calibrate the generalized model. Overall bubble point pressure deviations calculated using the proposed generalization were 5.66% for 3240 data points which compares to average deviations of 3.27% obtained by using regressed binary interaction parameters. Average vapor mole fraction deviations were just under 0.01 using both the generalized and the regressed interaction parameters. The sensitivity of predicted phase envelopes to dispersive and inductive term in the generalized correlation is shown graphically for several systems. Comparisons are also made to another recent interaction parameter generalization presented by Nishiumi et al. (1988).     

Study on the phase behavior of ethylene–vinyl acetate copolymer and poly(methyl methacrylate) blends by in situ polymerization

This study examines the phase behavior of ethylene–vinyl acetate copolymer (EVA) and poly(methyl methacrylate) (PMMA) blends during MMA polymerization. The ternary PMMA/MMA/EVA mixtures are considered to create a triangular phase diagram, which responds the phase changes during polymerization. The phase changes during MMA polymerization are also examined by optical microscope and photometer. Since the PMMA and EVA are well‐known immiscibles, the polymer solution undergoes phase separation at the initial stage of the MMA polymerization. Additionally, the phase inversion occurs as the conversion of MMA between 13.8 and 20.8%. On the other hand, the EVA‐graft‐PMMA, which can reduce the dispersed EVA particle size, is induced efficiently by taking tert‐butyl peroctoate (t‐BO) as initiator during MMA polymerization. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1001–1008, 2003     

Polyethylene/deutero-polyethylene phase behaviour

A study of the phase behaviour of polyethylene/deuterated polyethylene (PEH/PED) has been carried out to address the question of phase segregation. The phase diagram has been determined by differential scanning calorimetry on carefully co-crystallized mixtures of PEH and PED that are of essentially the same molecular weight. The phase diagram for PEH/PED is compared with one determined for the model alkane system ($\text{C}{}_{36}\text{H}{}_{74}\text{C}{}_{36}\text{D}{}_{74}$) and both are found to be of the type expected for a system forming a series of continuous solid solutions with a narrow liquidus-solidus gap. The relevance of the PEH/PED phase diagram to neutron scattering results, which claim the observation of isotopically driven phase segregation, is discussed.     

Transport models in disordered organic semiconductors and their application to the simulation of thin‐film transistors

Relevant organic thin‐film transistor (OTFT) simulation software must account for the main specificities of organic semiconductors (OSCs) in terms of free carrier density of states, transport mechanisms and injection/collection properties from/to the device contacts. Among the parameters impacting the OTFT performance carrier mobility is a key parameter. Usual methods to extract the mobility from current–voltage measurements lead to only an apparent, or effective, mobility. The value of the apparent mobility is different from the intrinsic channel OSC mobility. Although the effective mobility actually determines most of a given device performance, therefore providing a very useful technology benchmark, it does not describe the intrinsic OSC material transport properties, and may even be misleading in the route to improving the OTFT fabrication process. To obtain a better understanding of the transport properties in OSCs using OTFT electrical characterization, implementing an appropriate physical mobility model in OTFT current–voltage simulation software is mandatory. The present paper gives a review of the carrier mobility models which can be implemented in OTFT simulation software. The review is restricted to analytical and semi‐analytical physical models taking into account the temperature, the carrier concentration and the electric field dependence of the carrier mobility in disordered OSCs. © 2019 Society of Chemical Industry     

Determination of the phase diagram of HBA‐HNA liquid crystalline polymer/polycarbonate blends

The phase diagram of blends of liquid crystalline polymer (LCP) and polycarbonate (PC) was constructed. The effect of temperature on morphological development in melt‐blended samples was examined with a polarized light microscope, in conjunction with a heating stage. Phase separation in the blend was observed as the temperature was increased. For a particular LCP/PC blend composition, two‐phase separation temperatures (T_sp1 and T_sp2) were determined. Consequently, the corresponding phase diagram relating to phase separation was constructed. It was divided into three regions. No phase separation occurred when the blend was below T_sp1. However, a slight phase separation was detected when the temperature was between T_sp1 and T_sp2. Moreover, pronounced phase separation was observed when the blend was at a temperature above T_sp2. The phase‐separated structure varied according to the initial composition of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Poly(butyl acrylate) polymer enhanced phase segregation and morphology of organic semiconductor for solution-processed thin film transistors

The phase segregation as a result of mixing organic semiconductors with polymeric additives has been reported as an intriguing avenue to optimize semiconductor crystal microstructure, active layer composition and charge carrier transport. In this work, we report the mixing of organic semiconductor 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) with poly(butylacrylate) as a polymer additive to control the semiconductor crystal growth and morphology. The incorporation of poly(butylacrylate) induces a vertical phase segregation but a more predominant lateral phase segregation with TIPS pentacene. Along with a solvent vapor annealing technique, poly(butylacrylate) evenly distributes the semiconductor nuclei on the polymer matrix, and results in organic crystal with enlarged grain width. In addition, the randomized crystal growth of TIPS pentacene has been significantly reduced, giving rise to a 25-fold decrease in misorientation angle. The bottom-gate, top-contact thin film transistors with the poly(butylacrylate)/TIPS pentacene mixture as the active layer demonstrated an improved hole mobility of 0.11 cm²/Vs. We believe the phase segregation induced by the poly(butylacrylate) polymer as well as the solvent vapor annealing method as reported in this work can be facilely replicated on other organic semiconductors to realize high performance organic electronic device applications.     

Estimation of phase diagrams for copolymer‐diluent systems in thermally induced phase separation

The binary interaction model was introduced to estimate phase diagrams of copolymer‐diluent systems in thermally induced phase separation. The crystallization curves and cloud points of poly(ethylene‐co‐vinyl alcohol) (EVOH) with 1,4‐butanediol, EVOH/1,3‐propanediol, and EVOH/glycerol were calculated and compared with experimental value or literature data. Fair agreement was obtained. To confirm the importance of incorporating intramolecular interactions, calculations with and without the consideration of intramolecular interactions were performed and compared. It was found that better results can be obtained if intramolecular interaction was introduced. The reason for the small differences between the calculated value and the experimental data of the liquid–liquid phase separation is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

A Fourier transform infra-red study of the phase behaviour of polymer blends. Ethylene-vinyl acetate copolymer blends with poly(vinyl chloride) and chlorinated polyethylene

Fourier transform infra-red studies of ethylene-vinyl acetate (EVA) blends with poly(vinyl chloride) (PVC) and chlorinated polyethylene (CPE) are presented. Previous studies have demonstrated that these blends are compatible at ambient temperature and exhibit lower critical solution temperatures (LCST) in a range that is readily accessible and below the onset of significant polymer degradation. Infra-red spectra of EVA-PVC and EVA-CPE films cast from solution and recorded at room temperature exhibit the familiar frequency shifts and band broadenings of the carbonyl stretching vibration that are consistent with compatible blend systems. Significantly, at temperatures above the LCST, these spectral features are not observed, which implies phase separation. By monitoring the frequency of the EVA carbonyl stretching vibration in samples of the blends, an estimation of the relative strength of the intermolecular interactions has been obtained as a function of temperature. A non-linear relationship is observed and the temperature at which the relative strength of the intermolecular interaction appears very weak correlates with the LCST. The implications of these results are discussed.     

研磨法运用于固相有机合成中的新进展

研磨方法在固相有机合成中的应用研究近二三十年来发展非常迅速,它比传统的有机合成方法更方便和易于操作,在研磨条件下许多传统的反应可以在较温和的条件下进行,或者提高收率、或者缩短反应时间,甚至可以引起某些在传统条件下不能进行的反应。本文主要综述了近年来研磨法应用于固相有机合成中的一些新进展。     

Electrochemistry of metals and semiconductors in fluoride media

The electrochemical surface transformations and diverse applications of a variety of metals and semiconductors in a wide range of fluoride media such as aqueous, non-aqueous media, liquid HF media, room temperature fluoride melts and molten fluoride media with a melting range covering 50–1000°C are reviewed. Nickel shows excellent corrosion resistance in the absence of water. The anodic performance of this metal in electrochemical perfluorination and NF₃ production is discussed. Compact carbon materials serve as anodes in fluorine generators. In high temperature melts, they perform as consumable anodes. Graphitic carbon undergoes intercalation/de-intercalation process and related battery applications. Cu/CuF₂ couple is a good reference electrode. Pt and vitreous carbon materials are the inert electrodes of choice for electro analytical applications. Electrodeposition of Lithium as a non-dendritic uniform phase is important in Lithium metal based secondary batteries. High temperature fluoride melts are used in electro-deposition of valve metals such as Nb, Ta, and Ti. The stability and decomposition of fluoride complexes in these media are of interest.     

Morphology, phase structure and thermal behaviour of films of isotactic polypropylene/hydrogenated oligocyclopentadiene blends: 1. Extruded isotropic films

The effect of hydrogenated oligocyclopentadiene (HOCP) on the structure and morphology of isotropic isotactic polypropylene (iPP) films obtained by melt extrusion has been studied using wide-angle X-ray scattering, thermal analysis and electron microscopy. It was found that the addition of HOCP causes the formation of the smectic phase of iPP at temperatures where bulk iPP crystallizes only in the monoclinic form. The amount of smectic phase present in the blend is dependent on the blend composition. The spherulitic morphology of iPP is completely modified by the presence of HOCP. For blends containing up to 10% HOCP, the iPP spherulite dimensions are drastically reduced. In the case of blends of higher HOCP content, the film crystallinity is reduced, no spherulites are visible and the film surface appears smoother.     

Experimental phase equilibria studies of the PbO–SiO2 system

Phase equilibria of the PbO–SiO₂ system have been established for a wide range of compositions: (i) liquid in equilibrium with silica polymorphs (quartz, tridymite, and cristobalite) between 740°C and 1580°C, at 60‐90 mol% SiO₂; (ii) with lead silicates (PbSiO₃, Pb₂SiO₄, and Pb₁₁Si₃O₁₇) and lead oxide (PbO) between 700°C and 810°C. A high‐temperature equilibration/quenching/electron probe X‐ray microanalysis (EPMA) technique has been used to accurately determine the compositions of the phases in equilibrium in the system. Significantly, no liquid immiscibility has been found in the high‐silica range, and the liquidus in this high‐silica region has been accurately measured. The phase equilibria information in the PbO–SiO₂ system is of practical importance for the improvement of the existing thermodynamic database of lead‐containing slag systems (Pb–Zn–Fe–Cu–Si–Ca–Al–Mg–O).     

Polymer-cosolvent systems: 6. Phase behaviour of polystyrene in binary mixed solvents of acetone with n-alkanes-examples of ‘classic cosolvency’

The demixing behaviour of polystyrene fractions in binary combinations of acetone (1) and a series of n-alkanes (2) containing up to twenty carbon atoms has been established and the data presented as phase contour diagrams. Each binary liquid system exhibits the characteristics of classic cosolvency and the maximum molecular weight of polymer that may be dissolved is ca. 10⁶ gmol^?1 in combinations of acetone and tridecane. The shapes of the phase contour diagrams can be related to the solvent behaviour of the n-alkane used towards polystyrene, although cosolvent action is not a simple linear function of the mixture composition.     

Studies on the transesterification of polycarbonate/poly(ethylene terephthalate) blends. II: Effect of transesterification on the compatibility and crystallization behaviour of the blends

The effect of transesterification on the compatibility of polycarbonate poly(ethylene terephthalate) (PC/PET) blends and the crystallization and melting behaviour of PET was studied. The results show that with increase of the reaction extent, the compatibility of the blends was enhanced during melt-processing, from completely incompatible to partially compatible, then to complete compatibility. In addition, with the increase of reaction extent, the crystallization ability and crystallinity of PET decreased. A new endotherm peak was discerned in DSC thermograms and its position and peak area were closely related to the reaction conditions, which was explained by the changes in the crystalline regions in the PC/PET blends. The effect of transesterification on the multiple melting behaviour of PET in PC/PET blends is also discussed.     

Liquid-liquid phase separation in a polyethylene blend monitored by crystallization kinetics and crystal-decorated phase morphologies

A series of polyethylene (PE) blends consisting of a linear high density polyethylene (HDPE) and a linear low density polyethylene (LLDPE) with an octane-chain branch density of 120/1000 carbon was prepared at different concentrations. The two components of this set of blends possessed isorefractive indices, thus, making it difficult to detect their liquid-liquid phase separation via scattering techniques. Above the experimentally observed melting temperature of HDPE, T_m = 133 °C, this series of blends can be considered to be in the liquid state. The LLDPE crystallization temperature was below 50 °C; therefore, above 80 °C and below the melting temperature of HDPE, a series of crystalline-amorphous PE blends could be created. A specifically designed two-step isothermal experimental procedure was utilized to monitor the liquid-liquid phase separation of this set of blends. The first step was to quench the system from temperatures of known miscibility and isothermally anneal them at a temperature higher than the equilibrium melting temperature of the HDPE for the purpose of allowing the phase morphology to develop from liquid-liquid phase separation. The second step was to quench the system to a temperature at which the HDPE could rapidly crystallize. The time for developing 50% of the total crystallinity (t_1/2) was used to monitor the crystallization kinetics. Because phase separation results in HDPE-rich domains where the crystallization rates are increased, this technique provided an experimental measure to identify the binodal curve of the liquid-liquid phase separation for the system indicated by faster t_1/2. The annealing temperature in the first step that exhibits an onset of the decrease in t_1/2 is the temperature of the binodal point for that blend composition. In addition, the HDPE-rich domains crystallized to form spherulites which decorate the phase-separated morphology. Therefore, the crystal dispersion indicates whether the phase separation followed a nucleation-and-growth process or a spinodal decomposition process. These crystal-decorated morphologies enabled the spinodal curve to be experimentally determined for the first time in this set of blends.     

水盐体系相平衡研究进展

水盐体系相平衡与相图是无机盐化工的理论基础,对水盐体系相平衡的研究可为盐湖盐类资源的综合开发利用提供理论支持。从水盐体系相平衡实验和理论研究两个方面,综述了近期国内外相关研究进展及研究方法。重点介绍了稳定相平衡和介稳相平衡体系相图测定方法及特点,概述了相区间和结晶类型变化的影响因素;从热力学模型法、统计力学理论和分子模拟3 个方面介绍了水盐体系相平衡的理论研究思路及基于液-固化学势平衡的研究现状,并讨论了3 类方法在相平衡研究上的可能发展方向。最后总结了该领域的一些研究热点,并对水盐体系相平衡的研究趋势作了展望。     

Binodal and spinodal curves: a simulation for various high polymer mixtures

Flory's equation-of-state theory has been used to predict the lower critical solution temperature behaviour of polymer—polymer mixtures. The spinodal phase boundary of numbers of high molecular weight polymer mixtures have been previously simulated using this theory. In this paper a procedure for simultaneous predictions of the binodal and the spinodal curves by equating the chemical potential of each component in the mixture is presented. The method is tested for five different mixtures. The effects of the binary and pure component state parameters on the simulated curves are discussed and the simulated phase diagrams are compared with the experimental cloud point curves. It is found that in most cases the results are more consistent with the cloud point curve being closer to the spinodal curve than the binodal.